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PROFESSIONAL

ELECTRICIAN THE BUSINESS MAGAZINE FOR THE ELECTRICAL TRADE

& INSTALLER

THE CPD BOOK

2026: VOLUME ONE

THE CPD BOOK I VOLUME ONE 2026 SECTION 5

SECTION 1 10 The team at NAPIT give our reader submissions the ‘Codebreakers’ treatment

70 The hidden electrical dangers that can occur when they are not checked as part of the standard safe isolation process

12 The experts at NICEIC answer more of your FAQs 14 Considering the impact of BS 9991 on the design of a fire detection and fire alarm system conforming to BS 5839-6 16 A closer look at UK earthing systems, their applications, safety considerations and regulatory requirements to ensure compliant electrical installations 18 How has clamp meter technology evolved over the years? 21 Exploring some of the considerations involved when specifying and installing a DC switch-disconnector

SECTION 2 24 Discussing pollution degree classifications of circuit-breakers, while considering the effects of external influences associated with outdoor installations 27 How to read and interpret graphs that use log-log scales 30 The team at NAPIT give our reader submissions the ‘Codebreakers’ treatment 32 Dr Zzeus, Tom Brookes, answers another fire-related reader question 34 A closer look at the requirements for PEN protection in EV charging applications 37 How contractors must adapt their designs and installations to stay compliant and safe

72 The experts at NICEIC answer more frequently asked questions

14 SECTION 3 41 When is live testing permitted? 44 An introduction to cable calculations 46 The team at NAPIT give our reader submissions the ‘Codebreakers’ treatment 49 The experts at NICEIC answer more frequently asked questions 50 What are the key changes in the recently published updated BS 5839-1: 2025 standard?

74 The team at NAPIT give our reader submissions the ‘Codebreakers’ treatment 76 Examining impedance and its impact on voltage-drop in cables when supplying electrical loads with a poor power factor 79 Discussing the often-overlooked skill of completing an Electrical Installation Condition Report (EICR) accurately and professionally 83 Taking a closer look at the ‘20% rule’, its purpose, application and common misinterpretations

53 How the evolution of smart home technology is transforming domestic electrical installations 56 What are the principles behind MacAdam ellipse and does it mean for lighting?

SECTION 4

90 SECTION 6

58 The essential three-step process for testing the continuity of ring final circuit conductors

86 The team at NAPIT give our reader submissions the ‘Codebreakers’ treatment

60 Understanding SPD internal disconnection and regulatory compliance

88 The experts at NICEIC answer more frequently asked questions

63 The experts at NICEIC answer

89 A look at the process of determining suitable cable sizes for an electrical installation

more frequently asked questions

64 Dr Zzeus, Tom Brookes, answers another fire-related reader question

66 The team at NAPIT give our reader submissions the ‘Codebreakers’ treatment

90 Why do LED lights flicker? 92 Dr Zzeus, Tom Brookes, answers another fire-related reader question

Image References (Adobe Stock): Pg 9 CPD Sign © BeenaTreena Pg 83 20% © Vuang Pg 84 Calculations © Lubos Chlubny

68 Why is the proper connection for neutral conductors so important?

93 How battery storage systems can safely operate in island mode PROFESSIONAL ELECTRICIAN CPD Book 3

@proelectrician

professionalelectrician

Meet the team Editor RICHARD BOWLER email: pe@hamerville.co.uk Digital Manager REBECCA MCGEOCH email: rmcgeoch@hamerville.co.uk Digital Assistant ADAM ROBERTS email: aroberts@hamerville.co.uk Advertisement Manager ANTHONY SCOTT email: ascott@hamerville.co.uk Assistant Advertisement Manager IAN TURNER email: ianturner@hamerville.co.uk Design GEMMA WATSON Production JO WRIGHT Published by: HAMERVILLE MEDIA GROUP Regal House, Regal Way, Watford, Herts, WD24 4YF Tel: 01923 237799 Fax: 01923 246901 Email: pe@hamerville.co.uk

pe@hamerville.co.uk

Professional Electrician, Regal House, Regal Way, Watford, Herts, WD24 4YF

Editor’s Viewpoint

Another busy year of development Welcome to the latest edition of the Professional Electrician & Installer CPD Book – a collection of technical articles and expert guidance designed to support your continuing professional development and help you build valuable CPD hours throughout the year. This publication brings together a range of educational content that has previously appeared in PE’s regular ‘CPD Zone’ sections, providing an accessible reference for electricians and installers committed to keeping their knowledge current. As with all technical information, however, standards and best practice continue to evolve. Since some of the articles featured in this edition were originally published, the introduction of BS 7671:2018+A4:2026 (Amendment 4) means that certain guidance may have been superseded or updated in line with the latest Wiring Regulations.

Amendment 4 introduces significant changes across several areas of electrical installation practice, making it essential that all work is carried out in accordance with the current edition of BS 7671. We therefore encourage all readers to cross-reference the information contained within this book against the latest edition of the Wiring Regulations. If you are unsure how any changes affect your work, always seek advice from your scheme provider, certification body or local technical representative before proceeding. We hope you enjoy the book and that it proves a valuable resource in supporting your ongoing professional development.

Richard B owler

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COMMENT

STAY CURRENT, IN EVERY SENSE Electricians have been voicing concerns over changes to training and qualifications. CEF examines what this could mean for individuals, and for the industry.

n the last ten years, the UK’s electrical skills gap has moved from a distant threat to a day-to-day reality. Demand for electrical work is rising faster than ever, driven by the electrification of housing, promotion of renewable energy and EV, and our increasing reliance on technology. Yet the number of new qualified electricians just isn’t keeping up with that demand. With new qualification criteria and regulatory changes ahead, including the new EAS requirements, that gap is likely to grow even wider. So, what can the industry do to make sure that the required changes to standards and compliance take place without impacting the availability of skills? Is it a case of supporting businesses to take on more apprentices, making training for experienced electricians easier to access, or a combination of the two? At CEF’s recent TechTalks, electricians at different stages of their careers have been voicing their concerns about new training obligations and what they could mean for each of them personally. A growing skills gap Apprenticeship start rates are falling, while a substantial portion of the existing electrical workforce approaches retirement age each year. Put those factors together, and it paints a troubling portrait

6 CPD Book

PROFESSIONAL ELECTRICIAN

of the immediate future of electrical skills availability, at a time when demand is rapidly increasing. That is even before factoring in the additional capacity required by the UK's transition to cleaner energy and transport over the rest of the decade. One of the more surprising aspects of the skills gap is that interest in the profession doesn't appear to be the problem. Large numbers of learners enrol on electrical courses each year, yet only a fraction go on to complete an apprenticeship or start an electrical career. The challenge is helping more of those learners take the next step into the profession, and helping businesses to support them, as well as beneﬁt from them. Part of the challenge is capacity from a business perspective. Taking on apprentices requires time, resource and investment from employers, many of

whom are already stretched trying to keep up with demand. At the same time, those experienced electricians are being asked to keep up with new technologies, evolving regulations and increasing expectations around their own training and qualifications – without managing an apprentice alongside it. Obstacles to existing electricians Addressing the skills gap is as much about keeping experienced electricians in the trade as it is encouraging new ones to enter it. For electricians nearing retirement, new training and qualification requirements can be an obstacle to remaining in the trade, if they’re not handled effectively. With years of hands-on experience in the trade, many question whether it is worth investing both time and money in further qualifications so late in their

careers. In an industry already facing a shortage of skilled people, retaining that experience remains an important and critical part of the wider skills conversation. This is why making training and CPD accessible is so important. Over the past five years, demand for technical training has grown significantly as electricians seek to stay up-to-date with new technologies such as solar PV, battery storage and EV charging, alongside keeping up with changes to standards and regulations. With changes to EAS requirements coming into effect this October, this has become even more pressing and can feel more like an obstacle than an opportunity for time-poor electricians. The challenge for the industry is making that training as accessible as possible, whether that's through local delivery, flexible learning options or practical, hands-on training that fits around the everyday realities of the job. This is an area where businesses are looking for practical solutions. Through its TechTalks, CPD programme and City & Guilds-approved Tech Training courses, CEF has seen first-hand how demand for training has grown in recent years. The focus is not simply on delivering qualifications, but on making them easier to access, through local training locations, online learning where appropriate, and

practical, hands-on courses designed to ﬁt around the day-to-day demands of electrical work. The electrical skills gap won't be solved by a single initiative. The industry needs more apprentices coming through, better routes from education into employment, and support for experienced electricians who continue to develop their skills throughout their careers. If the UK is going to meet the growing demand for electrical work over the next decade, attracting new talent will be important. However, making it easier for people to build and maintain long-term careers in the industry, whatever their current skill level, will be just as essential.

About CEF CEF is the expert supplier of electrical products and services for professional buyers and installers all over the UK. It oﬀers a vast range of products, including leading brands and value alternatives, alongside specialist know-how, friendly advice and support. Established in 1951, privately owned CEF has a UK national network of more than 390 branches and the business now extends to the USA, Canada, Ireland, Spain, and Australia. Customers can place online orders for next working day delivery at cef.co.uk with access to more than 44,000 products from over 300 leading suppliers.

PROFESSIONAL ELECTRICIAN CPD Book 7

Best Best Practice Practice Guides

introduction

WORK THROUGH EACH SECTION AND EARN 6 CPD CREDITs (or 6 hours of learning) TOWARDS YOUR PROFESSIONAL RECORD!

ontinuing professional development (CPD) can be broadly defined as any type of learning you undertake which increases your knowledge, understanding and experiences of a subject area or role. To help professionals to better document and prove this process, the CPD Book contains content and articles that have been checked, verified and accredited by a third-party specialist organisation. Collectively, the content within this specially designed publication has been deemed worthy of 6 CPD credits, or 6 hours’ worth of CPD, with each individual section providing 1 credit, or 1 hours’ worth of CPD. Once this content has been consumed, readers will have the

opportunity to scan a QR code which will provide a bespoke, downloadable certificate that can be used as part of a professional’s ongoing CPD record.

DO NOT SCAN THE QR CODE UNLESS YOU HAVE READ ALL OF THE CONTENT WITHIN EACH SECTION! A large element of CPD involves self-certification and relies on professionals being honest about what they have actually read, consumed and digested. A QR code has been placed with the final article in each of the five learning sections within this publication and ONLY once you have read ALL of the articles within each section, should you then scan the code to receive your bespoke certificate. By skipping any of these steps, you’re not just cheating the system, but yourself and your fellow professionals at the same time!

NEW USERS – ACCESS YOUR BESPOKE CPD CERTIFICATE IN FIVE STEPS 1. Read ALL of the content and articles included within the five sections. 2. Find the QR code with the last article in each section and scan. 3. Enter your email address. 4. Fill out your details on the contact form. 5. Download your certificate for use as part of your annual CPD record. PREVIOUS USERS – ACCESS YOUR CPD CERTIFICATE IN FOUR STEPS 1. Read ALL of the content and articles included within the five sections. 2. Find the QR code with the last article in each section and scan. 3. Enter your name and email address. 4. Download your certificate for use as part of your annual CPD record. All certificates are valid for one year from the issue date. If you’re having any issues with downloading your certificate or using the system, please email us at: pe@hamerville.co.uk

PROFESSIONAL ELECTRICIAN CPD Book 9

THE

CODEBREAKERS ROGER NIGHTINGALE: THIS IMAGE IS OF A REPLACEMENT GAS BOILER IN A SCHOOL. WE WERE ASKED TO LOCATE THE MAINS CONNECTION FOR THE ORIGINAL GAS BOILER. YOU CAN SEE HOW THE PLUMBER AND OURSELVES HAD TO CUT OUT THE WALL TO EXPOSE THE CONNECTION PLATE, WHICH WAS FULLY CEMENTED IN… Part of the periodic inspection and testing process involves carrying out a sample of the terminations within the electrical installation. When terminations exist, such as the connection plate for the boiler – where it has been concealed within the fabric of the building, preventing accessibility for inspection purposes – there may be potential damage to the flexible cable which has been buried within the cement/plaster without any means of protection. The original installation of the connection plate and back box has not been installed to the correct depth to allow the connection to be mounted above the level of the tiles. As a flex connection it would not have been installed with maintenance-free terminations, so would not conform with the requirements of BS 7671. Therefore, the classification code would be a C2, Potentially dangerous, urgent remedial action

required due to the lack of access to the terminations for inspection, maintenance and product replacement.

GET THE BOOK AND CRACK THOSE CODES! Updated for BS 7671:2018+A2:2022, NAPIT’s EICR Codebreakers publication is purpose-written to aid contractors, inspectors and clients, and now includes updates to align with Amendment 2 of the IET 18th Edition Wiring Regulations. The book is the perfect technical aid for electrical professionals and their customers.

10 CPD Book PROFESSIONAL ELECTRICIAN

Need help with cracking those all-important EICR codes? Every month the technical team at NAPIT will be studying your latest ‘Caught on Camera’ photos and oﬀering advice on the next steps, should you find a similar installation. If you want the team at NAPIT to help crack your codes then send your pictures through to us at: pe@hamerville.co.uk

JUSTIN ROBERTS: I WAS CALLED OUT TO A QUOTE FOR A NEW BOARD CHANGE AND FOUND THIS… WESTON POWER HAD TOLD THE CUSTOMER SHE NEEDED A BOARD CHANGE! In certain circumstances, when conducting an EICR, the condition of the installation and associated equipment may be so poor that carrying out a full periodic inspection and testing would serve little practical purpose. Part of the design condition is to consider the external influences that can affect the electrical installation. In this case, we would have to assume that water ingress was not a factor in the original design based on the metal enclosures on the switch-fuses. There has been a change to the installation which has serious degradation from either flooding or water leakage, creating a fire or shock risk to anyone using the installation. The observations on the EICR would cover two areas: a) The service cable, intake and metering equipment are affected by the water ingress, with the equipment floating where the fixings have failed, resulting in strain and stress on the cables and terminations. b) The switch-fuses for the sub mains to the individual flats have suffered serious corrosion to the enclosures, resulting in access to live parts and increased risk of fire or shock. Therefore, the classification code would be a C1, Danger present, risk of injury immediate remedial action required due to the access to live parts and continuing water ingress. With the intake equipment we would normally apply the X and for the person ordering the work to inform the appropriate authority. In this case, however, it would be justified for a C1 to be issued.

The A2:2022 18th Edition Codebreakers publication is priced at £22.00 (members) and £24.00 (non-members). It is available in both hard copy and digital versions * Price is VAT exempt and excludes postage and packaging.

ORDER YOUR COPY OF NAPIT CODEBREAKERS BY VISITING: WWW.RDR.LINK/EBU008

NICEIC. The sign of a serious professional.

Q&A

Q We arewould working in a domestic apartment block What be the maximum disconnection time

Q We have asked toaccount install of some additional k isbeen a factor taking the resistivity,

lighting temperature on existingcoeﬃcient circuits within a school. of and heat capacityAll of the the additional lighting will be installed using conductor material, and the appropriate initial surface-mounted conduit. However, thematerials, existing and ﬁnal temperatures. For common circuits that we are extending are wired the values of k are shown in Table 43.1.using thermoplastic insulated and sheathed cables For a fault of very short duration (less than 0.1 sec), for buriedlimiting in thedevices walls. Do need to upgrade the shall be greater than the current k2S2we circuits to include additional protection? value of let-through energy (I2t) quoted for the Class of

permitted for a device providing protection against cable supports we have installed. overcurrent, e.g.that a short-circuit current? Within the communal area where a suspended ceiling is to be The answer is not a fixed time. A installed, we have supported the cables using steel Regulation 434.5.2 that:Within “A faultthe occurring at any ties to a cable traystates system. individual point in a circuit shallabe interrupted within aceiling time such apartments, where solid plasterboard is that fault current does used not cause the permitted limiting to bethe installed, we have cable anchors and temperature of any conductor orbe cable to ties? be exceeded”. plastic ties. Should these also steel

device to BS EN 60898-1, ENundertaking 60898-2 or A protective The alterations/additions that youBS are

So, there is not a ﬁxed time, it is dependent on the magnitude or size of therequires fault current, thewiring type and A Regulation 521.10.202 that all construction the conductorin and theacross-sectional systems shallofbe supported such way that, in the area of the conductor. HYHQW RI D ΋UH WKH\ ZLOO QRW EH OLDEOH WR SUHPDWXUH

collapse an entanglement risk. The timeand t, in result which aingiven fault current will raise the live conductors thethat highest permissible temperature in Typically, forfrom cables are installed above a normal duty to the limiting temperature can, asofan plasterboard ceiling, it is likely that the means approximation, be calculated from the formula: VXSSRUW ZLOO UHPDLQ H΍HFWLYH IRU ORQJ HQRXJK WR DOORZ SHUVRQV WR HJUHVV WKH EXLOGLQJ DQG IRU ȴUHȴJKWHUV WR k2S2 t= 2 HQWHU WKH EXLOGLQJ DQG GHDO ZLWK WKH ȴUH HWF $OO WKH WLPH I the cables are contained within the ceiling void, and where t is the duration in seconds, the plasterboard is intact, they are protected from the S is the cross-sectional area of conductor in mm2, H΍HFWV RI KHDW DQG ȴUH

is the fault current, amperes, It shouldI also beeﬀective noted that even in theinevent of the expressed for AC as the rms value, due account plasterboards failing, the cables will pass through joists, taken offor the current limiting eﬀect of the where thisbeing is necessary their routing, further limiting circuit impedances, WKH OLNHOLKRRG RI WKHLU FDXVLQJ DQ HQWDQJOHPHQW ULVN )RU WKHVH UHDVRQV WKH XVH RI SODVWLF WLHV RU FOLSV LQ D ȵRRU YRLG DERYH D SODVWHUERDUG FHLOLQJ LV DFFHSWDEOH

BS as quoted by the manufacturer. onEN the61009-1, existingorcircuit(s) would need to meet the 2 requirements BS 7671 70°C (641.5). copper cable with a ﬁnal Example: If a 2.5ofmm temperature rating of 160°C is carryingrequire a fault current of However, this would not necessarily the 200 A, we can use the aforementioned formula to calculate existing circuit to be upgraded, provided that there how long it will be before the cable will reach its limiting ZHUH QR GHIHFWV RU RPLVVLRQV WKDW ZRXOG D΍HFW WKH temperature, after which it will suﬀer thermal damage. VDIHW\ RI \RXU DOWHUDWLRQV RU DGGLWLRQV

From Table 43.1, the k value for a 70°C copper cable with $Q\ GHIHFWV LGHQWLȴHG RQ WKH H[LVWLQJ FLUFXLWV WKDW aZRXOG QRW D΍HFW WKH VDIHW\ RI \RXU SODQQHG ZRUNV ﬁnal temperature rating of 160°C is 115.

The question tells us that the cross-sectional area S = VKRXOG EH UHFRUGHG RQ WKH FHUWLȴFDWLRQ SURGXFHG faultthe current I = 200 A.of regulation 2.5 mm2 and thewith in accordance requirements 2 2 2 2 6HH DOVR WKH DUWLFOH LQ WKLV LVVXH RQ DGGLWLRQV kS 115 ×2.5 13,225×6.25 t DQG DOWHUDWLRQV = 2 = = = 2.07 seconds I 2002VHH /HWȇV JHW WHFKQLFDO S 40,000 Therefore if the overcurrent protective device disconnects the fault current in less than 2.07 seconds, the cable will be adequately protected against thermal damage from the 200 A fault current.

If you are an NICEICFHUWLILHG EXVLQHVV ORRNLQJ for convenient CPD resources, scan the QR FRGH IRU PRUH LQIRUPDWLRQ

SECTION ONE

WHAT’S CHANGED WITH BS 9991? Jake Green, Head of Technical Engagement with Scolmore Group, considers the impact of BS 9991 on the design of a fire detection and fire alarm system conforming to BS 5839-6.

S 9991 has been updated from the 2015 version to the 2024 version.The standard is labelled BS 9991: 2024 Fire safety in the design, management and use of residential buildings – Code of practice. BS 9991 is a ‘code of practice’ and as such provides guidance and recommendations. It is not a specification and should not be treated as such. The scope of the standard is to provide guidance on the design, management and use of dwellings, blocks of flats, residential accommodation blocks having individual bedrooms, specialised housing and care homes, to achieve reasonable standards of fire safety for all persons in and around buildings. BS 9991 is not applicable to HMOs, hotels, caravans, mobile homes, hospitals, places of lawful detention or hostels. Grade and category of system BS 5839-6 provides guidance in Table 1 on the minimum recommended grade and category of system for a range of domestic premises. Furthermore, Approved Document B (England and Wales), Technical Handbook (Scotland), and Technical Booklet (Northern Ireland) also detail minimum recommendations to conform to the relevant Building Regulations legislation. BS 9991 provides further minimum recommendations for grade and category of system for a range of domestic premises types. Flats entered on the same level as the flat – situated more than 4.5 m above ground level

14 CPD Book PROFESSIONAL ELECTRICIAN

The total travel distance from any point of the flat to the entrance door of the flat should not exceed 9 m (clause 8.4.2). However, where the flat is fitted with a Grade D, Category LD1 fire detection and fire alarm system (and contains a sprinkler system) this distance may increase to 20 m. Flats entered from a floor above or below the flat – situated more than 4.5 m above ground level For flats entered from a floor above a Grade D, Category LD1 fire detection and fire alarm system should be provided. Open-plan flat design Open-plan flats should be fitted throughout with a Grade D, Category LD1 fire detection and fire alarm system. Cluster accommodation Cluster accommodation is often found in purpose-built student accommodation. Typically, such arrangements will be a series of bedrooms opening onto a common corridor with a shared kitchen and no additional living spaces. Where this is the case the category of system should be LD1 (BS 5839-6) or L1 (BS 5839-1) for the simultaneous evacuation of residents in the cluster. A smoke detector should be provided in each habitable room and a heat detector in the kitchen. The system should also be linked to the management responsible for the building.

Maisonettes – situated more than 4.5 m above ground level Fire detection and fire alarm system should conform to Category LD1. Active fire protection In line with the recommendations of BS 5839-6, clause 16.1 of BS 9991 recommends that all dwellings are provided with a fire detection and fire alarm system.

“A smoke detector should be provided in each habitable room and a heat detector in the kitchen.” Where automatic fire detection and fire alarm systems are for mixed-use residential buildings, that is having nonresidential as well as residential elements, great care should be taken to ensure that the appropriate standard is applied to each element of the premises (clause 16.2). Annex E – Private balconies and terraces and communal balconies, terraces and roof gardens The normative Annex E details many recommendations and details some specific issues concerning BS 5839-6.

For the means of escape from private balconies and terraces more than 4.5 m above ground level either the interior of the access room should be clearly visible from all parts of the balcony, or as part of the fire detection and fire alarm system a means of detection should be provided in the access room as well as giving warning that is audible on the balcony with the doors closed. The same provision exists where the distance to travel from the balcony access door to the furthest point on the balcony; and there is no alternative escape route. For the means of escape from communal balconies, the automatic fire detection and fire alarm system serving the protected corridors and stairs giving access to the terrace or roof garden should be supplemented by audio and visual alarms. Conclusion Care should be taken by the designer of a fire detection and fire alarm system to not only consider the recommendations of BS 5839-6 (or BS 5839-1 where relevant) but also other relevant standards and codes of practice. BS 9991 provides additional recommendations which should be taken into account by designers of relevant domestic premises. GET MORE DETAILS ON ESP’S RANGE OF FIRE PROTECTION SOLUTIONS BY VISITING: WWW.RDR.LINK/EBU009

PROFESSIONAL ELECTRICIAN CPD Book 15

SECTION ONE

EARTH, WIND AND WIRE Andrew Duﬀen, Technical Commercial Engineer at NAPIT, takes a closer look at UK earthing systems, explaining their applications, safety considerations and regulatory requirements to ensure compliant electrical installations.

n earthing system refers to the method by which an electrical installation is connected to a means of Earth. This connection is primarily for safety reasons, although in some cases, such as telegraph systems, the ground can serve functional purposes – acting as a conductor to reduce the cost of a return wire over extended circuits. In case of a fault in the electrical installation, touching a live metal part can result in an electric shock, as electricity can travel through the body to the ground. Earthing oﬀers an alternative route for fault currents to safely dissipate into the earth. Earthing arrangements For earthing systems, a series of letter coding is used: ● ● ● ● ●

T = terre (Earth) N = neutral C = combined S = separate I = isolated (referring to the connection of the source to Earth)

Five types of earthing systems are deﬁned in BS 7671: ● ● ● ● ●

TN-S TN-C TN-C-S TT IT

TN systems In TN systems, the distribution network operator (DNO) is responsible for earthing, with the two types commonly used within the UK being TN-S and TN-C-S. TN-S system In a TN-S system, there is only one

16 CPD Book PROFESSIONAL ELECTRICIAN

neutral-to-earth connection, located as close as practical to the source (supply transformer). Within a low-voltage supply, a consumer’s earth terminal is connected via the metallic sheath of the distributors supply cable. The metallic sheathing maintains the separation from the insulated neutral conductor within the cable, back to the supply transformer. As this protective conductor is usually metallic (such as steel), the distributor typically declares a suggested maximum external earth fault loop impedance (Ze) of 0.8 Ω. A detailed example of this is displayed in Fig 1 and Fig 2.

TN-C-S systems The TN-C-S system is now quite common in the UK; it allows the distributor to provide a low-voltage supply, due to a reliable earthing arrangement. One form of the TN-C-S earthing arrangement is known as Protective Multiple Earthing (PME), while another is Protective Neutral Bonding (PNB). On the supply side of the system, it relies on the neutral being connected to Earth at the transformer and then combined as one conductor through the supply network – this is known as a Protective Earthed Neutral (PEN) conductor. As part of the system, there are multiple earth electrodes connected to maintain the connection to Earth. At the intake equipment of an installation, this separates into a neutral and earth conductors. Due to the distributor using the PEN as a combined neutral and earth return path, the

suggested maximum Ze being declared as 0.35 Ω. See Fig 3 and Fig 4. TT systems A TT earthing system is typically found in more rural areas in the UK, the neutral reference earthing arrangement is conﬁgured in a similar way as the TN-S, although the distributor does not provide the consumer with an earth connection. The earth connection for the installation is derived from earth electrodes using earth rods or by burying metallic plates/strips/discs into the ground (known as the general mass of earth), which is shown in Fig 5 and Fig 6.

Why use a TT system? A TT earthing system is generally installed where a TN-C-S arrangement is not permitted, for example rural installations where the supply cables are via overhead lines or special locations or installations. Due to the earth return path being provided through the general mass of earth, Ze values may ﬂuctuate where soil types vary, which will require fault protection measures such as Residual Current Devices (RCDs) to provide Automatic Disconnection of Supply (ADS). For a TT arrangement: 21 Ω is the usual stated maximum resistance of the distributor’s earth electrode at the supply transformer ● The resistance of the consumer’s installation earth electrode should be as low as practical ● If the measured Ze exceeds 200 Ω, it may not be stable due to environmental changes, such as drying out in the summer and freezing in the winter

selected for certain parts of electrical installations, when an unexpected disconnection of a circuit could cause danger. This could include medical locations within hospitals, where an IT system is used for circuits supplying medical equipment used for life-support of patients. See Fig 7.

●

Conclusion When designing an electrical installation, one of the ﬁrst considerations is determining the type of earthing system. This information can be obtained from the electricity distributor. For low-voltage supplies provided in accordance with the ESQCR 2002, the typical earthing systems are: ●

IT systems An IT earthing system is uncommon and quite specialist. This is because an IT system is either isolated from earth or is connected to earth through a high impedance (normally above 1,500 Ω). A key characteristic of an IT earthing system is its ability to continue operating without disruption if a fault occurs between lines and Earth, this type of fault is known as a “first fault”. With an IT system, certain specific measures need to be in place. This will include permanent monitoring by a maintenance regime to identify the occurrence of a “first fault”. This must be an audible or visible signal to identify the fault location. IT systems are not permitted for low-voltage public supplies in the UK under the Electricity Safety, Quality and Continuity Regulations (ESQCR). Due to conventional earthing protection being ineffective for this system, this makes it unsuitable for consumer power supplies. An IT earthing arrangement may be

● ●

TN-S TN-C-S (PME) TT

The TN-C system requires an exemption from these under UK regulations, while IT systems are not permitted for low-voltage public supplies. As a result, both TN-C and IT systems are very uncommon in the UK. Understanding and recognising the different types of earthing arrangements used in the UK is a key requirement for all electricians. These various earthing arrangements are crucial for ensuring safety and efficiency in installations. Each earthing arrangement offers distinct advantages tailored to different scenarios, ensuring a robust and adaptable approach to earthing in the UK. This article was designed to help you recognise and understand the different types of earthing arrangements used in the UK. FOR MORE INFORMATION ON NAPIT SCHEME REGISTRATION VISIT: WWW.RDR.LINK/EBU010

PROFESSIONAL ELECTRICIAN CPD Book 17

SECTION ONE

The first transformer clamp invented by Chauvin Arnoux in 1937

The first analogue and digital clamp meters from Chauvin Arnoux

THE EVOLUTION OF CLAMP METERS I In this article the late Julian Grant gives a potted history on the evolution of the clamp meter.

n 1937, Chauvin Arnoux invented the Transformer Clamp, which was the first current clamp to utilise the “split core hinged jaw” system that we see in nearly all clamp meters today. When connected to an appropriate external ammeter, this enabled the AC current flowing in any cable or busbar to be measured quickly and non-intrusively for the first time. Not surprisingly, the transformer clamp and ammeter were soon combined to produce a stand-alone clamp meter, often referred to back then as a ‘tong tester’, with the current directly readable on an analogue display. Novelly, to hold a reading on the display a slider on the back of the clamp meter could be pushed, which literally clamped the display needle in whatever position it was pointing. The operator could then remove the clamp, note the reading, and release the needle.

18 CPD Book PROFESSIONAL ELECTRICIAN

Over the decades clamp meters have evolved to include digital displays, hall eﬀect sensors for DC measurement, and often include a range of typical multimeter functions such as the measurement of voltage and resistance. More recent developments can also calculate and display other more complex functions such as power, power factor, and harmonics. Throughout the decades of evolution, they have all continued to use hinged iron core clamps. That was until Chauvin Arnoux MA400D flexible clamp meter recently...

Introducing the Rogowski Coil Originally invented in 1912 by German physicist Walter Rogowski, a Rogowski coil consists of a helical coil of wire contained in a flexible sheath. There is no iron core. Unlike a traditional current transformer, a voltage is induced in the Rogowski coil, which is proportional to the rate of change of current in the conductor that it surrounds. The voltage output from the Rogowski coil is passed through an integrator circuit, which converts it to provide a current output proportional to that in the conductor. A derivative of the original coil, sometimes referred to as a counter-wound Rogowski, employs a method where the wire from one end returns through the centre of the coil to the other end such that both connections to the coil are made at one end. Being now both open-ended and flexible the Rogowski coil can be looped around a live conductor without disconnecting or disturbing it. Originally somewhat cumbersome devices that could be affected by nearby electrical noise, in more recent years Rogowski coils have reduced in size and increased in performance. Offering much improved immunity to external fields, they are now the current sensor of choice for many test instruments. Compared to a conventional clamp, they are slim, lightweight and bendable, allowing the sensor to loop around conductors in cramped, hard-to-reach spaces or where multiple cables are closely bundled together. In contrast, an iron-core clamp meter requires enough space to fit its rigid jaws around the conductor while ensuring they are closed properly. Any gap or misalignment in the jaws would result in potentially significant reading errors. Flexible clamps can often accommodate much larger conductor

Counter wound Rogowski coil

Rogowski coil with integrator circuit

diameters than conventional clamps and can measure a broader range of current – particularly very high currents – where iron-core clamp meters may saturate or become less accurate. This makes them ideal for measuring currents in large cables or busbars found in industrial and high-power installations. They are also, however, entirely suitable for looping round much smaller cables, such as those found in domestic and light commercial installations, and in this scenario, could be looped around a cable several times to multiply the current reading and improve the Rogowski coils’ bottom-end measurement capability. Rogowski coils typically have a higher frequency response than iron-core clamps, making them suitable for measuring transient currents or highfrequency currents such as those caused by harmonics or switching devices. This is particularly important in modern installations that contain increasing numbers of non-linear loads which produce harmonic currents. Currents with frequencies of up to 5 kHz could be being generated, representing the 100th harmonic in a 50 Hz supply, and this is well within the measurement bandwidth of a Rogowski coil. So many of the conventional clamps in use and available today can only measure currents with frequencies up to 400 or 500 Hz, which will underreport (read low) if higher frequency harmonics are present. The absence of a heavy iron core makes flexible clamps more portable and easier to carry for field engineers or

technicians, and their flexibility further enhances safety in difficult or hazardous environments. Flexible clamps also tend to be more resistant to mechanical damage since they don't have rigid moving parts, like the jaws in a conventional clamp meter. In fact, the only real downsides to a flexible clamp when compared to a rigid iron jaw clamp is that they are not great at very low current measurements, bottoming out at about 100 mA. Multiple wraps around the conductor being measured can reduce this, however. Perhaps more crucially, they also can’t measure DC current. For everything else, perhaps it’s time to ask yourself why you would ever need to use a conventional clamp again. Julian Grant It is with great sadness that PE has to report the death of Julian Grant, after a short battle with illness. Julian, whose career spanned many years at the coalface of the test and measurement sector – most recently with Chauvin Arnoux UK – was well liked and widely known by so many in the industry. He has also generously contributed articles and shared his extensive knowledge with readers of this publication over the last few years. PE extends best wishes and condolences to Julian’s family, friends and colleagues. GET MORE DETAILS ON THE CHAUVIN ARNOUX RANGE OF DIGITAL CLAMP METERS AT: WWW.RDR.LINK/EBU011

PROFESSIONAL ELECTRICIAN CPD Book 19

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SECTION ONE

CONNECTION OF DC ISOLATORS This article from the experts at NICEIC explores some of the considerations involved when specifying and installing a DC switch-disconnector, also known as a DC isolating switch, as a means of isolation between the solar photovoltaic array and the inverter.

here a Solar PV inverter is installed, a means of isolation from both the AC and DC supplies is required (712.537.2.101). This article will focus on DC isolation, which is achieved through a switch-disconnector on the DC side of the inverter (Fig 1).

(b)), making arc extinction more diﬃcult. In AC systems, the natural zero voltage points in the cycle help extinguish electrical arcs during switching. Conversely, in DC systems, the steady-state voltage means that when contacts are separated, the voltage remains, creating a strong

Fig 1. PV component terminology

AC vs DC switching A DC switch-disconnector faces greater challenges than its AC counterpart. With an AC system operating at 50 Hz, the voltage crosses zero twice per cycle, occurring every 10 milliseconds (Fig 2 (a)), which helps suppress electrical arcs. However, DC voltage is constant and lacks this zero-point crossing (Fig 2

Fig 2. (a) AC voltage magnitude as a function of time

electric field within the air gap. This increases the likelihood of air ionisation between the switching contacts, allowing current to bridge the air gap creating an arc. To combat this, DC switches may incorporate a spring-assisted mechanism to enable a fast make-and-break action. Some DC

Fig 2. (b) DC voltage magnitude as a function of time

switches also employ multiple contacts to extend the arc path and aid in arc extinction. What is a switch-disconnector? A switch-disconnector is required for isolation of the inverter, but what exactly is a switch-disconnector? Part 2 of BS 7671 deﬁnes a switch disconnector as: “A switch which, in the open position, satisfies the isolating requirements specified for a disconnector. NOTE: A switch-disconnector is otherwise known as an isolating switch” Switch-disconnectors, or isolating switches, conform to BS EN IEC 60947-3 and are designed for isolation, functional switching, and emergency switching. They are also capable of switching under load. Table 537.4 of BS 7671 provides guidance on selecting devices for these purposes. Switch-disconnectors are categorised for utilisation, the categories for solar PV applications are split into DC PV 0, DC PV 1, and DC PV 2. DC PV 0 is unsuitable for switching on-load and therefore not permissible. DC PV 1 is used for single strings, whereas DC PV 2 is necessary when multiple strings are connected in parallel and there is a risk of overload. DC voltage of a PV string When selecting a DC switch-disconnector, it is crucial to consider the steady-state voltage of the system. A PV system, unlike a

PROFESSIONAL ELECTRICIAN CPD Book 21

SECTION ONE

conventional AC electrical system does not have a set nominal voltage; it depends on the number of PV modules that are connected in series. When specifying a DC isolator, the maximum open circuit voltage (UOC MAX) shall be used (712.512.1.1). This value for a PV string can be determined using Formula 1. Another method for determining UOC MAX is available, although this requires knowledge of the module temperature coeﬃcient and minimum site temperature.

Fig 4. Modules wired in series with a parallel string

Formula 1: UOC MAX = No. of modules × UOC STC × 1.2

Formula 2: ISC MAX = No. of strings × ISC STC × 1.25

Where: UOC MAX is the maximum string open circuit voltage. No. of modules is the total number of modules on the string. UOC STC is the open circuit voltage of the module under standard test conditions as declared by the manufacturer. 1.2 is a multiplier to take account of the voltage rise under a temperature lower than that of standard test conditions.

Where: ISC MAX is the array maximum short-circuit current. No. of strings is the total number of strings in parallel. ISC STC is the short-circuit current of the module under standard test conditions as declared by the manufacturer. 1.25 is a multiplier to take account of the higher irradiance than that of standard test conditions.

DC current of a PV system Knowing the value of DC current that the disconnector will have to interrupt is critical when selecting a switch-disconnector, as higher currents generate more heat in the arc. The magnitude of this current is proportional to the number of PV modules or strings connected in parallel. When selecting equipment for PV arrays, including DC isolators, the short-circuit maximum current (ISC MAX) shall be used (712.512.1.2). Formula 2 can be used to calculate this value.

Determining the maximum current and voltage In order to determine the maximum current and voltage for a DC switch-disconnector, the manufacturer’s details of the PV module are required. An example of this is shown in Fig 5. Using the example data given in Fig 5, determine the maximum voltage and current for selecting a switchdisconnector for a single string containing 20 of the PV modules wired in a series conﬁguration, with no other strings

Fig 3. Modules wired in series configuration

22 CPD Book PROFESSIONAL ELECTRICIAN

connected in parallel. Formulas 3 and 4 can be used to calculate the maximum voltage and current respectively. Formula 3: UOC MAX = No. of modules × UOC STC × 1.2 UOC MAX = 20 × 39 × 1.2 UOC MAX = 936 V Formula 4: ISC MAX = No. of strings in parallel × ISC STC × 1.25 ISC MAX = 1 × 12.5 × 1.25 ISC MAX = 15.6 A Selecting a switch disconnector Once the voltage and current of the system have been determined, the appropriate disconnector can be selected. Firstly, the chosen device must conform to BS EN IEC 60947-3, ensuring it is suitable for on-load switching. The device will bear markings indicating its function; for a switch-disconnector, these markings are illustrated in Fig 6, indicating its capability for making, breaking, and isolating operations. Once the maximum current and voltage have been determined, the appropriate switch-disconnector can be selected. The device’s capability to safely make and break current depends on the system voltage. Due to the differing voltages in PV systems, manufacturers specify a range of voltages along with corresponding safe operating currents for each voltage, tailored to different switching configurations. Table 1 represents hypothetical manufacturer’s data for a DC disconnector.

Table 1. Example DC disconnector current ratings Fig 5. Example of module data

Fig 6. Switch-disconnector symbol from BS EN IEC 60947-3

Using the voltage and current values determined previously, the appropriate wiring configuration can be selected from Table 1. For switching 15.6 A at 936 V, the disconnector should be wired either in a 4-pole series configuration or a 2-pole series + 2-pole parallel configuration. However, it's important to note that this device is not suitable for making and breaking when wired in a 2-pole series configuration. The wiring configurations from Table 1 are illustrated in Fig 7. It should be noted however that these examples are not exhaustive in terms of configurations. Full details should be available in data published by the switchgear manufacturer.

Fig 7. Example wiring configurations of a DC disconnector

It is important that the manufacturer’s instructions for DC disconnector configuration are followed to avoid failure of the device. An example of a burnt-out DC isolator is shown in Fig 8. Other considerations The previous sections described the selection process of a DC isolator, there is clearly more to specifying the correct device compared to its AC counterpart. Consideration should also be given to the termination of the DC conductor in the isolator’s terminals (526.9.1). DC cables generally use class 5 (flexible) conductors. Where equipment terminals are unmarked, they should be suitable for all conductor classes without modification (526.2. Note 2). Some equipment terminals are only suitable for certain classes of conductors without further treatment. Where this is the case the terminals, or if space is insufficient on the product, the immediate unit packaging or technical data sheet should be identified with appropriate markings. Where terminals are only suitable for Class 5 flexible conductors they will be identified with the symbol “f”. Where treatment of the conductors at the terminations is necessary reference should be made to manufacturer’s data, which may state that a fine wire conductor requires a sleeve or ferrule. Where the DC disconnector is located outdoors, it shall be rated for the possible external influences (712.512.102). It is good practice to have the cables entering the bottom of the enclosure through suitably rated stuffing glands.

Fig 8. DC switch-disconnector which failed due to being incorrectly connected.

Summary Selecting a DC switch-disconnector for a Solar PV system presents unique challenges. The maximum voltage and current must be determined before selection of the appropriate device. The conﬁguration at the switch terminals must also be determined to ensure the device can safely make and break the system’s maximum voltage and current. When using ﬁne stranded wire, the terminal of the disconnector shall be suitable, or the cable shall be suitably treated. GET MORE DETAILS ABOUT NICEIC REGISTRATION AT: WWW.RDR.LINK/EBU012

SECTION 1 ENDS! SCAN THE QR CODE TO CLAIM YOUR CPD CREDIT FOR THIS SECTION OR VISIT: WWW.RDR.LINK/EBU013

PROFESSIONAL ELECTRICIAN CPD Book 23

SECTION TWO

POLLUTION DEGREE CATEGORIES Hager’s Technical Training Manager, Paul Chaffers, discusses pollution degree classifications of circuit-breakers, considering the effects of external influences associated with outdoor installations.

ollution degrees help manufacturers and designers select appropriate circuit-breakers and enclosure designs based on the operating environment inside the enclosure. The presence of dust, moisture, or conductive particles can significantly degrade insulation performance, especially in ventilated or outdoor installations. What is pollution degree? Pollution degree (PD) is a classification defined by standards such as IEC 60664 (Insulation coordination for equipment within low-voltage supply systems: Principles, requirements, and tests) and referenced in BS EN IEC 61439 (Low-voltage switchgear and controlgear assemblies) and in circuit-breaker product standards BS EN 60898 and 60947-2. It describes the expected level of environmental contamination that could

Fig 1. Pollution Degree Classifications

24 CPD Book PROFESSIONAL ELECTRICIAN

affect the dielectric strength of insulation within electrical enclosures. This classification is critical for determining clearance and creepage distances, which are essential for ensuring safe operation and preventing insulation failure. See Fig 1 for a better understanding of each category. BS EN IEC 61439 sets out the requirements for low-voltage switchgear and controlgear assemblies and mandates that the pollution degree of the internal environment must match the insulation requirements of the components used. For example, if internal components are rated for PD2 conditions, but the enclosure is installed in an environment where non-conductive pollution may become conductive due to condensation, the risk of dielectric breakdown increases. This scenario requires careful design

consideration, using measures such as: ●

●

Use of filters or sealed compartments to limit ingress of contaminants Heaters or ventilation systems to prevent condensation Upgrading internal components to withstand PD3 conditions (if appropriate to the installation type)

Circuit-breakers to BS EN 60898 BS EN 60898 is the British Standard for low-voltage circuit-breakers for overcurrent protection in household and similar installations. It states that circuit-breakers to BS EN 60898 are intended for use in environments with PD2 conditions but allows for installation in environments with a higher pollution degree, provided enclosures offering the appropriate degree of protection are used. Circuit-breakers to BS EN IEC 60947-2 BS EN IEC 60947-2 is the British Standard for low-voltage circuit-breakers used in industrial, large commercial, and similar installations. It states that, unless otherwise specified by the manufacturer, a circuit-breaker is intended for installation under environmental conditions classified as PD3. Environmental conditions In many applications, ventilation is key

“... installers should not be concerned about using BS EN 60898 circuit-breakers in outdoor enclosures, provided the manufacturer has tested and validated the assembly arrangement as suitable for such use.” to the eﬀective operation of enclosed equipment, especially where heat is generated. It helps maintain performance by keeping internal temperatures within design limits. To reduce enclosure size and cost, natural ventilation using louvres, slots, or vents is commonly used (see Fig 2). When properly positioned, these features can protect against dust and occasional dripping condensate and can be of any length, provided they meet test standards. Ventilation also helps reduce internal condensation caused by temperature and humidity changes. However, it is important to note that ventilated enclosures do not fully isolate the internal environment from the external one. Therefore, pollution degree categories must be considered. BS EN IEC 61439-1 refers to pollution degrees in relation to environmental conditions, including relative humidity and condensation. It highlights that the pollution degree to which devices and components are exposed inside the assembly enclosure (the microenvironment) may differ from that outside the enclosure (the macroenvironment). This difference is due to protection offered by enclosures with specific IP ratings, ventilation, internal heating, or other methods. Outdoor applications For large commercial and industrial outdoor installations, circuit-breakers

Fig 2. Ventilated equipment

conforming to BS EN IEC 60947-2 are recognised as suitable for PD3 conditions (environments where condensation and conductive pollution are expected). This makes them ideal for outdoor use in these settings. However, these devices are intended to be operated only by instructed or skilled persons. In residential applications, there is a limitation: BS EN IEC 60947-2 circuitbreakers are not suitable because they are not designed for operation by ordinary persons. Instead, circuitbreakers to BS EN 60898 must be used in domestic settings. While this standard is based on PD2 conditions (where only non-conductive pollution occurs), it does acknowledge that temporary conductivity, such as that caused by condensation, may occasionally be expected. Therefore, installers should not be concerned about using BS EN 60898 circuit-breakers in outdoor enclosures, provided the manufacturer has tested and validated the assembly arrangement as suitable for such use. In addition to standard switchgear assembly tests such as short-circuit and temperature rise testing, Hager carry out a range of additional tests which exceed the minimum requirements, including condensation and freeze testing. This is to ensure compliance under extreme weather conditions. The enclosure’s intended application, as specified and approved by the original manufacturer, must be clearly documented. For example, a general designation such as 'Outdoor' suggests suitability for typical outdoor environments. However, if there are specific limitations, these must be explicitly stated, for instance, 'Outdoor use without direct exposure to sunlight'.

Conclusion Specifying switchgear and controlgear assemblies for outdoor applications can be a complex task, often accompanied by understandable hesitation due to the need to meet a number of stringent standards. Installers should be aware that when an empty enclosure is purchased and populated independently, the responsibility for compliance with BS EN IEC 61439 shifts to the installer (who is now the assembly manufacturer with the corresponding obligations). This includes ensuring the assembly meets all relevant performance and safety requirements. One effective way to mitigate this risk is by selecting equipment that has been tested and validated for outdoor conditions, including features such as relative humidity and condensation control. Doing so not only simplifies compliance but also enhances reliability and long-term performance in challenging environments. Explore flexible CPD with Hager Academy Looking to deepen your understanding of outdoor enclosures and related design challenges? The Hager Academy is an online learning platform designed for ﬂexible, CPD-accredited courses. Our latest course, “Design Considerations for Outdoor Enclosures,” expands our comprehensive suite of training modules, covering key topics such as renewables, EV charging, and solar PV.

GET MORE DETAILS ABOUT THE COURSE AND HAGER’S FULL TRAINING OFFERING AT: WWW.RDR.LINK/EBV008

PROFESSIONAL ELECTRICIAN CPD Book 25

SECTION TWO

HOW TO USE LOG-LOG GRAPHS In electrical engineering, graphs and charts serve as an essential tool for communication and data representation. The aim of this article from the experts at NICEIC is to look at graphs that speciﬁcally use log-log scales. Such graphs can oﬀer a convenient way to analyse and visualise data in an easy and understandable format once their construction is understood. It is therefore important that electrical contractors are aware of how to read and interpret these graphs.

Note: This article will focus on those found in Appendix 3 of BS 7671 and those issued by manufacturers to assist in the selection of overcurrent protective devices. Logarithmic scale Log-log paper is a resource that makes use of the logarithmic scale where each incremental unit is arranged in a series of uneven bands grouped within repetitive cycles, and which signifies either a tenfold increase or decrease in a quantity. Logarithmic graph paper is a useful way of representing data that covers an extensive range of values1. For instance, it may prove difficult when needing to accurately display data ranging from, say, 0.01 to 1 000 000 on the same scale. However, displaying such information may be achieved using a logarithmic scale that allows each cycle to represent a distinct range, as shown in Fig 1a. Consider the log-log paper in Fig

1a, the horizontal axis starts at 1 within the first cycle which then increases in single lines unevenly spaced to a value of 10. Each subsequent line within the next cycle then represents an increase of 10 up to a 100; then similarly, each further line represents an increase of 100 and so on until 10 000 is reached. Likewise, the vertical axis starts at 0.01 and progresses up to 10 000 in similar steps. However, representation of these values remains undefined until the axes are labelled. The graph shown in Fig 1b shows the characteristic curve of a 32 A fuse to BS 88-2 where the vertical axis shows time (s) and the horizontal axis shows prospective current (A). To demonstrate how to interpret

such a graph, let’s assume a prospective fault current of 250 A has been calculated; the red dotted line intersects the fuse characteristic curve which indicates that the fuse takes approximately 0.4 s to operate. Characteristic graphs in Appendix 3 There are two important observations about the time/current characteristic curves given in Appendix 3 of BS 7671: i. The curves have been cropped at 0.1 s. For disconnections times less than 0.1 s, it becomes necessary to refer to manufacturers’ data. ii. In relation to the curves associated with protective devices to BS EN 60898, the slowest operating times are shown.

1 Logarithmic graph paper can be either log-log, where both scales are logarithmic, or log-lin, where only one scale is logarithmic and the other is linear.

PROFESSIONAL ELECTRICIAN CPD Book 27

SECTION TWO

Fig 1 Log-log graph paper with an example from Appendix 3 of BS 7671

Manufacturers’ charts Where fault conditions result in very short disconnection times of less than 0.1 s, the characteristic curves detailed in Appendix 3 are no longer applicable. The designer will therefore need to consult manufacturer’s data to determine the let-through energy (I2t). Such issues with short disconnection times are generally more of a concern on commercial and industrial installations rather than in a typical domestic installation.

Fig 2 Example of manufacturer’s chart showing the letthrough energy for BS 88-2 fuses. (This chart is for illustration purposes only)

28 CPD Book PROFESSIONAL ELECTRICIAN

The ability of a cable to withstand the energy during a fault and subsequent increase in temperature is dependent on its cross-sectional area (S), resistivity, temperature coeﬃcient, heat capacity of the conductor material, and the appropriate initial and ﬁnal temperature (k). The ‘let-through’ energy generated during the period of the fault is given by the formula: I2t Whereas the thermal ‘withstand’ formula for a cable is given by: k2S2 As such, it is important to remember that the value of k2S2 for the cable is not less than the value of let-through energy (I2t) quoted by the device manufacturer, i.e. I2t < k2S2 (434.5.2). An example chart demonstrating the energy let-through against prospective short-circuit current is shown in Fig 2. Based on the previous example and graph of Fig 1b which considered a 32 A BS 88-2 fuse, what would happen when the fault current is increased to 3 000 A rather than 250 A? From the characteristic curves given in Appendix 3 of BS 7671 it is evident

that the disconnection time will be less than 0.1 s and, therefore, manufacturer’s data will need to be assessed. Using the graph in Fig 2, with a fault current of 3 000 A, the let-through energy (I2t) is about 12 000 A2s. Providing the product of the k factor (Table 43.1 of BS 7671) and the conductor cross-sectional area, both squared (k2S2), is greater than 12 000, compliance with regulation 434.5.2 will be achieved. Summary Log-log graphs are a vital tool used in electrical engineering for analysing and visualising data across an extensive range of values. This article has explained the use of log-log scales, particularly as used in Appendix 3 of BS 7671. Where fault conditions result in a very short disconnection time of less than 0.1 s, manufacturers data charts should always be considered when selecting suitable overcurrent protective devices. GET MORE DETAILS ABOUT NICEIC REGISTRATION AT: WWW.RDR.LINK/EBV007

THE

CODEBREAKERS CHARLIE JONES: THIS WAS A BRAND NEW EV CHARGER INSTALL. THE CONTRACTOR CAME BACK TO RECTIFY IT EVENTUALLY, BUT HOW IS THIS KIND OF WORK BEING SINGED OFF? THE MORE YOU LOOK AT THE IMAGE THE MORE YOU FIND! As a new Electric Vehicle Charge Point (EVCP) installation, it would not normally be considered for periodic inspection and testing. The standard of workmanship observed here is therefore of particular concern. The installation is non-compliant with BS 7671, including the requirements of Section 722, and would require rectification works to make sure the installation is compliant prior to the issuing of the Electrical Installation Certificate. The EVCP cable has not been adequately supported where it terminates within the external intake enclosure. This lack of support would place strain on the terminations and connections. The extended meter tails from the connection blocks to the open connector block have resulted in exposed live parts. This presents a clear danger to anyone accessing the external intake enclosure – DNO, meter operators and the householder reading the meter. The EVCP current transformer (CT’s) conductors also appear to have been terminated within a floating connection unit, which again would place strain on the cables and terminations. Therefore, the classification code would be a C1, Danger present, risk of injury, immediate remedial action required due to the presence of exposed live parts.

30 CPD Book PROFESSIONAL ELECTRICIAN

DAVID SIMPSON: I SAW THIS ON A RECENT JOB – IT’S THE MOST DEGRADED CABLE I'VE EVER SEEN. I THINK IT MIGHT BE A GOOD EXAMPLE OF CABLE (NOT) SUITABLE FOR THE ENVIRONMENT. When designing an electrical installation, selecting the correct cable for the environment is critical for the wiring system to remain safe and serviceable for its expected lifetime of the installation. In this case, the cable that has been utilised for this installation appears to be a flexible cable that has deteriorated significantly. The damage is likely due to eﬀects of ultraviolet radiation, adverse weather conditions or possible vermin damage, resulting in the almost near total breakdown of the outer sheath insulation. At present, there does not appear to be any exposed live conductors, as the internal insulation remains intact, but this would only be a matter of time before it occurs. Although the cable clips do seem to be still supporting the cable in places, they do not mitigate the underlying deterioration. Therefore, the classification code would be a C2, Potentially dangerous, urgent remedial action required due to the damage to the outer sheath of the cable presents an increased risk of insulation failure.

ORDER YOUR COPY OF NAPIT CODEBREAKERS BY VISITING: WWW.RDR.LINK/EBV006

Dr. Zzeus IN THIS REGULAR COLUMN, DR. TOM BROOKES, MD AT ZZEUS TRAINING AND CHAIRMAN OF THE BSI TECHNICAL COMMITTEE FSH 12/1 INSTALLATION AND SERVICING, ANSWERS YOUR QUESTIONS RELATED TO FIRE SAFETY. IN THIS EDITION HE LOOKS TO CLEAR UP SOME RECENT INDUSTRY MISCONCEPTIONS. One of our clients, for whom we conduct fire risk assessments, has been told that across 74 buildings they must now install lift-up clear covers retrospectively on all their manual break-glass call points. They were told it was a major nonconformity because if they have some with cover and some without, it's not the same action. Is this true? It would cost the charity a significant amount of money, rather than being used for people in need. The short answer is no, it is not correct. British Standards are not retrospective; BS 5839-1:2025 is a code of “Best Practice”. Here’s why: I’ve recently been made aware that misinformation circulating on social media claims precisely that if there is no MCP cover, it is a major nonconformity. This is totally incorrect for two reasons: 1) It is not retrospective, which means only new installations need to have lift-up clear covers on them to protect from accidental activation. If a site experiences frequent false alarms with a call point, it is recommended that a cover for false-alarm management be installed. 2) Someone has misinterpreted what “same action” means The action of a manual break-glass call point is either “thumb press” or “hit with a hammer” and has nothing to do with lifting the

32 CPD Book PROFESSIONAL ELECTRICIAN

cover. Clause 44.1.2 lists what we think are Major areas of non-conformity (listed below). If you are taking over maintenance of a fire system, these should all be documented. Major nonconformances that are listed in BS 5839-1:2025 clause 44.1.2: 1. An incorrect number of manual call points to meet the requirements of Clause 19. 2. The method of operation of all the manual call points is not the same – “Thumb press” or “hit with a hammer”. 3. The provision of fire detection is insufficient to conform to the category of system the installation was designed to meet. 4. Heat detection in bedrooms. Again, this is not retrospective. 5. Sound decibel levels that are below the recommendations in Clause 15. 6. Standby battery power supplies that are below the recommendations in 24.3. If there is no standby power supply, it breaches the requirements of the Health & Safety (Safety Signs & Signals) Regulations 1996 7. Non-fire resisting cables are being used rather than fire-resisting cables as required by Clause 25.3. 8. No fault monitoring of the system for power, detection and sounder faults Clause 11.1. This includes auxiliary power supplies and the interfaces through which devices are connected.

9. System integrity that does not meet the recommendations in Clauses 11.2.1, 11.2.9 and 11.2.13. 10. The standards of electrical safety are not in accordance with the recommendations specified in Clause 28. 11. Experience of false alarms, or a history of exposure to them, such that compliance with Section 3 cannot be achieved. 12. Changes to the use, layout, or construction of the protected premises that could affect the effectiveness of the system. 13. Missing zone plan or other correct diagrammatic representation of the building Clause 22.2.5. 14. The fire alarm panel does not have a zonal indication, Clause 22.2. 15. The lack of a facility for the automatic transmission of fire alarm signals from a residential care home to an ARC. DO YOU HAVE A QUESTION YOU'D LIKE ANSWERED? EMAIL YOUR QUERIES TO: TOM@ZZEUS.ORG.UK GET MORE DETAILS ABOUT ZZEUS TRAINING AND THE RANGE OF COURSES ON OFFER AT: WWW.RDR.LINK/EBV009

SECTION TWO

DEMYSTIFYING PEN PROTECTION Viktors Nikolajevs, UK Key Account Manager at CTEK, takes a closer look at the requirements for PEN protection in EV charging applications and dispels a few myths along the way.

s the number of electric vehicle charging points in the UK increases at pace to meet UK government Net Zero targets, so there is an increased safety risk from (thankfully rare) open Protective Earth and Neutral (PEN) faults. Should a PEN fault occur, the entire steel body of the vehicle would become energised and when the user comes in contact with it, they will become the only path to Earth. DNOs report approximately 400 faults per year with typically only 1% resulting in electric shocks. But as the numbers of EVs grow, their increased numbers of users are at risk of electric shock during such PEN faults.

34 CPD Book PROFESSIONAL ELECTRICIAN

When a PEN fault occurs, the user is still at risk of getting an electric shock, even if RCD protection is in place. RCDs will still see the imbalance between the Line and Neutral conductors and break as expected. However, the PE conductor will be eﬀectively live under fault conditions and not break without dedicated means of isolation. The most eﬀective prevention is detecting the fault when it occurs before the end-user comes in contact with an energised vehicle body. Requirements for electrical installations BS 7671:2018+A2:2022+A3:2024 outlines a requirement for PEN fault

protection devices when using PME earthing under clause 722.411.4.1 for chargepoints located outdoors or that might reasonably be expected to be used to charge a vehicle located outdoors. The protection device is supposed to disconnect all live and PE conductors should a fault occur. Alternatively, the clause also permits the use of earth electrodes. However, there is no underpinning BS product standard for PEN protection devices and the clause states that such functionality could be included within the charging equipment. This prompted some EV charging equipment manufacturers to develop a variety of built-in solutions, mostly based

around detection of Phase to Neutral voltage ranges of 207 V to 253 V. Requirements for EV charging equipment standards This approach contradicts the requirements of Section 8.4 of the product standard for all EV charging equipment, BS EN IEC 61851-1:2019 Electric vehicle conductive charging system – General. The section states that for Modes 3 and 4 permanently connected EV supply equipment, protective earthing conductors shall not be switched. EV charging equipment with enabled built-in PEN protection (i.e. the ability to switch PE) do not currently meet the product standard. There is a pending UKonly deviation for this standard that would allow PE switching inside of the charging equipment if the following conditions are met: ●

●

Only manual reset permitted. Automatic reconnection prohibited. Full BSI Kitemark certification via type testing required. Functional test button required.

Not meeting the product standard raises potential issues such as liability in case of injuries and property damage, site insurance policy validity, CE/UKCA marking and certification, and suitability

for grants, such as OZEV, since all of these typically require confirmation of compliance with EN 61851-1. Requirements for OPDD standards IET has recently published IET01:2024 Open combined protective and neutral (PEN) conductor detection devices (OPDDs), which acts as the product standard for devices with PEN protection functionality. The standard describes the operational requirements and their corresponding product markings. Importantly, it increases the operational voltage range to minimise the risks of nuisance tripping in the areas with higher nominal voltage, in some cases from 184 V up to 262.2 V, and in certain cases as far as 273 V. IET01 permits PEN protection to be built-in to the EV charging equipment but drives the point that it must comply with EN 61851-1. This is done in preparation for the deviation mentioned previously and it aligns with requirements such as manual reset only and functional test button requirements for built-in devices. It is important to note, that the extended voltage ranges are likely not to apply to built-in protection devices as EN 61851 will most likely retain the ESQCR voltage references of 207 V to 253V.

Whilst IET01:2024 is not referenced in any other standards or regulations at the time of writing, some of the DNOs have added the compliance with IET01 into the application process. Summary At the time of writing, EV charging equipment with active built-in PEN protection (the ability to switch PE conductor internally) does not meet BS EN IEC 61851-1 requirements in relation to PE conductor integrity within the charging station, pending the deviation. If such devices do not have built-in test buttons and allow for automatic resets, they are also non-compliant with IET01, meaning that some DNOs may reject installation applications. For locations where PEN protection is required, ideally external OPDDs in line with IET01 should be used in combination with EV charging equipment that does not switch PE conductors internally. This will ensure current and future compliance of the EV charging equipment, protective devices and the installation overall. Under Construction (Design and Management) Regulations 2015 (CDM), installers may also be held accountable for using non-compliant equipment, as they may be classed as the system designers. It is the responsibility of system designers to verify the equipment compliance and, if the equipment is found not to be compliant (even if the manufacturer claimed otherwise), the system designers are still completely responsible for the installation design and equipment used. With this in mind, it is always recommended to request the manufacturer’s supply certification from third-party independent bodies such as BSI, Intertek or equivalent, confirming their compliance claims. Please note: information in this article reflects the status of standards at the time of writing and may change. GET MORE DETAILS ON C-TEK’S RANGE OF EV CHARGING SOLUTIONS AND TRAINING SUPPORT AT: WWW.RDR.LINK/EBV010

PROFESSIONAL ELECTRICIAN CPD Book 35

SECTION TWO

FEELING THE HEAT With the rise of renewables, battery storage and electric vehicle charging, the demands on our electrical systems are evolving fast. Jonathan Swain, NAPIT Technical Writer, breaks down how contractors must adapt their designs and installations to stay compliant and safe.

he way we use electricity in our homes and businesses is changing rapidly. The rise of renewable technologies and electric vehicle supply equipment (EVSE) means that load profiles, even within domestic installations, may be significantly higher than ever before, and for much longer durations. Greater care and consideration must now be taken during the design and installation of these systems, and contractors must evolve alongside the technology. For example: your old college electrical lecturer may have taught you, when positioning circuit-breakers in a consumer unit, to place the highest-rated device next to the main switch and cascade down to the lowest. Historically, this would have (mostly) been acceptable, as these circuits were rarely simultaneously and continuously loaded. In today’s world, however, manufacturer’s instructions may now require devices to be suitably spaced to

allow adequate heat dissipation within the consumer unit assembly and to ensure correct operation – particularly when installing systems to supply heat pumps, battery storage, EV charging equipment and solar PV. These circuits will be drawing, or supplying, significant current for sustained periods, meaning breakers are likely to emit more heat in operation (I2R) than a circuit breaker supplying an average upstairs sockets circuit. There is another crucial factor to consider; not only can these circuits present an increase in load – but also an increase in supply. Solar PV and battery storage systems deliver current into the installation, which has implications for how we select and erect systems to ensure they are suitably rated and not at risk of thermal damage.

with other supply sources. Solar PV and battery storage systems operating alongside a primary DNO (Distribution Network Operator) supply fall within this regulation. The new (fifth) indent states:

What does BS 7671 say? An often-overlooked change in Amendment 2 of BS 7671:2018+A2:2022 is an addition to Regulation 551.7.2, which outlines the requirements for installations where generating sets operate in parallel

This regulation requires that the common parts of the installation shall be suitably rated for the combined current that could be simultaneously delivered by each supply source.

PROFESSIONAL ELECTRICIAN CPD Book 37

SECTION TWO

“Greater care and consideration must now be taken during the design and installation of these systems...” In electrical installations without parallel supplies (i.e. from generating sets, fed from a single point of supply), an upfront device typically provides overload protection to a consumer unit and ensures its rating cannot be exceeded. The presence of additional sources, unless correctly configured, could result in more current being delivered to connected loads, with a proportion bypassing the primary protective device and instead coming from the additional source. Failure to account for this in design – resulting in non-compliance with the requirements of Regulation 551.7.2 – could compromise the intended protection of the installation. The potential consequence: thermal damage to an assembly now able to distribute more than its rated current (InA). We will examine three illustrative scenarios showing the impact of the change through Regulation 551.7.2 being put into practice. The intent is to raise awareness of these requirements, especially considering the growing prevalence of multi-source installations. The installations shown are relatively simple to highlight the core concept. In more complex installations, the designer will need to consider the implications across multiple points of an electrical system. Scenario 1 A 100 A (InA) type-tested consumer unit is connected directly to a 100 A service fuse (In), with a final circuit connected to a 3.68 kW inverter with a 16 A design current (Ig). In Fig 1, the rated current of the assembly could potentially be exceeded, making the installation non-compliant.

38 CPD Book PROFESSIONAL ELECTRICIAN

Potential solutions: 1. Install a distribution board rated at 116 A or more (InA). Some manufacturers have tested their 100 A assemblies and can provide a declaration of conformity along with instructions on how to achieve a 116 A conditional rating. 2. If the inverter or gateway has the facility, a Customer Limitation Scheme

(CLS) could be provided. G100-compliant electronic control of the loads and supplies may ensure that the assembly rating is not exceeded. 3. If the installations maximum demand permits, an additional overcurrent protective device could be installed to reduce the In value. This would render the installation compliant; the calculation is now satisfied, as shown in Fig 2.

Scenario 2 In this example, an assessment of maximum demand shows that the full original supply capacity must always be maintained. Installing a switch-fuse isolator, as in Scenario 1, would reduce available current at certain times, i.e. when the PV system isn’t generating. To resolve this, a dedicated renewables consumer unit has been installed, and the switch fuse repositioned, as shown in Fig 3. By installing the switch-fuse isolator, the assembly is sufficiently protected. The current demanded by the consumer unit cannot exceed its InA rating because of the overcurrent protection provided. All parts of the system are suitably rated for the maximum potential current flow they will be subjected to. In this configuration there has been no loss of available capacity as the full 100 A is still available for distribution at the consumer unit. Scenario 3 In previous scenarios, the consumer unit had the capacity to demand greater than its rated current due to the quantity and rating of the circuits connected. As the combined capacity of the supplies could sustain this overload, the installation was non-compliant unless additional overcurrent devices were installed. In Fig 4, however, we can see a similar arrangement – but the connected load has been reduced. In BS 7671:2018+A2:2022+A3:2024, there is precedent that, under certain conditions, a device providing protection

against overload does not necessarily need to be positioned at the start of an installation, as described in Regulation 433.2.2. It even permits the omission of devices for protection against overload where, because of the characteristics of the load or supply, an overload is unlikely or impossible, as described in Regulation 433.3.1[ii]. In this example, overload is not possible by design, protection is provided by the devices in the consumer unit itself. When this method is used to achieve compliance, appropriate labelling is required, as shown in Fig 5. Conclusion Some argue that the perceived risks described here would only arise if there were already a design failure, speciﬁcally, if a part of the installation were overloaded in breach of Regulation 433.1.1. Whilst there may be a degree of truth in this view, it’s important to note that the regulation is a mandatory requirement, and no allowance is made for the application of diversity to meet its requirements. Diversity should never be used as a means of load control and/or overload protection regarding this regulation.

“Some argue that the perceived risks described here would only arise if there were already a design failure...”

Note: Any intended (and documented) departure from BS 7671:2018+A2:2022+A3:2024 requires special consideration by the designer of the installation, and the resulting degree of safety shall not be less than that obtained by compliance with the Regulations. In counter to the criticism: we’ve heard reports of contractors attempting to overcome supply capacity issues by installing microgenerators. Installations evolve, and are added to throughout their service life and, as discussed, many emerging technologies can represent a signiﬁcant increase in current demand. In this light, perhaps even the harshest of critics can appreciate the intent and value of the regulation in the face of a rapidly evolving industry. Traditional, linear supply arrangements are increasingly supplemented by additional sources. Designers must now factor in new dimensions of current ﬂow and protective coordination to ensure safe, compliant installations. FOR MORE INFORMATION ON NAPIT SCHEME REGISTRATION VISIT: WWW.RDR.LINK/EBV011

SECTION 2 ENDS! SCAN THE QR CODE TO CLAIM YOUR CPD CREDIT FOR THIS SECTION OR VISIT: WWW.RDR.LINK/EBV012

PROFESSIONAL ELECTRICIAN CPD Book 39

SECTION THREE

WHEN IS LIVE TESTING PERMITTED? Live testing is permitted, but only where all three conditions of Regulation 14 of the Electricity at Work Regulations 1989 have been met. This article from the experts at NICEIC summarises these conditions as they relate to live testing activities.

egulation 14 of the Electricity at Work Regulations 1989 (EWR) states that: No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless:

(a) it is unreasonable in all the circumstances for it to be dead; and (b) it is reasonable in all the circumstances for him to be at work on or near it while it is live; and (c) suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury. This regulation applies to all activities during which it is necessary to work in close proximity to energised and exposed or inadequately insulated live parts where this may foreseeably give rise to danger. This would include activities such as carrying out the safe isolation procedure, checking the polarity of an incoming supply and testing earth fault loop impedance or RCD functionality. This is conﬁrmed in paragraph 207 of the

Electricity at Work Regulations 1989. Guidance on Regulations (HSR25) published by the Health and Safety Executive (HSE). Let’s consider the three requirements in Regulation 14 that must be met before live work may proceed. 1. It is unreasonable in all the circumstances for the conductor to be dead It is reasonable for testing to take place on or near to a live conductor where the information provided by testing can only be obtained with the conductor energised. For example, the industry-accepted procedure for performing safe isolation requires the supply to the installation or the part thereof to be worked on to be energised initially and to be proven to be energised using a suitable voltage indicator or test lamp. Then, when the installation or that part intended to be worked on is presumed to have been de-energised by

the deliberate operation of a means of isolation, the voltage indicator or test lamp should be used again to prove that the conductors have been made dead by that operation (Fig 1). Similarly, it is reasonable to carry out earth fault loop impedance testing on an energised installation to conﬁrm that the actual, as installed, impedances of circuits are suﬃciently low to allow the disconnection times of BS 7671 to be met under fault conditions.

PROFESSIONAL ELECTRICIAN CPD Book 41

SECTION THREE

However, such testing should only be performed where the protective measures used require a knowledge of earth fault loop impedance (643.7.3.1). In the case of certain sources of supply, such as PV inverters, this information may be obtained from the manufacturer’s data removing the need for such testing which may not provide reliable data in any case due to the nature of the output of the device. It should also be noted that where protection is provided by automatic disconnection of supply (ADS), the effectiveness of this protective measure ‘downstream’ of an RCD may be verified by confirmation of the continuity of protective conductors so removing the need for earth fault loop impedance testing at that point within the installation (643.7.1 a) and b)). Knowing the value of resistance for a circuit’s line and protective conductor (R1 + R2) allows the earth fault loop impedance to be verified using the equation: Zs = Ze + (R1 + R2) A value of earth fault loop impedance for a circuit within the installation may be obtained using the above formula, limiting live testing to measuring of the earth fault loop impedance external to the premises (Ze) only. It should be noted however that, whilst live testing should only be undertaken in line with Regulation 14, a value of Ze obtained by enquiry cannot identify defects external to the consumers installation and as such will not show the actual site condition impedance. Live testing is often carried out to allow the prospective fault current at the origin to be determined. Appendix 14 of BS 7671 advises that: In domestic (household) premises, where a consumer unit to BS EN 61439-3 is used and the maximum prospective fault current declared by the distributor is 16 kA, it is not necessary to measure or calculate prospective fault current at the origin of the supply. 2. It is reasonable in all the circumstances to be at work on or near a conductor while it is live

42 CPD Book PROFESSIONAL ELECTRICIAN

In some cases, equipment may need to remain energised to permit fault finding. However, it does not follow that, having found the fault, there will necessarily be justification for subsequent repair work to be carried out live (HSR25: paragraph 220). Justification for exposing live terminals solely to verify the correct operation of a voltage indicator or test lamp before and after use is arguably more problematic in terms of this condition. Whilst the use of a test lamp or voltage indicator on an energised circuit to prove dead is essential and unavoidable, it is possible to confirm the functionality of such test devices prior to and after such testing by either the integral self-test facility of some voltage indicators (Fig 2), or by the use of a suitable proprietary proving unit (Fig 3). Such methods not only remove the need to expose live parts until it is necessary to confirm that the conductor is energised, but also the need to access another live part after the conductor has been isolated to confirm that the test device is still functioning correctly. 3. Suitable precautions are taken to prevent injury In the context of live testing, suitable precautions to prevent injury include: ●

●

only allowing suitably competent persons who are familiar with the type of installation, the test devices to be used and the work activities to be performed to carry out testing, and the use of suitable testing devices meeting the requirements of relevant product standards and the recommendations given in Electrical test equipment for use on low voltage electrical systems (GS38), and

●

the use of suitable protective equipment as appropriate to the exposure risk (HSR25: paragraphs 221 and 222).

It is essential that all the aforementioned precautions are maintained over time (HSR25: paragraph 223). Testing skills need to be refreshed and instruments, test leads, probes and protective equipment need to be inspected before each use to confirm their continued suitability. Where, for example, routine testing or fault finding is carried out on energised equipment, a suitable precaution might be to cover live parts with a transparent insulating screen in which holes are drilled to enable access to be made to test points. In some cases, it might be appropriate to bring leads out from a test point, to a suitable multi-pin socket-outlet, permitting the use of test equipment in a manner that is not only safer but may also reduce the time required to carry out the necessary testing. Persons carrying out work on or near a live conductor have a legal responsibility for the safety of other persons who may be affected by their actions (EWR: regulation 3). They must therefore take suitable precautions to ensure effective control of the area where live testing is being carried out. A risk assessment should be carried out to determine an appropriate course of action to suit the particular circumstances.

A record of this assessment will be required where an employer has five or more employees. The guidance provided in the Electricity at Work Regulations 1989. Guidance on Regulations (HSR25), Electricity at work, safe working practices (HSG85) and Safety in electrical testing at work

(INDG354) published by the HSE are invaluable to anyone carrying out live testing activities or having responsibility for those carrying out such work. Further information on safe isolation can be found in Best Practice Guide 2 Guidance on the management of electrical safety and safe isolation

procedures for low voltage installations published by Electrical Safety First. Certsure has produced a safe isolation pocket guide within the NICEIC Pocket Guide App that allows electrical engineers and electricians to access this important information while they are working and so keep themselves and others safe. The NICEIC Pocket Guide App is available from the App store for iPhone and iPad and Google Play for Android phones and tablets. GET MORE DETAILS AND DOWNLOAD THE NICEIC POCKET GUIDE APP AT: WWW.RDR.LINK/EBW022 HSR25, GS38, HSG85 AND INDG354 CAN BE DOWNLOADED FREE OF CHARGE FROM: WWW.RDR.LINK/EBW023 DOWNLOAD ESF’S BEST PRACTICE GUIDE 2, AND OTHER BEST PRACTICE GUIDES, AT: WWW.RDR.LINK/EBW024

SECTION THREE

CABLE CALCULATION: AN INTRODUCTION Cable calculation is a simple term for, what in many cases, can be a complex process. Here, Jake Green, Technical Engagement Manager at Scolmore Group, provides an introduction to the subject. The purpose of the cable selection process is to: ●

●

select a suitably sized cable for the environmental conditions which exist, to ensure that all associated protective devices operate under short-circuit, earth fault, and when necessary overload conditions, and to take account of voltage drop ensuring that sufficient voltage exists for the load to correctly function.

This article introduces many of the terms used when determining an appropriate cable size, the applicable requirements found in BS 7671, and a basic process. Unless stated otherwise, all regulation numbers are from BS 7671. Requirements Current-carrying capacities Regulation group 523 details the requirements for current-carrying capacity for conductors. All installed cables must be capable of carrying the rated current without exceeding their rated temperature limit (523.1). Table 52.1 details the maximum operating temperatures for types of cable insulation. These range from 70°C (at the conductor) for thermoplastic

44 CPD Book PROFESSIONAL ELECTRICIAN

insulation to 105°C (at the sheath) for mineral insulated cables. Regulation 523.2 references conformity with Appendix 4 (Table 4A2) as a means of satisfying the requirements of Regulation 523.1.

on the sizing of cables are detailed in Appendix 4 and include: ● ● ● ●

Rating factors All current-carrying conductors will generate heat; this heat must be able to dissipate from the conductor otherwise overheating occurs and the insulation can be damaged. The generated heat is a function of the current and resistance of the conductors; these are often called I2R losses. As current increases the rate of heat loss increases by the square of the current. Cables are designed to operate at the temperature detailed in Table 52.1. Where cables are installed in ways and locations which limit the rate of heat flow from the cable, this must be adjusted for. The rating factors (formerly correction factors) which may impact

● ●

grouping (523.5) ambient temperature (523.8) buried cables thermal insulation (523.9) depth of burial thermal resistivity of the soil.

Cg Ca Cc Ci Cd Cs

An additional factor exists where a semi-enclosed fuse (rewireable) is to be used (Cf) (433.1.202). These factors will be considered in subsequent articles. Voltage drop The voltage at the terminals of any fixed current-using equipment needs to be greater than the lower limit corresponding to the product standard relevant to the equipment (525.1). What this means is that the voltage at the terminals of the connected equipment should be sufficient for the equipment to function as designed. Guidance on the level of voltage

Type of insulation

Temperature limit

Thermoplastic

70 °C at the conductor

Thermosetting

90 °C at the conductor

Mineral (thermoplastic or bare exposed to touch)

70 °C at the sheath

Mineral (bare not exposed to touch and not in contact with combustible material

105 °C at the sheath

Use will be made of It throughout these articles. A simplistic approach to cable calculation may create conditions where conductors are oversized. Reference should be made to Appendix 4, clauses 4 and 5 for a fuller treatment of the varying conditions. drop permitted by BS 7671 is given in Table 4Ab in section 6.4 of Appendix 4 (525.202). For normal supplies the guidance is that lighting should not exceed 3% of the normal nominal voltage, and for other uses a value of 5% is given. These values allow for 6.9 V for lighting circuits and 11.5 V for all other circuits. Overcurrent protection Whilst a cable must be capable of carrying the design current taking into account additional factors impacting on the ability of the cable to dissipate heat, and have sufficient crosssectional area to limit voltage drop, it is important that consideration is given to the nature of the overcurrent protective device(s). Chapter 43 details the requirements of BS 7671 for protection against overcurrent. Regulation 433.1.1 requires that: the rated current (or current setting) of the protective device (In) is not less than the design current (Ib), and

●

the rated current or current setting (In) of the protective device does not exceed the lowest of the current-carrying capacities (Iz) of any of the conductors of the circuit, and the current (I2) causing effective operation of the protective device does not exceed 1.45 times the lowest of the current-carrying capacities (Iz) of any conductors of the circuit.

Simply stated, the design current must not exceed the rating of the protective device, and the protective device must not exceed the current-carrying capacity of the cable. Ib ≤ In ≤ Iz NOTE: Rather than making use of Iz in practical calculations, which requires a process of trial and error, use can be made of It. This value is the tabulated current-carrying capacity and allows for a suitable current-carrying capacity to be readily determined without a process of trial and error.

Introduction to basic cable calculation formulae The calculation order is detailed below: Design current: Single phase: Ib = Three phase: Ib =

P U0 P

√3UL

For more complex circuits consideration will need to be given to power factor and the formulae amended accordingly. Select overcurrent protective device: In ≥ Ib Determine cable size: Where overload conditions may apply: It =

In C

Where overload conditions do not apply: It =

Ib C

(Where C are all the relevant applicable rating factors detailed earlier in this article.) Conclusion In subsequent articles we will consider practical examples for each of the stages and select suitable cable sizes for a variety of conditions. BROWSE THE ELUCIAN RANGE OF CIRCUIT PROTECTION SOLUTIONS IN FULL AT: WWW.RDR.LINK/EBW025

PROFESSIONAL ELECTRICIAN CPD Book 45

THE

CODEBREAKERS JAMES ALLAN: THIS IMAGE SHOWS A DANGEROUS FIND ON A RECENT KITCHEN REFURBISHMENT. ALL THE CONDUCTORS WERE TWISTED TOGETHER WITH NO PROTECTION – I’VE NO IDEA HOW THE WALL WASN’T LIVE. SUSPICIONS WERE FIRST RAISED WHEN I FOUND SURFACE PATTRESSES RECESSED IN THE WALL. THIS WILL ALL BE REMOVED, WITH NEW SUPPLIES AND A NEW CONSUMER UNIT TO BE INSTALLED. Kitchen installations are the most discussed area involving electrical work – from DIYers and handypersons to kitchen fitters and electricians – regarding the low standards of workmanship. Terminations are required to be accessible for inspecting, testing and maintenance purposes, unless they meet any of the bullets from Regulation 526.3 for joints and connections. This includes where they are to be buried in the fabric of the building. The twisting together of the cores of the multiple cables is not an appropriate method of termination and could have led to thermal damage through poor connections. There’s also signs of nail or screw penetration to the plastic oval conduit. Therefore, the classification code would be a C2, Potentially dangerous, urgent remedial action required due to the lack of continuity between circuit protective conductors. If a fault to earth was present through the fabric of the building this situation would be upgraded to a classification C1.

46 CPD Book PROFESSIONAL ELECTRICIAN

GARRY WENT: WHILST CHECKING WHY A BATHROOM FAN WASN’T WORKING ON A RECENT JOB, I FOUND THERE WAS NO EARTH ON THE FAN ITSELF. THIS IS WHAT I DISCOVERED IN THE HALLWAY OUTSIDE THE BATHROOM: A THREE GANG SWITCH WITH THE SUPPLY EARTH CONNECTED DIRECTLY TO THE FACE PLATE OF THE SWITCH AND THE REST OF THE EARTHS WITHIN A WAGO AND NOT LINKED TOGETHER, SO THE FACEPLATE OF THE SWITCH WAS THE ONLY EARTHED ITEM UPSTAIRS ON THE LIGHTING CIRCUIT. IF YOU LOOK CAREFULLY ONE OF THE EARTHS DIDN’T MAKE IT INTO THE WAGO! Defects are often revealed when undertaking fault finding and/or maintenance which, in this case, results in a potentially dangerous situation where the continuity of the earthing system has not been maintained. The original installation was not correctly inspected and tested as the lack of continuity to the fan and other lighting points on the circuit should have been detected and been subject to remedial work for the electrical installation to comply with BS 7671 requirements. The lack of connection between circuit protective conductors to maintain continuity is one aspect, but the poor termination of conductors resulting in conductor cores not being inserted into the terminal block is poor workmanship. All connections are between conductors and equipment shall provide durable electrical continuity. Therefore, the classification code would be a C2, Potentially dangerous, urgent remedial action required due to the lack of continuity between circuit protective conductors. If a fault to earth was present this would be upgraded to a classification C1.

ORDER YOUR COPY OF NAPIT CODEBREAKERS BY VISITING: WWW.RDR.LINK/EBW021

NICEIC. The sign of a serious professional.

Q&A

Q We have been asked to install some additional

A The alterations/additions that you are undertaking

Q We are working in a domestic apartment block What would be the

lighting on existing circuits within a school. All of the additional lighting will be installed using surface-mounted conduit. However, the existing circuits that we are extending are wired using thermoplastic insulated and sheathed cables buried in the walls. Do we need to upgrade the circuits to include additional protection?

expected volt drop cable supports that we have installed. Within the in a 40 metre length communal area where a suspended ceiling is to be of 70°C 2.5/1.5 T&E installed, we have cable carrying 20 supported the cables using steel ties to at a cable tray system. Within the individual Amps an ambient temperature of apartments, where a solid plasterboard ceiling is 30°C? to be installed, we have used cable anchors and plastic ties. answer Should these also be steel ties? The correct

is 14.4 V A Regulation 521.10.202 requires that all wiring Table 4D5 (p456) of systems shall be supported in such a way that, in the BS 7671 (pictured) HYHQW RI D ΋UH WKH\ ZLOO QRW EH OLDEOH WR SUHPDWXUH lists the volt drop for collapse and result in an entanglement risk. 70°C thermoplastic Typically, insulatedfor andcables that are installed above a plasterboard sheathed flat ceiling, cable it is likely that the means of VXSSRUW ZLOO UHPDLQ H΍HFWLYH IRU ORQJ HQRXJK WR DOORZ with protective SHUVRQV WR HJUHVV WKH EXLOGLQJ DQG IRU ȴUHȴJKWHUV WR conductor as 18 mV/A/m. HQWHU WKH EXLOGLQJ DQG GHDO ZLWK WKH ȴUH HWF $OO WKH WLPH Therefore, if the length of the cable run is 40 metres and the contained the ceiling void,volt and the cables currentare being carried within is 20 Amps, the total drop is: the plasterboard is intact, they are protected from the H΍HFWV RI KHDW DQG ȴUH Total Volt Drop (mV) = Volt Drop x Current x Cable Length It should also be noted that even in the event of the Total Volt Dropfailing, (mV) =the 18 xcables 20 x 40 plasterboards will pass through joists, where thisDrop is necessary for their routing, further limiting Total Volt (mV) = 14,400 WKH OLNHOLKRRG RI WKHLU FDXVLQJ DQ HQWDQJOHPHQW ULVN )RU WKHVH UHDVRQV WKH XVH RI SODVWLF WLHV RU FOLSV LQ D ȵRRU YRLG DERYH D SODVWHUERDUG FHLOLQJ LV DFFHSWDEOH

on the existing circuit(s) would need to meet the requirements of BS 7671 (641.5).

However, this would not necessarily require the existing circuit to be upgraded, provided that there ZHUH QR GHIHFWV RU RPLVVLRQV WKDW ZRXOG D΍HFW WKH VDIHW\ RI \RXU DOWHUDWLRQV RU DGGLWLRQV

$Q\ GHIHFWV LGHQWLȴHG RQ WKH H[LVWLQJ FLUFXLWV WKDW Total Volt Drop = 14.4 Volts ZRXOG QRW D΍HFW WKH VDIHW\ RI \RXU SODQQHG ZRUNV VKRXOG EH UHFRUGHG RQ WKH FHUWLȴFDWLRQ SURGXFHG in accordance with the requirements of regulation If this were being fed from a 230 V supply, it would 6HH DOVR WKH DUWLFOH LQ WKLV LVVXH RQ DGGLWLRQV equate to a percentage volt drop of: DQG DOWHUDWLRQV VHH /HWȇV JHW WHFKQLFDO S (Volt Drop)/(Supply Voltage) x 100 = 14.4/(230 ) x 100 = 6.26 %

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SECTION THREE

UPDATES TO BS 5839-1:2025 Jake Green, Head of Technical Engagement with Scolmore Group, looks in detail at a number of key changes in the recently published updated BS 5839-1: 2025 standard.

s with the introduction of all British Standards, other than for BS 7671, the old standard is superseded on the same date as the new one is published. BS 5839-1: 2025 came into eﬀect on 30th April 2025 and the old 2017 version was subsequently withdrawn on that same date. The forward of any standard details some, but not all, of the changes introduced in the new standard. What should also be noted is that BS 5839-1 is a ‘Code of practice’. This means that it provides guidance and recommendations; it is not legislation. This article will highlight several speciﬁc changes and the likely implications for all those involved in the

50 CPD Book PROFESSIONAL ELECTRICIAN

design, installation, commissioning, and maintenance of fire detection and fire alarm systems. Section 1 – General: Introduction All standards contain a foreword detailing the relationship with other standards and specific information about the new document. However, under Section 1 (General) the new Standard differs from the 2017 version by adding an introduction prior to the Scope of the document. This introduction now details the principal purpose of a fire detection and fire alarm system is to ‘support the fire evacuation strategy’ for the building rather than, as the previous standard stated, the ‘fire safety strategy’ for the

building (Clause 6.1 Commentary). This is a subtle but important shift in how the recommendations of this standard should be applied. The focus on the evacuation strategy alone means that the design has a single focus rather than a slightly more general ‘fire safety’ strategy. The introduction also makes much clearer reference to other standards and guidance documents where there are levels of uncertainty. These include: ● ● ●

● ●

BS 9991, BS 9999, Guidance documents that support fire legislation, Insurance documentation, and Any relevant fire risk assessment.

The common practice amongst many contractors seeking to design a fire detection and fire alarm system was/is to ask a manufacturer to design the system and then supply and commission the system to meet the requirements of the design. However, the fire strategy must be considered as of primary importance insofar as the design is concerned. A fire risk assessment is important, but it is not a strategy.

● ●

The amended clause no longer places the responsibility on the designer alone to ensure this consultation takes place. A more collaborative approach is now called for. At the installation stage (Clause 5.3) consultation should happen between: ● ●

Exchange of information and definition of responsibilities The previous Clause 6 (now Clause 5) has an updated commentary as well as amended recommendations. It is important that there is clear communication between relevant parties, and Clause 5 has made things much clearer. Clause 5.1 now recommends that consultations take place prior to the design stage. This has amended the recommendation from the 2017 standard that consultation should take place ‘prior to or at’ the system design stage. These prior consultations should be between: ● ●

● ●

●

User/purchaser, Consultants (to include architects, M&E and fire engineers), Designer, The authority responsible for enforcing fire safety legislation, Property insurer.

At the design stage (Clause 5.2) consultation should happen between: ●

Designer,

User/purchaser, and Consultants.

● ●

Designer, User/purchaser, Consultants, and The supplier of the system.

Again, this amended clause no longer places the responsibility on the installer to ensure this consultation takes place, indeed the installer is not included in the list to this consultation. Where a designer has made a proposal for the category of system (Clause 5.4), this should be agreed with the user/purchaser. This is an important change of emphasis, requiring all relevant parties are able to ‘sign off’ the design. Similarly, the designer should agree with the user/purchaser (Clause 5.5) whether the system incorporates visual alarm devices (VADs). A further change has been made to what should occur prior to the placing of an order for the system (Clause 5.6), and this is to also include ‘handover’ within the list of those with responsibility for each element of design, installation and commissioning. Furthermore, greater clarity has been provided for who is responsible for the creation of the zone plan (Clause 5.7). This should be clearly defined, agreed and documented. Variations (Section 7) Variations have long been an accepted part of the design process. There may be instances, for example, where a thoughtless application of a recommendation would lead to a design which is less than optimal. Indeed, the fire risk assessment process may lend itself to including certain variations. As with the previous standard, any variations must be clearly identified and

recorded in the logbook and relevant certification and should be such that they are immediately obvious to any relevant parties. Previously there were no stated exclusions from permissible variations. This is no longer the case. Clause 6.6 now details those departures which are considered as so detrimental to the safety of the system, that they should be excluded. These excluded items are: ●

●

the absence of a zone plan or other suitable diagrams in which there are more than one zone and particularly where people sleep. The absence of a facility for transmission of an alarm signal to an alarm receiving centre (ARC) in: o Supported housing, or a o Residential home.

This article has only briefly touched on three areas where there have been significant changes to the recommendations of the standard – the introduction, the exchange of information and variations. It is important that all relevant parties make themselves aware of the changes in roles and responsibilities. BROWSE ESP’S RANGE OF FIRE PROTECTION PRODUCTS IN FULL BY VISITING: WWW.RDR.LINK/EBW026

PROFESSIONAL ELECTRICIAN CPD Book 51

SECTION THREE

WIRED FOR CHANGE Steve Humphreys, Technical Commercial Manager at NAPIT, explains how the evolution of smart home technology is transforming domestic electrical installations, highlighting how electricians can futureproof their businesses by gaining the skills and confidence to deliver smart home solutions.

smart home can be defined as “a home equipped with lighting, heating and other electrical appliances that can be controlled remotely”, however, for the electrician and the customer, this definition is too simplistic. A smart home is one where routine manual tasks are automated through technology, enhancing convenience, efficiency and quality of life. Just like the autopilot function in a plane assists the pilot, smart home technologies are designed to assist occupants with minimal manual involvement. Smart home technology has rapidly moved from the realm of science fiction into the mainstream of modern living. Once considered a luxury for the tech-savvy or affluent homeowner, smart home technology is now an accessible, practical and in-demand solution in homes across the UK.

In this article, we’ll look at the evolution of smart home technology, how diﬀerent systems and products work and why electricians are ideally positioned to integrate these technologies into both new and existing domestic installations. For electricians, understanding and installing smart home systems is not just a good business opportunity, it’s fast becoming a professional necessity due to increasing customer demand. Early smart home technology Smart home technology is nothing new. A Scottish company called Pico Electronics developed a domestic smart home system called X10, which was initially installed across North America and later in UK homes in the early 1980s. X10 enabled remote control of appliances and lighting over existing wiring. It worked via small modules (see Fig 1), plugged into sockets or wired into lights, with a central control unit that could send signals to turn devices on or oﬀ. What followed during the 1990s and early 2000s were various wired and wireless systems that used infrared, or

radio frequencies controlled by wall panels. This advanced rapidly with the development of Wi-Fi enabled devices, such as the Hive, launched by British Gas in 2013.

PROFESSIONAL ELECTRICIAN CPD Book 53

SECTION THREE

It’s worth noting that smart technologies have been used in commercial and industrial settings for many decades, to control lighting, security, machinery, robotics, heating, ventilation and air conditioning (HVAC). Many of these applications are now easily integrated into domestic settings. I remember, during my time as an electrician, ﬁtting various commercial, industrial and smart home systems, such as a hard-wired Lutron system that controlled lighting in high-end domestic properties in London. These systems have now moved on leaps and bounds since my time on the tools.

● ● ● ●

Modern smart home technology Early smart home systems like X10 were quite expensive and exclusive, largely due to the high costs of the equipment, such as controllers and other devices. Today, smart home technology has advanced exponentially. It now includes AI-powered voice assistants, IoT (Internet of Things) integrations and mobile applications. Nearly everyone already has a powerful controller, a smartphone. These allow occupants to control smart home systems through software applications as shown in Fig 2. Countless manufacturers now provide high-tech products to make homes smarter and more integrated. This evolution allows smart home technology to reach a much wider market and to be integrated in a lot more areas of the home. Smart home technologies can include:

54 CPD Book PROFESSIONAL ELECTRICIAN

● ●

●

Smart lighting and switches Thermostats and radiator valves Security systems (locks, cameras, alarms) Connected appliances Energy management systems Voice-activated assistants (Alexa, Google Home, Siri) Renewable technology systems (solar PV, EV charging and battery storage)

A major advantage of smart solutions is that they can often oﬀer a better alternative to traditional methods, with beneﬁts such as: ●

● ● ●

Greater cost-eﬃciency for the homeowner Improved time-eﬃciency for the installer Reduced disruption for the homeowner A neat and streamlined solution

Example 1: Lighting Control One example of using a smart home solution could be when adding an additional switch for lighting. The existing switch can be replaced with a smart

retrofit switch and paired with a wireless switch. This setup allows the lighting to be controlled from both the original and new switch locations, via a smart hub, smartphone or even via voice assistant as displayed in Fig 3. Traditionally, adding a second switch would involve installing a cable from the light fitting through floor joists, chasing out the wall, installing a new back box and switch. While straightforward for an electrician, it can be disruptive for the homeowner, involving lifted carpets or floorboards, re-plastering and decorating. Example 2: Heating Control Another example is creating heating zones on an existing combi boiler system with several radiators. Traditionally, this involves draining the system, modifying pipework and wiring electrical control elements. A smart technology solution could involve replacing the boiler’s existing programmer and thermostat with a smart relay unit and a smart thermostat. Existing Thermostatic Radiator Valves (TRVs) can be reused, negating the need to drain the system. Only the TRV heads need be swapped with smart TRVs. The internet gateway is then configured with the thermostat and TRVs via a software application. This setup allows zoning and control of upstairs and downstairs radiators. Typical hardware requirements are shown in Fig 4. As we can see, the potential for system modification and operation through smart home devices is virtually limitless. By utilising the smart solutions outlined in the examples, alterations and additions that typically involve damage and disruption can be avoided.

Who should be installing smart home technologies? Integrating smart home technologies into homes requires varying levels of competence, from a plug and play system, suitable for a DIY enthusiast, to a more complex system needing trained installers or system integrator (see Table 1). There is real opportunity for electricians and other technical trades to enter the smart home technology world. Research shows: ●

●

71% of homeowners would willingly sacriﬁce other home improvements in favour of smart home automation 66% prefer these systems to be professionally installed, despite the growth in DIY options

Mid-range and premium systems require deeper understanding of system design, compatibility and integration. Installation

will involve more complex device conﬁguration, software set up and commissioning. Testing also requires a good level of knowledge as smart devices will not tolerate certain high voltages, such as through insulation resistance testing. A good starting point for electricians is to undertake product training or joining a manufacturer’s partner program. This helps develop an understanding of the various products, systems, platforms and protocols that are out there. Start with simple integrations, like lighting or heating, and build from there.

Conclusion The smart home revolution is no longer on the horizon, it’s here, and it is moving fast. For electricians, this marks a shift in how we design, install and test domestic electrical systems. Understanding and installing smart home technologies is not just a good business opportunity, it’s fast becoming a professional necessity. By embracing this shift, you’ll not only enhance the services you oﬀer, but also position yourself at the forefront of a growing market. Stay informed, get trained and approach each project with both technical insight and customer awareness, and you’ll secure your place in the smart homes of the future. FOR MORE INFORMATION ON NAPIT SCHEME REGISTRATION VISIT: WWW.RDR.LINK/EBW027

SECTION THREE

HOW DOES MACADAM ELLIPSE WORK? Are you getting colour mismatches with your chosen LEDs? In this article the experts at ROBUS tell us more about the principles behind MacAdam ellipse and what it means for lighting.

“

ed wire or blue wire?? Red or blue?!” We’ve all seen the movie moment. Not exactly everyday life for UK electricians (“Brown or blue?!” doesn’t have quite the same ring to it), but there’s no denying it: being able to identify colours correctly is a critical skill. However, for this article, we’re interested in the colour diﬀerence between LEDs rather than wires…

Turns out, we’re all a bit colour blind Is there anything more frustrating than spotting mismatched colours in a design? In the 1940s, physicist David MacAdam – working at Kodak’s research lab – was likely driven by a similar frustration when he began studying how well the human eye can distinguish between diﬀerent colours. We all like to think we have perfect vision that would catch even the slightest

56 CPD Book PROFESSIONAL ELECTRICIAN

difference in shade, but MacAdam proved that there are “invisible zones” – ellipses between colours that the human eye cannot detect. This is where the term MacAdam ellipse (also called MacAdam Step and SDCM) comes from. So, what does that mean for lighting? Key takeaway: MacAdam ellipses are areas on a chromaticity diagram where colour differences are so small that most people can’t tell them apart. Welcome to Standard Deviation Colour Matching (SDCM) Working out whether two LEDs will match is not as straightforward as it sounds. Even in a single batch of LEDs, colour deviations can occur due to manufacturing tolerances. This is measured with the MacAdam ellipses. A five-step MacAdam ellipse usually covers most LEDs in a batch, but some may still fall outside this range. LEDs can

Fig 1. Source: MacAdam, David Lewis (May 1942). "Visual sensitivities to colour differences in daylight" (abstract). JOSA.

also shift in colour as they age, which is why it’s important to choose high-quality, well-matched LEDs from the start. Key takeaway: Most LEDs in a batch fall within a five-step ellipse, indicating standard colour variations allowable while ensuring quality. Colour consistency starts in the manufacturing process The process of manufacturing high-quality LEDs is designed to minimise colour variation from the very beginning. The ﬁrst step in LED production is epitaxial growth, the process of layering semiconductor materials onto a base (substrate) to create the LED chip.

This happens inside a reactor chamber – a tightly controlled environment where precision is critical. Key conditions include:

them by key performance traits like brightness and colour temperature.

Temperature – Must be carefully maintained to ensure even layer formation. Gas flow – Regulated to support accurate semiconductor growth. Substrate quality – A clean, high-quality base is essential for optimal LED performance.

Why it matters Without binning, slight manufacturing variations could lead to visibly mismatched lighting in the final installation.

●

By tightly controlling these variables, manufacturers produce chips that meet strict performance and colour standards, reducing variation before the LEDs even leave the lab. Key takeaway: Achieving colour consistency starts at chip level, but only a trusted manufacturer with tight quality control at every stage can deliver LEDs that perform reliably batch after batch. LED binning: The key to colour consistency After production, LEDs are sorted through a process called binning, which groups Fig 2. Technical and Quality Control teams at ROBUS

Enter MacAdam ellipses These zones on a chromaticity diagram define how much colour variation the human eye can detect. Tighter bins (like 3-step MacAdam ellipses) mean nearidentical LEDs. Cost vs. accuracy Manufacturers must choose bins that balance colour precision with production efficiency. The tighter the bin, the more consistent the light, but also the higher the cost. Not all SDCM is created equal Single-chip ﬁttings, like COB downlights, need tighter SDCM. Why? Because

there’s no hiding place. One LED, one beam, one colour. If it shifts, you’ll see it. But multi-chip fittings (strips, arrays, clusters) are different. The eye blends the light from multiple sources, so minor colour differences average out. A slightly higher SDCM can still look consistent. Selectable or tuneable CCT adds another layer. Manufacturers often quote 1–3 SDCM, and that’s true when each LED channel is powered individually. But once power is spread across two different LED arrays, blending their colours to produce a third colour, tolerances stack up. Thermal shifts, driver variation, optics – it all adds up. This can create a colour deviance which when tested would be representing a higher SDCM, often =<6. Key takeaway: If absolute uniformity is critical (high-end office spaces, premium commercial installs, etc.), stick with fixed CCT and tight binning. ROBUS prioritises high-quality LEDs so customers can trust that what they install today will still match tomorrow, across every batch. BROWSE OR DOWNLOAD THE 2026 ROBUS LIGHTING CATALOGUE AT: WWW.RDR.LINK/EBW028

SECTION 3 ENDS! SCAN THE QR CODE TO CLAIM YOUR CPD CREDIT FOR THIS SECTION OR VISIT: WWW.RDR.LINK/EBW029

PROFESSIONAL ELECTRICIAN CPD Book 57

SECTION FOUR

CLOSING THE LOOP Andrew Duﬀen, Technical Commercial Engineer at NAPIT, explores the essential three-step process for testing the continuity of ring ﬁnal circuit conductors, highlighting the common areas of struggle – from meter preparation to interpreting results.

s most socket-outlet circuits in the UK are traditionally wired as a ring final circuit, electricians and inspectors must have a solid understanding on how to perform the required inspection and testing. They must also be able to understand both the expected and measured readings (results) from the test required. During my time as an electrical tutor, I found this was an area many learners struggled to fully understand. The test is required by Regulation 643.2.1, which is the continuity of ring final circuit conductors. This is a three-step test that ensures continuity of the line, neutral and circuit protective conductors, and confirms correct wiring of a ring final circuit. The measured readings will show if the ring has been interconnected, helping to identify any potential non-continuous ring circuits that may be broken or connected in what is known as a ‘figure of eight’ configuration. A circuit could have breaks but still

appear to be a complete ring. The test also confirms whether any potential spurs (branches from a ring final circuit) are wired correctly. The aim of this article is to refresh your knowledge of how to carry out the test for a ring final circuit, and to improve your understanding of both the expected readings and results obtained. Meter selection and preparation Before performing the test, select a low resistance ohmmeter or multifunction test instrument and confirm that it is in calibration, functions correctly, has suitable battery levels, is free from damage (including test leads and probes) and complies with GS38. Before conducting any continuity tests, it is essential to null the leads. This measures the resistance of the leads and zeros the meter. This is achieved by a closed-circuit lead test ( joining the test leads together). Each meter has its own null or zero function, as shown in Fig 1, or you can note the leads’ resistance and subtract it from your test results.

Circuit preparation If the supply has been energised, carry out safe isolation on the installation, circuit or equipment (see the NAPIT safe isolation procedure). At the consumer unit or distribution board, disconnect the line, neutral and circuit protective conductors (cpc) for the ring final circuit to be tested. This test is performed in three steps: Step 1 Known as the end-to-end resistance test, with the line, neutral and protective conductors being visually identified at the consumer unit/distribution board, and the resistance of each is measured separately, as displayed in Fig 2. a) line to line = r1 b) neutral to neutral = rn c) cpc to cpc = r2 Acceptable readings will confirm there is no open circuit fault on each conductor.

58 CPD Book PROFESSIONAL ELECTRICIAN

Step 3 Again, calculate the expected value using the results from Step 1.

Measurements should be similar (industry best practice is within 0.05 Ω) if all conductors are of the same cross-sectional area (csa). If the cpc has a reduced csa, the r2

I would have my learners record the result in the “Remarks” column of the Schedule of Test Results, as this is useful information for the next inspector.

value will be proportionally higher than the line and neutral values. For example, if the line and neutral conductors were 2.5 mm2 and the cpc is 1.5 mm2, the r2 resistance should be 1.67 x r1 or rn. This is because the line conductor’s csa is 67% larger than the cpc (2.5 ÷ 1.5 = 1.66666667). Unexpected readings may indicate: ●

●

Lower than expected – possible ‘ﬁgure-of-eight’ connection, conﬁrmed in Step 2 Higher than expected – possible loose or faulty terminations No reading – possible break in the conductor ring

Step 2 This step is often forgotten or, at times, not carried out as there is no designated place to record the gained result on the test certiﬁcate. As I cast my memory back to my time teaching, I would always stress the importance of conﬁrming continuity and polarity checks.

At the consumer unit/distribution board, cross-connect the outgoing line conductor to the returning neutral conductor and vice versa. Measure the resistance at each point on the circuit. Readings should be close to the calculated value at Step 2 as shown in Fig 3. Any points wired as spurs will show a higher resistance value. If using pvc single-core cables, ensure that line and neutral conductors of the opposite ends from the ring ﬁnal circuit are identiﬁed and connected together correctly, as they may not be marked; this was often the case from my experiences during my time served as an inspector and tester.

The open ends of the line and cpc conductors at the consumer unit/distribution board are cross-connected, i.e. the outgoing line conductor is connected to the returning cpc conductor and vice versa. Measure the resistance between the line and cpc at each point. Readings should be close to the calculated value at Step 3, with spurs showing higher resistance. The highest value will represent the maximum R1 + R2 for the circuit, and should be recorded in the correct column of the Schedule of Test Results. Conclusion Electricians and inspectors must not only carry out continuity tests on ring final circuits correctly, but also fully understand the meaning of the results that are recorded. This is not simply a box ticking exercise, it directly underpins the safety, functionally and compliance of the circuit. From teaching this method to learners and supporting electricians in the field, I know first-hand how easily the subtle details can be missed. Interpreting values gained are at times overlooked or misunderstood, yet these are the very clues that flag hidden issues before they become dangerous faults. The three-step test method described here verifies the process and deepens your ability to interpret readings. A thorough understanding of your results is more than good practice, it’s what keeps installations safe. FOR MORE INFORMATION ON NAPIT SCHEME REGISTRATION VISIT: WWW.RDR.LINK/EBX013

PROFESSIONAL ELECTRICIAN CPD Book 59

SECTION FOUR

INTERNAL DISCONNECTION OF SURGE PROTECTIVE DEVICES Umer Farooq, Technical Product Manager at Live Electrical, provides more understanding of Surge Protective Device (SPD) internal disconnection and regulatory compliance.

urge protective devices (SPDs) have become a routine feature in both domestic and industrial installations following the 18th Edition of the Wiring Regulations, which expanded the circumstances under which protection against transient over-voltages is required. This article outlines the regulatory framework governing SPD overcurrent protection and explains how modern internal disconnection technology operates, particularly in busbar-connected or directly isolator-connected configurations commonly used in installations with a conditional short-circuit current rating of 16 kA. Regulatory framework and the role of the SPD disconnector The Wiring Regulations define an SPD disconnector as a device intended to disconnect an SPD, or part of an SPD,

from the power system. Its purpose is to prevent persistent fault conditions and to provide indication of SPD failure. Disconnectors may be internal (integrated within the SPD) or external, and more than one disconnection function may be present, for example, thermal protection or overcurrent protection (Part 2 – Definition Regs). With respect to overcurrent protection, the Regulations require that: ●

●

SPD installations shall be protected against overcurrent with respect to short-circuit currents. Such protection may be internal and/or external, in accordance with the manufacturer’s instructions (Regulation 534.4.5.1).

The requirement is performance-based. It does not mandate the automatic inclusion of a dedicated OCPD in every case; rather, it requires that the SPD be adequately protected against the prospective short-circuit current at its point of connection, either directly or through coordinated protection. Hybrid technology and internal protection Modern hybrid SPDs are designed to manage two fundamentally different stress conditions: ●

●

Transient surge events (lightning impulses or switching surges). Abnormal sustained conditions, such as temporary overvoltage or internal degradation.

A typical single-phase & three phase hybrid SPD comprises:

60 CPD Book PROFESSIONAL ELECTRICIAN

Fig 1. Internal wiring of SPD

1. Metal oxide varistor (MOV) between Line and Neutral for voltage limitation. 2. Gas discharge tube (GDT) between Neutral and Earth for controlled energy diversion. 3. An integrated thermal disconnector mechanically linked to the MOV. 4. A visual status indicator activated by a spring mechanism upon disconnection. The MOV responds rapidly to transient overvoltages, while the GDT provides controlled high-energy discharge to earth. The integrated thermal disconnector is mechanically coupled to the MOV and operates when excessive temperature rise occurs. This temperature rise may result from sustained overvoltage, internal degradation, temporary overvoltage (TOV), or abnormal short-circuit stress demonstrated during type testing. When the defined thermal threshold is reached, the mechanism separates the affected protection path, ensuring the SPD transitions safely to an open-circuit condition.

coordinated with upstream protection, the SPD has been assessed to transition safely to an isolated condition.

Short-circuit behaviour and disconnection criterion Under BS EN 61643-11, SPDs are subjected to defined short-circuit and conditioning tests. In the 100 A test set-up, compliance may be demonstrated if the SPD: It is important to distinguish between: ●

●

Either disconnects within five seconds during the application of the conditioning voltage, or Limits the post-conditioning current to define safe values.

This confirms that the internal disconnector can operate in a controlled manner under abnormal electrical stress. In addition, the SPD in question carries a declared short-circuit current rating (Isccr) of 300 A. This rating represents the maximum prospective short-circuit current at the SPD connection point for which safe behaviour has been verified during type testing.

Key design considerations When assessing whether an additional overcurrent protective device (OCPD) is required, designers should verify:

Thermal disconnection due to sustained overvoltage or end-of-life degradation, and Protective isolation under abnormal short-circuit stress within the declared rating.

●

The internal disconnector is not limited solely to end-of-life scenarios; its operation forms part of the device’s verified protective behaviour under defined abnormal current conditions during testing. Where the prospective short-circuit current does not exceed the declared Isccr and the installation is

●

The SPD’s declared short-circuit current rating (Isccr). The prospective short-circuit current at the point of installation. The maximum upstream protective device rating permitted by the manufacturer. The consumer unit’s conditional short-circuit capability. GET MORE DETAILS ABOUT LIVE ELECTRICAL’S RANGE OF CIRCUIT PROTECTION SOLUTIONS BY VISITING: WWW.RDR.LINK/EBX014

NICEIC. The sign of a serious professional.

Q&A

NICEIC FAQs Each month, our of technical expert, technical engineers essential questions NICEIC’s team of team expert, engineers answeranswer essential questions from IURP 1Ζ&(Ζ& FHUWLȴHG EXVLQHVVHV Ȃ KHUH DUH WZR RI WKH ODWHVW TXHULHV NICEIC-certified businesses – here are a few of the latest queries. If the metal armour of a cable is being used as have been questioned over the types of a Q and protective conductor, does it require green and yellow cable supports that we have installed. Within the colour identification? communal area where a suspended ceiling is to be installed, we have supported the cables using steel No. A ties to a cable tray system. Within the individual Regulation 514.6.1 states that “Identification by colour or apartments, where a solid plasterboard ceiling is marking is not required for: to be installed, we have used cable anchors and (i) concentric conductors of cables plastic ties. Should these also be steel ties? (ii) metal sheath or armour of cables when used as a protective conductorrequires that all wiring A Regulation 521.10.202 systems shall be supported in such a identification way that, in the (iii) bare conductors where permanent is not HYHQW RI D ΋UH WKH\ ZLOO QRW EH OLDEOH WR SUHPDWXUH practicable collapse and result in an entanglement risk. (iv) extraneous-conductive-parts used as a protective Typically, for cables that are installed above a conductor plasterboard ceiling, it is likely that the means of (v) exposed-conductive-parts used as a protective VXSSRUW ZLOO UHPDLQ H΍HFWLYH IRU ORQJ HQRXJK WR DOORZ conductor”. SHUVRQV WR HJUHVV WKH EXLOGLQJ DQG IRU ȴUHȴJKWHUV WR HQWHU WKH EXLOGLQJ DQG GHDO ZLWK WKH ȴUH HWF $OO WKH WLPH the cables are contained within the ceiling void, and the plasterboard is intact, they are protected from the H΍HFWV RI KHDW DQG ȴUH

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it possible a new circuits installation to include a on for existing within a school. All of Q Islighting

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non-compliance BS 7671 still have an Electrical the additional with lighting willand be installed using Installation Certificate? surface-mounted conduit. However, the existing circuits that we are extending are wired using Yes thermoplastic insulated and intended sheathed cables Regulation 120.3 states that: “Any departure buried in the walls. Do we need to upgrade from these Parts requires special consideration by the the circuits of tothe include additional protection? designer installation and shall be recorded on

electrical certification specified in Part A the Theappropriate alterations/additions that you are undertaking 6.onThe of safety the installation theresulting existingdegree circuit(s) wouldof need to meet the shall be not less than that obtained by requirements of BS 7671 (641.5). compliance with the Regulations”. However, this would not necessarily require the So, it is possible to have a non-compliance existing circuit to befrom upgraded, provided (intended departure) BS 7671, but the that there ZHUH QR GHIHFWV RU RPLVVLRQV WKDW ZRXOG D΍HFW WKH non-compliance must be recorded on the VDIHW\ RI \RXU DOWHUDWLRQV RU DGGLWLRQV certificate for the new work and the installation’s

safety must not be less that if BS 7671 had been $Q\ GHIHFWV LGHQWLȴHG RQ WKH H[LVWLQJ FLUFXLWV WKDW fully complied with. ZRXOG QRW D΍HFW WKH VDIHW\ RI \RXU SODQQHG ZRUNV The NICEIC Electrical Installation Certificate VKRXOG EH UHFRUGHG RQ WKH FHUWLȴFDWLRQ SURGXFHG includes a section forthe detailing any departures from in accordance with requirements of regulation BS 7671, as shown below, left. 6HH DOVR WKH DUWLFOH LQ WKLV LVVXH RQ DGGLWLRQV We would also VHH /HWȇV JHW WHFKQLFDO S recommend attaching the DQG DOWHUDWLRQV associated evidence to confirm that the departure is no less safe than having complied with BS 7671.

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Dr.Zzeus IN THIS REGULAR COLUMN, DR. TOM BROOKES, MD AT ZZEUS TRAINING AND CHAIRMAN OF THE BSI TECHNICAL COMMITTEE FSH 12/1 INSTALLATION AND SERVICING, ANSWERS YOUR QUESTIONS RELATED TO FIRE SAFETY. IN THIS EDITION HE OFFERS GUIDANCE ON ALTERNATIVES TO FIRE ALARM SOUNDERS. Q. I’ve been asked by the owners of a zoo’s animal hospital whether we can remove the fire alarm sounders from the treatment areas, as they’re causing distress to the sick animals. I thought of installing beacons instead?

If sounders are removed to reduce animal distress, the visual devices become the primary life safety warning system. When any device becomes the primary method of alarm: ● ● ●

Yes, in some circumstances sounders may be removed or reduced in treatment areas where loud audible alarms would cause distress to animals or interfere with clinical care. However, you must still provide an effective alternative means of warning occupants of a fire. The fire alarm system must still reliably alert staff so that appropriate action can be taken. A suitable alternative is the use of Visual Alarm Devices (VADs). These provide a clear visual warning of a fire alarm condition and are specifically designed, tested and certified to perform that life-safety function. Standard flashing beacons or Visual Indicating Devices (VIDs) must not be used as the primary method of fire alarm warning. VIDs are intended only as supplementary indicators and aren’t designed or certified to provide life-safety alarm warning. If visual warnings are relied upon as the main method of alerting occupants, the devices must be BS EN 54-23 certified Visual Alarm Devices (VADs). These are specifically designed to provide a defined level of illumination to warn occupants and enable evacuation or response.

64 CPD Book PROFESSIONAL ELECTRICIAN

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Its performance must be defined Its coverage must be proven Its reliability must be certified It must meet recognised fire alarm standards

BS EN 54-23 certiﬁed Visual Alarm Devices meet these requirements. You must ensure you have the correct type for the location you’re installing: ●

● ●

Category ‘C’ for ceiling-mounted devices Category ‘W’ for wall-mounted devices Category ‘O’ (open) where performance is deﬁned by the manufacturer

Another option that could be considered is a vibrating pager system linked to the fire alarm, where each member of staff carries a pager that vibrates when the alarm activates. This can provide an additional means of alerting staff, particularly when attention is focused on treatment procedures. However, such systems are usually more expensive to install and typically involve ongoing annual service or monitoring charges, and they’re normally regarded as a supplementary alerting method rather than a replacement for compliant alarm devices.

Before any changes are made, the building’s fire risk assessment should be reviewed, and it would be prudent to consult the zoo’s fire risk assessor. They may require additional management measures to support the revised warning strategy, such as a buddy or sweep system where staff in areas that still have sounders confirm that treatment area staff have seen the visual alarms. They may also require updated procedures and staff training so that everyone understands how the new alert method works in those areas. In summary, sounders can be removed from animal treatment areas, where justified, but the fire alarm system must still provide an effective warning. If visual alarms are relied upon as the primary means of alert, BS EN 54-23 certified Visual Alarm Devices must be used. Standard beacons or VIDs cannot be relied upon for this purpose. Any change should be supported by the fire risk assessment and appropriate operational procedures to ensure the safety of staff and occupants is maintained. DO YOU HAVE A QUESTION YOU'D LIKE ANSWERED? EMAIL YOUR QUERIES TO: TOM@ZZEUS.ORG.UK

THE

CODEBREAKERS JIM TOYNE: AS AN ELECTRICIAN, I WENT TO DO A JOB AT MY DAUGHTER’S NEW BUILD HOUSE. ZOOM IN AND LOOK AT THE UPSTAIRS LIGHTING MCB 32 A. THE DATE ON THE CONSUMER UNIT STATES THAT IT WAS TESTED APRIL IN 2025! Whenever there is a request to replace an item of electrical equipment such as a distribution board we do need further information regarding the existing installation. If we were looking at a like-for-like replacement there wouldn’t be many areas for discussion or review. But when we come across a situation as shown in the photographs, there are many inherent non-conformities which would have to be investigated and subject to remedial works before such a replacement could be carried out. At first glance the distribution board looks fairly new but once the cover is opened, we can see missing blanks with exposed live parts where the copper bars are accessible. With the cover removed further issues are revealed: there are ‘floating contactors’ which have not been provided with a means of fixing and it isn’t clear if the control circuits are supplied from the same distribution board. The openings at the top of the distribution board do not meet the requirements of IP4X where the metal trunking hasn’t been extended to the end of the distribution board, allowing access to

live parts and single insulated conductors. The metal trunking has similar issues where the containment doesn’t meet the IP4x. Therefore, the classification code would be a C1, Danger present – immediate remedial action required, for exposed live terminals of accessible at the distribution board.

66 CPD Book PROFESSIONAL ELECTRICIAN

PAUL SHACKLETON: I’VE NEVER SEEN THIS BEFORE. THERE WAS AN UNDERGROUND CABLE FAULT AND THE SUPPLY AUTHORITY INSTALLED A TEMPORARY GENERATOR TO THE HOUSE WHILST DIGGING THE ROAD. THEN, WHEN THEY RE-INSTATED THE MAINS SUPPLY THEY SWAPPED THE LINE AND NEUTRAL – LUCKILY THE CUSTOMER NOTICED! (THE PICTURE WAS TAKEN WHEN THE ENGINEER ARRIVED TO CORRECT IT). IT JUST GOES TO SHOW THAT YOU NEED TO CHECK EVERYTHING, EVEN WHEN IT SEEMS IMPOSSIBLE THAT ANYTHING COULD POSSIBLY BE WRONG. Often, when maintenance is carried out on an existing installation, it may not be immediately evident that the work has fundamentally changed the safety of the installation. For this reason, those working on electrical installations must be suitably skilled and competent. As part of the periodic inspection and testing process, the polarity of the incoming supply must be verified, although a visual inspection may confirm the correct termination within the installation, meter tails from the service cut-out via the meter require polarity checks. The incorrect termination of the meter tails at the service cut-out fuse would lead to a potentially dangerous situation within the property where the single-pole devices would be switching the ‘Neutral’ of the circuits. In this case, it was fortunate that the issue was identified by the customer at the time, or it could otherwise have gone undetected until the next periodic inspection. Therefore, the classification code would be a C2, Potentially dangerous, urgent remedial action required due to the lack of protection for the installed conductors and potential thermal damage to the OCPDs.

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SECTION FOUR

THE IMPORTANCE OF PROPER CONNECTION FOR NEUTRAL CONDUCTORS Poor connections, particularly those involving neutral conductors, are often identified during electrical inspection and testing, with some incidents periodically reported to the NICEIC. If these issues remain unrectified, they can lead to thermal distress, conductor/connection failure or possibly cause fires. In this article NICEIC’s experts explain why it is therefore essential to apply the same level of diligence when connecting or inspecting neutral conductors as with any other live conductor.

t should be remembered that a neutral conductor is a live conductor. Part 2 of BS 7671 defines a live part as:

Regulation 524.2.1 also requires that the neutral conductor, if any, shall have a csa not less than that of the line conductor:

‘Live part. A conductor or conductive part intended to be energized in normal use, including a neutral conductor but, by convention, not a PEN conductor’.

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in three-phase and single-phase three-wire circuits, where the size of the line conductors is less than or equal to 16 mm2 for copper, or 25 mm2 for aluminium, and

Typically, in the least complex domestic and similar premises, the current in the neutral conductor is equal to that in the line conductor. Regulation 524.2.1 requires that in single-phase, two-wire circuits, the neutral conductor should have a cross-sectional area (csa) not less than that of the line conductor in all cases.

●

where the neutral conductor carries current without a corresponding reduction in load current of the line conductors, typically in the presence of harmonics, and where the neutral conductor must take account the current-carrying capacity of the circuit, (523.6.3).

68 CPD Book PROFESSIONAL ELECTRICIAN

If the total harmonic content due to triplen harmonics is greater than 33 % of the fundamental line current, due to non-linear connected loads such as LED electronic convertors, variable speed drives, and uninterruptible power supply systems, an increase in csa of the neutral conductor may be required (524.2.2). It should be remembered that the current in the neutral conductor may be greater than that in any of the phase conductors due to the imbalance between the connected single-phase loads, caused by a combination of varying current demands and/or power factors in each phase. Additionally, consideration must also be given to overcurrent in the neutral

Fig 1. Thermal damage at terminations of EV charging equipment most likely caused by loose connections (image courtesy of Cenex, 2021)

conductor of a circuit (single-phase or three-phase) during an overload or short-circuit. However, it is permissible within a three-phase installation to have a neutral conductor with a reduced csa where each line conductor has a csa greater than 16 mm2 for copper or 25 mm2 for aluminium, and where the conditions of regulation 524.2.3 are met. Electrical connections Every connection between conductors or between a conductor and other equipment shall provide durable electrical continuity and adequate mechanical strength and protection (526.1). Inadequate connections made in current-carrying conductors, including a neutral conductor, can lead to an increase in resistance and a subsequent rise in temperature at the point of connection. Such conditions can pose a risk of thermal distress, damage to electrical equipment and/or its surroundings, or lead to a potential risk of fire. Poor connections can also increase circuit impedance, which may result in the failure of, or a delay in operation of, an overcurrent protective device under fault conditions. Arcing within an accessory or equipment resulting from a loose connection can also increase the risk of thermal damage. When a gap is formed between the points of contact within a poor connection an electric arc can develop. In such cases, a high-temperature discharge occurs in the form of hot plasma, created when electrical current ﬂows through the ionized air, between the contact points within the poor termination. Such high temperatures (in excess of 1,000°C) can lead to subsequent breakdown in both the conductive and insulating materials of the conductor or contact terminal allowing the formation of carbon deposits, which further exacerbates the thermal process. To better understand the potential heat generation that can be produced at a poor connection, consider the following example:

If the resistance of a defective connection between a neutral conductor and the terminal of the main switch of a consumer unit is found to be 2 Ω and the current ﬂowing in the neutral conductor is measured at 30 A, under these conditions, the heating power (P) generated at the connection would be:

construction of the installation and on completion of the work. Such routine inspection and testing aims to help identify any signs of wear, corrosion or loosening of connections before a dangerous situation arises, thereby mitigating the risk of thermal damage and/or fire.

P = I2 R 30 × 2 = 1800 W

Summary The neutral conductor is both a live conductor and a current-carrying conductor. It is crucial therefore that every connection, including that between neutral conductors and between a neutral conductor and equipment needs to be properly made, so that it provides durable electrical continuity and has adequate mechanical strength. In addition to the requirements for new installation work, a contractor carrying out electrical inspection and testing or maintenance within an existing installation should also take the opportunity to check the connections of not only line conductors but also those of neutral conductors.

This level of thermal energy is sufficient to cause significant damage and is potentially dangerous. Preventative measures and best practice It is important to maintain good working practices during installation work to ensure proper termination of electrical connections and equipment. The materials used for terminating such a connection must also be suitable for the intended application. Regulation 526.2 outlines the considerations for selecting the appropriate means of connection. There is a fundamental requirement within Section 134 of BS 7671 that every electrical installation is subjected to appropriate inspection and testing: ● ●

during construction, and on completion,

before it is put into service to confirm conformance to the relevant requirements of that standard (134.2.1). This is also supported by regulation 641.1 which also calls for inspection and testing to be carried out both during the

SECTION 4 ENDS! SCAN THE QR CODE TO CLAIM YOUR CPD CREDIT FOR THIS SECTION OR VISIT: WWW.RDR.LINK/EBX015 GET MORE DETAILS ABOUT NICEIC REGISTRATION AT: WWW.RDR.LINK/EBX016

PROFESSIONAL ELECTRICIAN CPD Book 69

SECTION FIVE

STAYING

ALIVE

roving dead eﬀectively and safely is vital when it comes to safe isolation and reducing the number of electricity-related injuries within the workplace. However, there are other hazards to factor in – like potential injuries caused by coming into contact with unexpectedly live metal parts.

Safe isolation process There has been significant activity from both electrical industry bodies and electrical test equipment suppliers, driving awareness around the subject of safe isolation. The process states that the relevant breaker or switch has to be identified, locked off correctly, tagged and the circuit verified dead before proceeding. For an effective safe isolation process it is key to ensure the correct equipment is available. Voltage Indicators (VI) must comply with legal safety standards, namely BS EN61243-3 and BS EN61010-1. Products such as Martindale’s VI13800 voltage indicator have been specifically designed to meet the standards. Also important is ensuring that the Lock out, tag out (LOTO) items available cover all potential isolation requirements. Generally, this would consist of a selection of MCB lock off devices, lock out tags, warning labels, padlock/s with a

70 CPD Book

PROFESSIONAL ELECTRICIAN

unique key/s, and a hasp if more than one person is working on a system. When the correct equipment is available and the electrical circuit is locked oﬀ, the basic proving dead process involves an initial prove, testing the VI against a proving unit to make sure it is working correctly. The next step is voltage test. The proved VI is used to check for dangerous voltage levels on the circuit to be worked on, whether single- or three-phase.

Steve Dunning, Managing Director of Martindale Electric, explains the hidden electrical dangers that can occur when they are not checked as part of the standard safe isolation process.

Finally, prove the VI against the proving unit again before starting to work on the circuit. This ensures the VI is functioning and working correctly to make sure that no damage has occurred, or fault has appeared, on your equipment. It is always recommended to use a dedicated proving unit matched to the VI to fully test that all LEDs on all ranges are working. A proving unit is safer than the mains and provides a live source wherever you are working.

Additional hazards Despite the rigorous process of safe isolation, other types of electrical hazards can still be present when working on electrical systems. One such issue is injuries caused to engineers, contractors, electricians, and others by encountering unexpectedly live metal parts including metal casings on equipment or appliances, pipework, plumbing, and other types of metalwork which should be earthed. This invisible danger can be present in any workplace situation ranging from simple domestic wiring through to commercial and industrial installations. There are many types of faults which can cause live metalwork, including: incorrect or hazardous wiring, trapped cables, and Protective Earth Neutral (PEN) faults. Widely discussed in the industry, the PEN fault is where a break or "open circuit" occurs in a PEN conductor which serves as both the neutral and protective earth. PEN conductors are generally present outside of an installation and are separated into a neutral and protective earth at the consumers supply connection, the split providing a safe local separate earth. The combined PEN conductor’s primary role is a return path for normal load current while also serving as the protective path for fault currents, ensuring that exposed conductive parts remain at or near-earth potential. A broken or faulty PEN conductor can cause dangerous voltages to appear on metalwork, creating an electric shock risk, ﬁre risk, and/or equipment damage. PEN faults in electrical supply systems can cause safety issues regarding electrical vehicle chargepoints; to combat this modern EV chargers should incorporate PEN fault protection. Further safety checks – touch voltage Touch voltage is the electrical potential diﬀerence between exposed metalwork and the earth due to a fault condition. The standard safe isolation process does not check for potentially live metalwork, so performing a touch test is an essential addition.

There are a number of tools available which are used for performing this test, primarily non-contact and single-pole contact indicators. Unlike a compliant safe isolation voltage indicator both require batteries and should always be fully checked for functionality prior to use. Non-contact voltage detectors should always be used with caution as they can often be sensitive to other signals such as static electricity. Care should also be taken regarding the voltage threshold of the indication to ensure that unsafe voltages can actually be detected. It’s also not possible to prove they are working correctly with a standard proving unit. Single pole contact indicators are a more reliable solution and can be incorporated into touch test safety procedures to help identify potential issues. For example, the Martindale VT7 is a single-pole contact voltage indicator which detects AC voltages of 50-600 V. This type of tester should always incorporate a self-test function and preferably be IP rated for indoor and outdoor use. Diverted current fault A diverted current fault occurs when electrical current flows away from its intended path due to damaged insulation, earth or neutral failure and other types of faults. This can create an abnormal current flow causing overheating, equipment damage, and potential electric shocks from unexpectedly live metalwork. While this fault is present the circuit may appear to be working correctly. Diverted current can be identified by checking for current flow, where appropriate, using a suitable clamp meter such as the Martindale CM79.

Measuring the earthing conductor while the circuit is supplying load can help identify diverted current. Low level leakage currents would be considered normal, but readings of several amps indicate a potential fault condition, possibly an open circuit PEN conductor. Safety first Safe isolation is neither complex nor costly but is vital for compliance with the Electricity at Work Regulations and for preventing harm. Locking off devices, using compliant voltage indicators, and proving dead with proving units are central to the process. Being aware of the risks associated with live metalwork is also key and, before working on any installation, precautions should be taken to identify hazardous touch voltages on exposed or extraneous metal parts. By embedding these procedures, workplaces can significantly reduce the risk of electrical accidents. Safety must always remain the priority, and the correct safe isolation procedure provides the foundation for protecting both people and infrastructure. There’s a wealth of online support materials to help generate safe electrical working procedures. The Martindale ALIVE campaign is a simplified and easy way to remember the process and assist with safe isolation implementation, while the “STOP. No Check. No Contact” covers the hazards associated with live metalwork. GET MORE INFORMATION ON MARTINDALE’S ALIVE CAMPAIGN BY VISITING: WWW.RDR.LINK/EBY014

PROFESSIONAL ELECTRICIAN CPD Book 71

NICEIC. The sign of a serious professional.

Q&A

NICEIC FAQs NICEIC’s team of team expert, engineers answeranswer essential questions from Each month, our of technical expert, technical engineers essential questions NICEIC-certified businesses. Here we share some of the latest queries. IURP 1Ζ&(Ζ& FHUWLȴHG EXVLQHVVHV Ȃ KHUH DUH WZR RI WKH ODWHVW TXHULHV Forare a new installation, any defect or omission revealed Q Q We working in a domestic apartment block

during thebeen inspection and testing shalltypes be? of and have questioned over the a) recorded on the EIC cable supports that we have installed. Within the communal area where a suspended ceiling is to be b) corrected installed, we have supported the cables using steel c) reported to customer ties to a cable tray system. Within the individual d) recorded as a “LIM” apartments, where a solid plasterboard ceiling is to be installed, we have used cable anchors and The answer is b) corrected ties. Should these also be steel ties? A plastic Regulation 644.1.1 states that “For a new installation, any A Regulation 521.10.202 requires that allinspection wiring and defect or omission revealed during the systems shall supported in such a way that, the testing shall bebe corrected before the Certificate is in issued”. HYHQW RI D ΋UH WKH\ ZLOO QRW EH OLDEOH WR SUHPDWXUH collapse and result in an entanglement risk. For compliance with BS 7671, can a 230 V AC fan be Q Typically, cables1 that installed above a installed for in Zone of a are domestic bathroom? plasterboard ceiling, it is likely that the means of a) Yes VXSSRUW ZLOO UHPDLQ H΍HFWLYH IRU ORQJ HQRXJK WR DOORZ b) No SHUVRQV WR HJUHVV WKH EXLOGLQJ DQG IRU ȴUHȴJKWHUV WR HQWHU WKH EXLOGLQJ DQG GHDO ZLWK WKH ȴUH HWF $OO WKH WLPH Thecables answer a) Yes areiscontained within the ceiling void, and A the the plasterboard is states intact, that they“In arezone protected Regulation 701.55 1, onlyfrom the the H΍HFWV RI KHDW DQG ȴUH following fixed and permanently connected equipment shall beininstalled, Itcurrent-using should also be noted that even the eventprovided of the it is suitable for installation in zone 1 according to thejoists, plasterboards failing, the cables will pass through manufacturer’s instructions:” and the list includes “(viii) where this is necessary for their routing, further limiting Ventilation equipment”. WKH OLNHOLKRRG RI WKHLU FDXVLQJ DQ HQWDQJOHPHQW ULVN )RU WKHVH UHDVRQV WKH XVH RI SODVWLF WLHV RU FOLSV LQ D ȵRRU Therefore, as the fan would fall within the definition of YRLG DERYH D SODVWHUERDUG FHLOLQJ LV DFFHSWDEOH

installation would be compliant Q ventilation We have equipment, been askeditsto install some additional providing the existing manufacturer confirms thataitschool. is suitable lighting on circuits within All for of installation within zone 1 of a bathroom and the fan has a the additional lighting will be installed using minimum degree of protection of IPX4 against external surface-mounted conduit. However, the existing influences. circuits that we are extending are wired using thermoplastic insulated andissheathed The required external influence specified incables regulation buried in the walls. Do we need upgrade the 701.512.2 which states that “Installed to electrical circuits toshall include equipment have additional at least the protection? following degrees of protection: (i) In zone 0: IPX7 (ii) In zones and 2: IPX4”. A The alterations/additions that you are 1undertaking

on the existing circuit(s) would need to meet the requirements of BS 7671 (641.5). What is the minimum size of a supplementary bonding conductor if mechanical protection not provided? However, this would not necessarilyisrequire the 2 existing circuit to be upgraded, provided that there a) 2.5 mm ZHUH QR GHIHFWV RU RPLVVLRQV WKDW ZRXOG D΍HFW WKH b) 4.0 mm2 VDIHW\ RI \RXU DOWHUDWLRQV RU DGGLWLRQV c) 6.0 mm2 $Q\ GHIHFWV LGHQWLȴHG RQ WKH H[LVWLQJ FLUFXLWV WKDW d) 10.0 mm2 ZRXOG QRW D΍HFW WKH VDIHW\ RI \RXU SODQQHG ZRUNV

2 answer is b) 4.0the mmrequirements in accordance with of regulation A The

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6HH DOVR WKH DUWLFOH LQ WKLV LVVXH RQ DGGLWLRQV Regulation 544.2.1 states that “A supplementary bonding DQG DOWHUDWLRQV VHH /HWȇV JHW WHFKQLFDO S conductor connecting two exposed-conductive-parts shall have a conductance, if sheathed or otherwise provided with mechanical protection, not less than that of the smaller protective conductor connected to the exposed-conductive-parts. If mechanical protection is not provided, its cross-sectional area shall be not less than 4 mm”.

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THE

CODEBREAKERS THOMAS HILL: WE HAD A PROBLEM WITH SOME SOCKETS NOT WORKING ON A RECENT JOB. I REMOVED THE BOARD COVER AND FOUND THIS… Fault finding is often the result of a lack of regular inspection and testing of an electrical installation, or, as in this case, additional external influences affecting the integrity of the installation. It is evident that there has been intrusion by mice, where they have been chewing on the single insulated conductors as they enter the RCBOs, which has resulted in contact between the live conductors, leading to the demise of the creature and the operation of the RCBO. Although the RCBO of the socket-outlet circuit has alerted the owner that there is a fault, you can see there is further damage to other circuit conductors, which remain energised. The consumer unit also appears to have suffered some distortion, either as a result of the short-circuit or from poor original installation. Remedial work may involve re-terminating the conductors or might even lead to a partial or full rewire, or at the very least a further investigation for vermin damage to the cables installed within the installation. While not strictly an electrical issue, the property owner would need to tackle the vermin infestation prior to the remedial works being carried out or the same outcome would likely occur again.

Therefore, the appropriate classification code would be a C2, Potentially dangerous, urgent remedial action required due to the damage to the circuit conductors and further damage within the cabling of the installation.

74 CPD Book PROFESSIONAL ELECTRICIAN

ANDRIY BURLAKA: INTERESTING USE OF THE EARTH ON THIS ONE!

When undertaking periodic inspection and testing, part of the procedure involves carrying out sample inspections of accessories. In this case, the sample revealed a failure in the understanding of correct conductor selection. A circuit protective conductor (cpc) shall only be used for the purpose of earthing. It must not be used for other purposes and must never be oversleeved or re-identified as a live conductor. In this situation the bare cpc of a pvc/pvc cable has been utilised as a switch wire, which introduces further issues. The cable is then provided with only basic insulation, rather than the insulated and sheathed protection provided by the red and black conductors. This appears to be the result of non-compliant work, where either two way switching has been

introduced or an additional switch wire was required, instead of installing new cabling. The absence of a cpc at the metallic light switch and other metallic lighting points introduces a potential risk of electric shock in the event of a fault. Therefore, the appropriate classification code would be a C2, Potentially dangerous, urgent remedial action required due to potential damage to the conductors and the lack of cpc for the lighting circuit accessories.

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SECTION FIVE

IMPEDANCE AND ITS IMPACT ON VOLTAGE DROP IN CABLES This article from the experts at NICEIC examines impedance, and more specifically, considers its impact on voltage-drop in cables when supplying electrical loads having a poor power factor. This will be demonstrated with a practical example. It is worth noting that such considerations are rarely required in a domestic dwelling where most cable sizes are typically less than 16 mm2. It may be useful to refer to Appendix 4 of BS 7671 when working through the examples given in this article. Impedance v Resistance Resistance is a property that opposes the flow of current. In a direct current (DC) circuit under steady-state conditions, resistance is the only opposition to current flow. However, when considering an alternating current (AC) in a circuit, it should be remembered that other factors such as the effects of inductance and capacitance must also be considered. The influence of inductance and/or capacitance on a circuit is dependent on the supply frequency. The term ‘reactance’ is used to describe these effects, which can be either inductive or capacitive. Key terms: Resistance, Reactance, and Impedance Further consideration of the terms resistance, reactance and impedance include:

impose changes in current or voltage. Reactance exists wherever there are magnetic (inductive) or electrostatic (capacitive) fields, in which its value depends on both the inductance/capacitance elements, and the frequency of the supply. If a circuit containing only reactance was connected to an AC supply, the effect of the rate of change of supply voltage would cause the circuit current to either lag or lead the voltage by 90o depending on whether the element is inductive or capacitive respectively. ● Impedance (Z): measured in ohms (Ω) is the total opposition to current flow in an AC circuit containing both resistance and reactance. This can be determined using the equation: Z = √R2 +X 2

● Resistance (R): measured in ohms (Ω) is an inherent property of all conductors. When alternating current passes through a resistance, it causes a voltage-drop that is in-phase with the current. ● Reactance (X): measured in ohms (Ω) is the opposition on circuit elements, such as in capacitors and inductors, to

76 CPD Book PROFESSIONAL ELECTRICIAN

“When alternating current passes through a resistance, it causes a voltage-drop that is in-phase with the current.”

Fig 1. Impedance triangle showing relationship between circuit components and power factor

Impedance is present in most circuits supplied from an AC source. As such, the current flowing through an impedance will be out of phase with the supply voltage by an angle between 0o and 90o. The power factor of the circuit can be determined using the trigonometry ratio: cosϕ = R Z The relationship between these three terms is shown in the impedance triangle of (Fig 1). In order to establish the design current (Ib) for a specific circuit, the impedance must be determined. The design current can be found using: Ib= Uo Z

Distribution and circuit cables In cable analysis, each line conductor of the distribution or circuit cable can be modelled as having a series resistance R and an inductive reactance XL, as shown in the single-line diagram of (Fig 2).

tabulated (mV/A/m)z values should be used (see Equation 1).

Fig 2. Line diagram showing the component parts of a cable

Capacitive reactance XC is generally a concern for parallel conductors operating at high voltage and over longer distances, such as transmission cables. Such effects are negligible for distribution and circuit cables and are therefore not shown in Fig 2. Where circuit cable conductors exceed 16 mm², which is common in distribution circuits used in industrial or commercial type installations, the tables for current-carrying capacity and voltage-drop in Appendix 4 of BS 7671 give separate values of voltage drop per ampere per metre (mV/A/m) for r, x and z. The intention of BS 7671 in providing individual values of r, x and z in these tables is to allow for an accurate assessment of voltage-drop to accommodate loads having a large inductive element, for example induction motors or capacitive elements, such as those providing noise ﬁltering within electronic equipment. Generally, most connected loads will be inductive in nature. Appendix 4 of BS 7671 recognises, in paragraph 6, that where there is power factor in a circuit, the use of the tabulated values of mv/A/m may lead to a calculated value of voltage drop which is higher than the actual value. Where the power factor of the load is not known, the

“When carrying out circuit design, using the load power factor will provide a more accurate value...”

However, if the load power factor is known, then using the tabulated (mV/A/m)r and (mV/A/m)x values will provide a more accurate assessment of voltage-drop (see Equation 2). See also (paragraph 6) of Appendix 4 of BS 7671. When carrying out circuit design, using the load power factor will provide a more accurate value and will in most cases result in a smaller conductor size. Example Consider a 100 kVA three-phase induction motor having a design current (Ib) of 144 A with a power factor of 0.75 lagging and cable route length of 120 m. From Table 4H4A a 70 mm2 aluminium cable has been selected and from Table 4H4B column 4, the mV/A/m values are: r = 0.90, x = 0.14 and z = 0.92. Assuming no other factors apply, determine the volt-drop in the supply cable. 100 ×103 The design current (Ib) = = 144 A √ 3×400 (i) If the power factor was not known, equation 1 would be used: voltage drop= 0.92 x 144 x 120 = 16 V 1000 (ii) If the power factor is known, equation 2 would be used (see Example 2). Table 4Ab in Appendix 4, recommends that the maximum voltage drop from the origin of the installation to the point of utilisation should not exceed 5 % of the nominal supply voltage1 this equates to 20 V (5% of 400 V). 1

“Capacitive reactance Xc is generally a concern for parallel conductors operating at high voltage over longer distances, such as transmission cables.” If, for illustration purposes, 5 V of this permitted 20 V allowance is assumed to have been dropped upstream in the distribution cable, then using equation 1 (z value), the calculated voltage drop for the final circuit is 16 V, giving: 5 + 16 = 21 V (exceeds the 20 V limit) This would indicate that the chosen conductor is undersized and that a larger conductor CSA is required to achieve conformance. However, using equation 2 (r and x values with known power factor) gives 13.3 V for the final circuit, resulting in a voltage drop of: 5 + 13.3 = 18.3 V Using equation 2 demonstrates that the ﬁnal circuit would conform without unnecessarily upsizing the conductor CSA when the load power factor is known. Summary This article has used a practical example to help examine the impact of impedance on voltage-drop in circuit cables, particularly when supplying electrical loads with poor power factor. For large industrial type installations, using the known power factor in voltage-drop calculations often yields a more accurate result, allowing the selection of a smaller CSA of conductor size while optimising cable design and reducing installation costs. GET MORE DETAILS ABOUT NICEIC REGISTRATION AT: WWW.RDR.LINK/EBY012

Section 525 also gives a number of examples of where the volt-drop limits in Appx 4 may be exceeded.

PROFESSIONAL ELECTRICIAN CPD Book 77

SECTION FIVE

REPORTING FROM THE FIELD Jonathan Swain, Technical Writer at NAPIT, discusses the oftenoverlooked skill of completing an Electrical Installation Condition Report (EICR) accurately and professionally.

he completion of an EICR can be daunting. Few of us chose this career for our love of paperwork. This article focuses on the actual completion of the report, see Fig 1. While less glamorous than other aspects of the inspection process, accurate and consistent documentation is equally important. The report tells the story of the installation, and the clearer the story is, the better understood, and safer the installation will be throughout its service life. Along the way, we’ll share tips and feedback from NAPIT members and field officers to highlight the difference a NAPIT-certified inspector can make, and address some of the common mistakes. When completing an EICR form, Section A records client and installation details and Section B states the reason for the report. These are generally straightforward, but should be completed carefully to ensure accuracy – especially Section B, as it provides context for the decisions recorded later. Since these first sections are usually simple, we’ll move on to a part that is often overlooked.

the original and newer parts to obtain an accurate report. If no records are available, sampling could be inappropriate, there’s nothing to compare to, and 100% inspection and test may be required, with no limitations. Ironically “100% of the installation” is one of the most common statements that we see recorded in Section D, often followed by “None” under limitations, see Fig 3. While not impossible, this is highly unlikely (and risky). From both a moral and ﬁnancial liability perspective, this section is critical.

Section C Section C informs and justiﬁes the extent and agreed limitations of the inspection, as displayed in Fig 2. For example, if an installation has been added to, it’s important to carry out suﬃcient inspection and testing for both

PROFESSIONAL ELECTRICIAN CPD Book 79

SECTION FIVE

NAPIT Technical Tip: Any agreed limitation must be discussed and agreed with the client or person ordering the work in advance. A site survey provides the perfect opportunity for this discussion, with limitations clearly stated in the quotation.

“Accurate documentation is essential because future inspections may rely on your stated scope.”

Why limitations matter Periodic inspection and testing presents a unique challenge: the inspector is assessing an installation they did not install and can only work with the information available. There will always be limitations when inspecting a completed installation in a finished building already in use. Failing to record these limitations accurately can result in an incomplete picture and increase risk of unassessed hazards.

NAPIT Technical Tip: The idea that “If it complied when installed, it can’t be dangerous now” is false. The Inspection must be based on the current edition of BS 7671, including amendments or corrigendums. Non-compliances do not necessarily mean danger, but it can.

Section D Section D acts as a contract (see Section G declaration), clearly defining the scope of the report and what was inspected and tested. Unexpected issues or operational limitations can be also noted here, allowing all parties to decide if further action is needed. Accurate documentation is essential because future inspections may rely on your stated scope. NAPIT Technical Tip: Clear sampling and agreed limitations help inspectors stay focused on-site. If issues arise, you can adjust the sample rate and invoice separately for the additional work. Incorrectly claiming that 100% of the installation was inspected and tested with no limitations could lead to a flawed condition report.

80 CPD Book PROFESSIONAL ELECTRICIAN

Section E Too often, Section E is filled with a simple ‘satisfactory’ or ‘unsatisfactory’, which is redundant, as the inspector declares this in the overall assessment line directly below. Instead, think of Section E as your opportunity to summarise the condition of the installation in plain language, see Fig 4. This gives the client a clear overview without the heavy technical detail found elsewhere. Ask yourself: ‘If I were explaining this in conversation, what would I say?’

Section F The purpose of periodic inspection and testing is to identify defects and non-compliances that could present a risk to people, livestock and property. This must be done often enough to ensure unreported danger is minimised or (ideally) non-existent. At periodic inspection this recommendation is the inspector’s responsibility and should be recorded and justified in Section F, an example of this is shown in Fig 5. While generic intervals (e.g. 5 years for commercial, 10 years for domestic) are widely used, each installation must be individually assessed. The reason for producing the report (Section B) may also be important here as there may be statutory requirements to be considered, for example private and social housing sector legislation. There may also be requirements from other interested parties such as insurers and licensing authorities that will inform the recommendation. Use your professional judgment, based on the condition found and the utilisation of the installation, to recommend an appropriate interval. Part 3 of the NAPIT Codebreakers publication, particularly table 3.5 (see Fig 6), provides a risk-based approach with three interval options depending on the levels of control and maintenance. The key question is: how long are you comfortable leaving it, and why? Section K Sections G, H and I are straightforward so we will now move on to the final section of the form, Section K.

“The so-called “EICR race to the bottom” is driven by cost-cutting agents, unscrupulous contractors and landlords treating the process as a box-ticking exercise.” 2) Underlying design flaws remain unreported and unaddressed 3) Repairs may not be contractually agreed, risking non-payment 4) A conflict of interest may arise if the inspector is also paid for remedial action whilst carrying out the inspection 5) It distracts from the inspection itself In short: the correct process is to issue an “Unsatisfactory” report, then provide certificates for any agreed remedial work. Where necessary, an Installation Safety Record Summary or Landlords Electrical Installation Safety Record can also be completed to clearly demonstrate that all necessary action has been taken.

Section K is where you document any observations coded on the schedule of inspections or schedule of test results, see Fig 7. Each observation should be clearly described, with its location specified so future inspectors or contractors can easily identify it. NAPIT Technical Tip: Testing faults can also be listed here, the wording at the top of Section K includes schedule of test results. Just refer to that. Whilst we will not be considering coding specifically in this article, when coding, the inspector must make a valid and justifiable assessment of risk using their own knowledge and experience alongside current industry guidance.

It can be useful to qualify the decision (see the completed example), particularly where an observation is not clear cut and requires some explanation as to why a code has been selected. NAPIT Technical Tip: The report is not a quote. Observations like ‘needs new fuseboard’ are inappropriate. The inspector’s role is to find the issue, not design or carry out the solution. Avoid silent repairs Some contractors are asked to fix issues on the spot to produce a “Satisfactory” report. This is problematic because: 1) Any ‘work’ must be properly certificated (electrical installation or minor works certificate)

NAPIT Technical Tip: A known fault should not be coded “Further Investigation” (FI), it is already known. Fault-finding may form part of the remedial process, but the report should reflect the observed danger and be suitably coded. Raising standards The so-called “EICR race to the bottom” is driven by cost-cutting agents, unscrupulous contractors and landlords treating the process as a box-ticking exercise. An EICR is a safety-critical document that demands experience, knowledge and sound judgement, and the ability to record scope and findings with accuracy. Hopefully, these insights help you produce reports that not only comply with requirements, but also reflect the professionalism and expertise expected of a NAPIT-certified inspector. FOR MORE INFORMATION ON NAPIT REGISTRATION VISIT: WWW.RDR.LINK/EBY015

PROFESSIONAL ELECTRICIAN CPD Book 81

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SECTION XXXXXXX FIVE

THE

RULE

John Hayhurst, Electrical Tutor at City Skills SCC, takes a closer look at the ‘20% rule’, its purpose, application and common misinterpretations.

ost electricians are confident they understand the 20% rule. It is familiar, widely taught, and routinely applied when assessing earth fault loop impedance. For many, its use has become almost automatic when reviewing measured R1 + R2 values or comparing results with the tabulated Zs values in the On-Site Guide. But what if that assumption is wrong? If the allowance is being applied incorrectly, cables may be oversized unnecessarily, costs increased, and circuit design constrained without a good technical reason. Understanding what this so-called “rule of thumb” is actually for could change the way your circuits are designed and assessed.

What is the 20% allowance actually for? The 20% factor is often described as a correction for increased conductor temperature during an earth fault. While conductor resistance does vary with temperature, faults cleared by overcurrent protective devices often occur too quickly for significant heating to take place during the fault itself. The allowance is better understood as a margin for uncertainty, accounting for factors such as: ● Variations in ambient and operating temperature ● Contact resistance variability

● Workmanship ● Ageing and deterioration ● Changes in bonding and fault paths over time It represents the diﬀerence between values measured under controlled test conditions and the impedance that may exist under less favourable, real-world conditions throughout the service life of an installation. Crucially, these uncertainties arise not from the test method itself, but from how installations behave and change once they are in service. Zs, R1 + R2, and where the allowance really applies The On-Site Guide implies that the 20% allowance is applied to Zs because Zs represents the complete earth fault loop and determines disconnection performance. While Zs is indeed the parameter assessed for compliance, the technical basis for the allowance lies primarily within the installation wiring. The factors the allowance is intended to address – temperature variation, contact resistance, ageing, and workmanship – aﬀect the circuit conductors represented by R1 + R2, not the external supply. The allowance arises because of the parts of the system that are subject to deterioration and variability over time. Why Ze is excluded Although Ze can change over time due to

variations in the supply network and external earth paths, this variability is not what the 20% allowance is intended to address. Changes in Ze are just as likely to improve as they are to worsen, as network impedance is inﬂuenced by upgrades, alterations, loading conditions, and environmental factors such as weather. By contrast, the resistance of installation conductors represented by R1 + R2 can generally only increase over time. For this reason, Ze is treated as a measured condition at the time of veriﬁcation, while the allowance is directed at uncertainty within the installation wiring. This misunderstanding is reinforced not only by how the allowance is described in the On-Site Guide, but also by how the calculation is written and interpreted. A common calculation error: the order of operations A further problem arises not only from where the 20% allowance is applied, but how it is applied mathematically. The earth fault loop impedance is sometimes calculated using an expression written as: Zs = Ze + (R1 + R2) × 1.2 Written this way, the calculation is ambiguous. Some calculators process calculations strictly from left to right, while others apply standard order-of-operations rules (BODMAS/BIDMAS). As a result, the

PROFESSIONAL ELECTRICIAN CPD Book 83

SECTION FIVE same values can produce different answers, depending on the calculator or software used. If the multiplication is applied to the sum of Ze + R1 + R2, the result does not reflect the intent of the 20% allowance and introduces an error. To eliminate this problem, the calculation must be written unambiguously as: Zs = Ze + ((R1 + R2) × 1.2) The brackets make it clear that the 20% allowance applies to the R1 + R2 value and not to the sum of these ohmic values. This highlights that misunderstanding the allowance is not only a conceptual issue, but also a practical one rooted in poor notation and calculation practice. Measured R1 + R2 values and the limits of testing Continuity testing is carried out with conductors at or near ambient temperature, using low test currents and generally with the installation unloaded. Under these conditions, R1 + R2 testing confirms that the circuit protective conductor is present, continuous, and reasonably sound at the time of testing. What it does not do is replicate fault conditions in service. While conductor temperature will certainly increase during a fault, the degree of increase depends on the nature of the fault, the protective device, the installation method, and the fault location. For this reason, R1 + R2 values should be recorded exactly as measured. They should not be artificially increased by applying a 20% factor. Where the allowance is relevant The 20% allowance is relevant when considering Zs as a whole, because Zs represents the complete earth fault loop under fault conditions and includes all conductive paths that may influence fault current return in practice. This does not imply that protective bonding conductors are intended to act as circuit protective conductors as, under normal circumstances, fault current returns via the CPC associated with the circuit. However, in real installations, parallel or incidental earth paths can exist through bonded extraneous-conductive-parts, structural metalwork, or interconnected services.

84 CPD Book

PROFESSIONAL ELECTRICIAN

Although these paths are not relied upon by design, their presence – and their variability over time – can influence the effective earth fault loop impedance. When it is reasonable not to apply the 20% allowance There are circumstances where applying the 20% allowance adds little or no technical value because the conditions it is intended to address are unlikely to arise. The allowance exists to account for uncertainty over time, but where the earth fault path is simple, stable, and predictable, measured values can be a reliable representation of in-service conditions. In such cases, applying a blanket margin risks substituting arithmetic for judgment. It is therefore reasonable not to apply the allowance where installation characteristics indicate that deterioration, alteration, or variability in the fault path is unlikely to develop to a degree that would affect disconnection performance. This does not remove the need for compliance; instead it recognises that conservatism must be proportionate to risk. A common example is a dedicated radial circuit supplying a single fixed item of equipment, such as a water heater, pump, or packaged plant. These circuits typically have few terminations, no intermediate accessories, stable load characteristics, and a low likelihood of future alteration. Where measured Zs values are comfortably within limits, the fault path is predictable and unlikely to deteriorate significantly. Similarly, circuits forming part of a recent installation may justify reliance on measured values alone. Where terminations

have been made to manufacturer torque requirements, inspection confirms good workmanship, and there has been no opportunity for ageing or disturbance, the factors the allowance addresses have not yet developed. Circuits installed in controlled, low-stress environments – such as plant rooms or service risers – are also less likely to experience increasing contact resistance or degradation over time due to minimal vibration, thermal cycling, and mechanical disturbance. Finally, where a circuit is protected by an RCD, and Zs is not the parameter determining disconnection time, applying an allowance to Zs provides no meaningful improvement in safety assessment. Provided RCD performance is verified, reasonable variations in loop impedance do not affect disconnection. In all of these cases, the common factor is predictability. Where the earth fault path is simple, stable, and unlikely to change, reliance on measured values without applying the 20% allowance can be technically defensible, provided the decision is informed, justified, and appropriately recorded. The role of professional judgement The 20% allowance is not mandatory arithmetic. It is an engineering margin intended to support professional judgement, not replace it. Used appropriately, it strengthens conservative assessment under worst-case assumptions. Used indiscriminately, it risks becoming a procedural shortcut that either conceals genuine issues or introduces unnecessary correction where none is warranted.

Competent assessment requires understanding why the allowance exists, where it should be applied, and when it may reasonably be set aside. The 20% allowance and EICR coding During an Electrical Installation Condition Report (EICR), measured values are assessed against the requirements of BS 7671 to determine whether the installation is safe for continued use. In this context, the 20% allowance is often misunderstood as a trigger for coding, particularly where measured values are close to maximum permitted limits. It is important to recognise that the 20% allowance is a design and assessment margin, not a defect threshold. A measured value that falls within the recognised allowance, and still meets the required disconnection times, does not in itself represent a departure from the Regulations. Where measured Zs values comply with the applicable maximum values and there is no evidence of deterioration, overheating, loose terminations, or poor workmanship, there is no technical basis

for assigning a code solely because the result is “within the 20%”. A C3 (Improvement Recommended) may be appropriate only where professional judgement indicates a reasonable likelihood that future deterioration could lead to non-compliance. This might include situations where measured values are close to the limit and are combined with observable factors such as ageing, mechanical stress, vibration, repeated thermal cycling, or environmental conditions likely to increase resistance over time. In such cases, the code is justified by the condition and predictability of the installation, not by the numerical result alone. The recommendation reflects prudent risk management rather than an existing safety issue. Conversely, assigning a C3 solely because a measured value lies within the 20% allowance risks conflating conservative assessment with defect identification. This approach can lead to defensive coding and inconsistent reporting, neither of which improves safety or clarity.

Conclusion The widespread practice of applying the 20% allowance directly to measured R1 + R2 values reflects a misunderstanding of its purpose. The allowance exists to address uncertainty in real installations when assessing Zs, not to correct individual resistance measurements. Circuit length alone does not determine whether the allowance should be applied. Predictability, variability, and the likelihood of change over time are the governing considerations. Understanding these distinctions leads to more meaningful interpretation of test data, better use of professional judgement, and more reliable long-term fault protection.

SECTION 5 ENDS! SCAN THE QR CODE TO CLAIM YOUR CPD CREDIT FOR THIS SECTION OR VISIT: WWW.RDR.LINK/EBY045

THE

CODEBREAKERS BRUCE FERROSSA: NO, YOUR EYES ARE NOT DECEIVING YOU, THAT REALLY IS ELASTOPLAST... JUST IN CASE THE CABLES GET HURT... HMMM!!! THIS BOARD WAS ONLY FITTED AROUND A YEAR AGO. For electrical installations to comply with BS 7671, Regulation 134.1.1 requires that good workmanship and proper materials shall be used in the erection of installation. As part of the initial verification, and before being put into service, the installation must be appropriately inspected and tested to verify that it meets the requirements of BS 7671. It is often surprising the extent to which some installers will go to, in order to complete work without meeting these fundamental requirements. In this case there is no justification for the use of materials such plasters when a wide range of proprietary accessories are available to protect cables against abrasion from the sharp edges of consumer units, distribution boards and associated equipment. Although the plaster may provide some level of protection, it is not designed for this purpose. It should therefore be a recommendation to replace with a product meeting the appropriate product standards. Another consideration in this scenario is the excessive aperture in the base of the consumer unit/distribution board. This is likely to exceed IP2X, potentially allowing access to live parts. Therefore, the appropriate classification code would be a C3 improvement recommended for the unsuitable material providing abrasion protection but also a C2, Potentially dangerous, urgent remedial action required due to the excessive hole exceeding IP2X.

86 CPD Book PROFESSIONAL ELECTRICIAN

MARTYN GUEST: A LITTLE LATE, BUT I FOUND THIS WHEN STARTING A REWIRE A FEW YEARS AGO. IT TOOK ME A WHILE TO WORK OUT WHY THE SOCKETS REMAINED LIVE AFTER TURNING OFF EVERY MCB! Every electrical installation requires overcurrent protective devices to provide protection against fault currents. A range of device types are, and have been, available that meet these requirements. Electrical contractors must not alter the characteristics of an item of equipment that meets the appropriate product standards. This dangerous modification is shown, where a section of wire (which does not appear to be a fuse wire), has been used to bypass the operation of the protective device. This presents a significant risk of electric shock and fire within the premises. This appears to be a case of a failed protective device where the person carrying out the repair either did not have, or could not obtain, a suitable replacement and instead carried out a potentially lethal modification. A homeowner or tenant would be unaware that the socket-outlet circuits are no longer provided with overcurrent protection. Therefore, the appropriate classification code would be a C2, Potentially dangerous, urgent remedial action required due lack of overcurrent protection. If a C1 Danger present, Risk of injury, Immediate remedial action is required, was applied it would also be justified.

ORDER YOUR COPY OF NAPIT CODEBREAKERS BY VISITING: WWW.RDR.LINK/EBZ013

NICEIC. The sign of a serious professional.

Q&A

NICEIC FAQs Each month, our of technical expert, technical engineers essential questions NICEIC’s team of team expert, engineers answeranswer essential questions that have IURP 1Ζ&(Ζ& FHUWLȴHG EXVLQHVVHV Ȃ KHUH DUH WZR RI WKH ODWHVW TXHULHV been put to them by NICEIC-certified businesses. Let’s take a look at some of the latest queries. Q We are working in a domestic apartment block

and have been questioned over the types of cable supports that we have installed. Within the ‘An overcurrent occurring in a circuit which is Q communal area where a suspended ceiling is to be electrically sound’ is the BS 7671 definition of installed, we have supported the cables using steel what? ties to a cable tray system. Within the individual apartments, where a solid plasterboard ceiling is be installed, we have used cable anchors and Overload current A to plastic ties. Should these also be steel ties?

Q We have been asked to install some additional

Q A

on theof existing circuit(s) would need to meet the more the following: requirements of BS 7671 (641.5).

systems shall be supported in such a way that, in the HYHQW RI D ΋UH WKH\ ZLOO QRW EH OLDEOH WR SUHPDWXUH Overcurrent collapse and result in an entanglement risk.

However, this would not necessarily require the

A current exceeding the rated value. For

It should also be noted that even in the event of the Fault currentfailing, the cables will pass through joists, plasterboards where this isresulting necessary from for their routing, further limiting A current a fault. WKH OLNHOLKRRG RI WKHLU FDXVLQJ DQ HQWDQJOHPHQW ULVN )RU WKHVH UHDVRQV WKH XVH RI SODVWLF WLHV RU FOLSV LQ D ȵRRU YRLG DERYH D SODVWHUERDUG FHLOLQJ LV DFFHSWDEOH

BS 7671 regulation 543.2.1 states that:

A AThe alterations/additions are undertaking protective conductor that mayyou consist of one or

Part 2 Definitions in BS 7671 gives the following definitions: A Regulation 521.10.202 requires that all wiring

Typically, for cables that are installed above a conductors the rated value is the current plasterboard ceiling, it is likely that the means of carrying capacity. VXSSRUW ZLOO UHPDLQ H΍HFWLYH IRU ORQJ HQRXJK WR DOORZ SHUVRQV WR HJUHVV WKH EXLOGLQJ DQG IRU ȴUHȴJKWHUV WR Overload current HQWHU WKH EXLOGLQJ DQG GHDO ZLWK WKH ȴUH HWF $OO WKH WLPH the are contained withinin theaceiling and is Ancables overcurrent occurring circuitvoid, which the plasterboard is intact, they are protected from the electrically sound. H΍HFWV RI KHDW DQG ȴUH

lighting on existing circuits within a school. All of the additional lighting will be installed using Can a 10 mm² aluminium single core cable be surface-mounted conduit. However, the existing used as a protective conductor? circuits that we are extending are wired using thermoplastic insulated and sheathed cables buried in the walls. Do we need to upgrade the No circuits to include additional protection?

(a) A single-core existing circuit to becable upgraded, provided that there ZHUH QR GHIHFWV RU RPLVVLRQV WKDW ZRXOG D΍HFW WKH (b) A conductor in a cable VDIHW\ RI \RXU DOWHUDWLRQV RU DGGLWLRQV (c) An insulated or bare conductor in a common $Q\ GHIHFWV LGHQWLȴHG RQ WKH H[LVWLQJ FLUFXLWV WKDW enclosure with insulated live conductors ZRXOG QRW D΍HFW WKH VDIHW\ RI \RXU SODQQHG ZRUNV (d) A fixed bare or insulated conductor

VKRXOG EH UHFRUGHG RQ WKH FHUWLȴFDWLRQ SURGXFHG in accordance with the requirements of regulation A 6HH DOVR WKH DUWLFOH LQ WKLV LVVXH RQ DGGLWLRQV protective conductor of the types given in DQG DOWHUDWLRQV items (a) to (d) VHH /HWȇV JHW WHFKQLFDO S of Regulation 543.2.1, which

includes single core cables, having a cross-sectional area less than or equal to 10 mm2 must be of copper (543.2.4).

If you are an NICEICFHUWLILHG EXVLQHVV ORRNLQJ for convenient CPD resources, scan the QR FRGH IRU PRUH LQIRUPDWLRQ

SECTION SIX

CABLE CALCULATIONS – WORKED EXAMPLES Jake Green, Head of Technical Engagement at Scolmore Group, provides the second of several articles looking at the process of determining suitable cable sizes for an electrical installation.

n this article a worked example of a single-phase circuit will be used to demonstrate the basic process used to calculate a suitable cable size.

temperature is 1.0 Cable SWA to BS 5467. 1) Design current Ib =

Example An air-source heat pump (ASHP) having a rating of 7.6 kW, 50 Hz, 230 V AC is to be installed in a dwelling. The circuit is to be wired in steel-wire armoured (SWA) cable conforming to BS 5467 and is surface mounted on a masonry wall and grouped with one other circuit. It is to be assumed that the ambient temperature is 30°C. The length of run between the consumer unit and ASHP is 28 m. The local consumer unit contains circuit-breakers conforming to BS EN 60898. The Earthing system is TN-C-S having a measured external earth fault loop impedance of 0.2 Ω. The measured prospective short-circuit current is 5 kA.

The basic process is as follows: From Table 4A2 Appendix 4 BS 7671, the Installation Method is C (multi-core cable ﬁxed on or spaced less than 0.3x cable diameter from a masonry wall). From Table 4C1 Rating factor for grouping is 0.8 From Table 4B1 Rating factor for

7600 P = = 33.04 A U0 230

2) Select a suitably rated overcurrent protective device In ≥ Ib In = 40 3) Determine cable cross-sectional area It =

40 In = = 50 A 0.8×1 Cg Ci

4) Select a cable cross-sectional area of suﬃcient size to carry 50 A. Reference Column 2 1 two-core cable, single phase. Table 4D4A Appendix 4 BS 7671 since the conductor operating temperature is 70 °C. (Strictly speaking Table 4E4A should be referenced for cables to BS 5467, however since the temperature is limited Table 4D4A is used). 10 mm2 cable carries 67 A. 5) Determine voltage drop. From Table 4D4B column 3 10 mm2 has a voltage drop of 4.4 mV/A/m. Vd =

mV/A/m×Ib×l 1000

4.4×40×28 = 4.9 V 1000

Refer Regulation Group 525 and Clause 6.4 Appendix 4 BS 7671. Permitted voltage drop is 5% of nominal voltage (230 V). This allows for a maximum 11.5 V. This calculation confirms that a SWA cable of cross-sectional area 10 mm2 has sufficient current-carrying capacity and a low enough voltage drop. Determining the size of the circuit protective conductor. Where the protective measure is Automatic Disconnection of Supply (ADS), further consideration will need to be given to whether, or not, the selected protective device will operate within the time permitted by Table 41.1 for a TN system. Table 41.1 requires that the selected protective device must operate within 0.4 s (Regulation 411.3.2.2 refers). It is permitted for the armouring of a SWA cable to be used as a circuit protective conductor. Indeed, it is a rare typical circuit in which the armouring is insuﬃcient in size. In subsequent articles we will consider how to determine the earth fault loop impedance of a circuit. Conclusion The cable calculation process is methodical and to be undertaken in a set order. Time taken in ordering data at the start of the process will aid the electrical professional in ensuring errors are eliminated.

PROFESSIONAL ELECTRICIAN CPD Book 89

SECTION SIX

WHY DO LED LIGHTS FLICKER?

ver had a “simple job” turn into a major headache? A few years ago, a ROBUS team member was troubleshooting flickering on a ground-floor lighting circuit. After hours of fault-finding, the cause turned out to be a poor connection amongst a group of downlights hidden above the ceiling and tied into the same run! It later became clear they’d been deliberately concealed to increase the dimmer load and bring it into its compatible range. The client didn’t even realise those hidden lights were drawing an extra 50 W – with no usable light to show for it. It’s an unusual fault, but it highlights something important: flicker isn’t always where you expect it to be, and without a

90 CPD Book PROFESSIONAL ELECTRICIAN

clear process, it’s easy to lose time chasing the wrong cause. In this article, we’ll walk through a practical step-by-step checklist to help you find and fix LED flicker fast. Start with the most likely causes: 1ST CHECK: LOOSE CONNECTIONS Loose terminations are one of the most common causes of flicker. When a connection isn’t tight, the metal-to-metal contact can be poor or intermittent (and can even arc slightly under load). That increases resistance and causes unstable voltage or brief interruptions in supply – something LEDs and drivers show as flicker. If you’re very lucky, a lamp may just need a small twist to seat properly. If not, here’s how to locate the cause…

In this article the experts at ROBUS look at what might be causing LED lights to flicker and how to fix the issue fast.

How to check Isolate and prove dead. Then re-check the whole loop: at the switch (common, switched live, neutrals if present), at each fitting (especially neutrals), and in any junction/maintenance-free connectors. Look and feel for loose conductors, browned insulation, melted terminals, or a “hot” smell. Re-terminate as required, then load-test and confirm the flicker is gone. Common hotspots: First fitting on the run, last fitting (loose loop-out), switch back box, any connector hidden above ceilings, and any borrowed/shared neutral points. 2ND CHECK: DIMMER INCOMPATIBILITY Dimmer incompatibility isn’t just about wattage, it’s about how the dimmer controls the power, and how the LEDs and/or driver reacts to it.

Older leading-edge (triac) dimmers “chop” the mains waveform, which can make some LED drivers buzz, shimmer, pulse, or drop out – especially at lower dim levels. Some LEDs need a trailing-edge dimmer, or a completely different control method (e.g., 0-10 V or DALI), so the LEDs and dimmer must be matched. How to check To begin with, confirm a dimmer is actually in the circuit! Then bypass it temporarily (fit a suitable switch link or test with a working non-dim switch) and re-test for flicker. If the flicker disappears, it strongly indicates that the dimmer is the source of the problem. This means the flicker is not caused by the LED fittings or wiring, but rather by incompatibility between the dimmer and the LED load. The next step is to check if the dimmer is the right type for the LEDs (leadingedge/triac vs trailing-edge), confirm it is rated for LED use, and ensure the connected load falls within the dimmer's minimum and maximum specifications. Where possible, test with a dimmer model listed as compatible by the LED/driver manufacturer. Common hotspots: “Universal”/old triac dimmers, multi-way (2-way/intermediate) dimmer setups, smart dimmers, and dimmers without a neutral (more prone to nuisance behaviour at low loads).

3RD CHECK: MINIMUM LOAD ISSUES Dimmers, drivers, and even smart switches often specify a minimum load to operate correctly. If the connected LED load is too small, the control electronics may “hunt” (constantly searching for a stable operating point and over-correcting), causing shimmer, pulsing, or flashing – especially at low dim levels. Even if the LEDs meet the minimum load at full output, dimming down reduces the power draw. If the load drops below the dimmer’s minimum operating level at low settings, the dimmer can struggle to regulate the LEDs smoothly, resulting in flicker, pulsing, or sudden jumps in brightness near the bottom end. How to check Add up the actual connected load on the dimmer/driver (LED wattages or driver output load), including any fittings on the same switch line. Compare that total to the dimmer/driver’s stated minimum load. If you’re under the minimum, test by temporarily adding load (where appropriate) or by swapping to an LED-rated dimmer/driver designed for low loads. Common hotspots: Only 1-2 LED fittings on a dimmer, very low dim settings, noneutral smart controls, and circuits where extra fittings were added/removed over time (load no longer matches what the dimmer was originally sized for). 4TH CHECK: DRIVER MISMATCH Flicker can come from an LED driver that’s the wrong type or is being pushed outside its operating range. Common issues include using a non-dimmable driver on a dimmed circuit, mixing constant-current and constant-voltage components, or exceeding driver limits due to too many fittings. Alternatively, low-quality drivers can introduce flicker – even on a stable supply – due to poor internal regulation.

How to check Identify the driver type and rating (constant current vs constant voltage, output range, dimmable/non-dimmable) and confirm it matches the fittings on the circuit. Check for overload (too many fittings) or underload (outside the driver’s operating range). If the circuit is dimmed, confirm the driver is dimmable and compatible with that dimming method. Swap in a trusted, correctly rated driver to confirm. Common hotspots: Non-dimmable drivers on dimmer circuits, mixed driver types on the same control, long cable runs causing voltage drop on 12/24 V systems, and incorrect replacement drivers fitted during maintenance. FINAL CHECK: SUPPLY STABILITY If everything checks out, consider the supply. Voltage fluctuations, shared circuits, or interference from other loads can all cause LED flicker – even when the fittings and controls are correct. The best way to avoid flicker call-backs is to start with proven, compatible gear. Stick to trusted manufacturers (like ROBUS), follow the stated dimmer/driver compatibility guidance, and keep the load within spec. Then the only flicker faults you’ll be chasing are the special case Fridayafternoon head-scratchers. BROWSE OR DOWNLOAD THE 2026 ROBUS LIGHTING CATALOGUE AT: WWW.RDR.LINK/EBZ014

PROFESSIONAL ELECTRICIAN CPD Book 91

Dr. Zzeus IN THIS REGULAR COLUMN, DR. TOM BROOKES, MD AT ZZEUS TRAINING AND CHAIRMAN OF THE BSI TECHNICAL COMMITTEE FSH 12/1 INSTALLATION AND SERVICING, ANSWERS YOUR QUESTIONS RELATED TO FIRE SAFETY. IN THIS EDITION HE OFFERS ADVICE ON EXTENDING OR MODIFYING EXISTING FIRE ALARM SYSTEMS. Q: When extending or modifying a fire alarm system, what does BS 5839-1:2025 actually require, and where do engineers get it wrong? The key principle in BS 5839-1:2025 is simple: You are responsible for the work you carry out – and its impact on the system! Extensions and Modifications under BS 5839-1:2025 – Section 7 Clauses 45 & 46

During the lifecycle of a fire detection and fire alarm system, change is inevitable. Buildings are altered, layouts evolve, and system performance is refined in response to operational requirements or false alarms. In these circumstances, engineers are often required to extend or modify an existing system. While these tasks may appear routine, the 2025 edition of BS 5839-1:2025 makes it clear that they carry significant responsibility and must be approached with care. An extension involves adding to the system, such as installing additional detectors, extending circuits, or protecting new areas. A modification involves altering the existing system, for example, by changing detector types, relocating devices, or adjusting cause-and-effect programming. The distinction is important, as the standard applies different expectations to each. A key principle within Clause 45 is that, when extending a system, only the new work is required to comply with the current standard. The existing

92 CPD Book PROFESSIONAL ELECTRICIAN

installation may remain unchanged, even if it doesn’t fully conform. However, this shouldn’t lead to complacency. Where the extent of an extension is significant, particularly if it approaches the scale of the original installation, consideration should be given to upgrading or replacing the system, especially where it falls well short of current recommendations. In practice, one of the most critical risks associated with extensions lies in system compatibility. This is particularly evident in addressable and networked systems, where extending circuits using cable with different electrical characteristics can introduce communication issues. Variations in impedance can result in unreliable data transmission, intermittent faults, and long-term instability. Where the original cable type is no longer available, it may be necessary to replace the entire circuit rather than attempt a partial extension. Responsibility for extension work must rest with a competent person who understands system design principles and is familiar with the requirements of the standard. Following completion, the system should be recommissioned to confirm that the extension hasn’t adversely affected the existing installation. This includes checks on system loading, battery capacity, signal integrity, and cause-and-effect operation. An extensions or modifications certificate should then be issued to formally record the work undertaken. Modifications, addressed in Clause 46, carry an even greater level of

responsibility because they effectively involve an element of redesign. Whether the change is physical or relates to system configuration, the impact on the overall system must be carefully assessed. The standard requires that the user is informed of any proposed modification and that their agreement is obtained before work proceeds. A key challenge with modifications lies in software and configuration changes. Even minor adjustments to cause-and-effect programming can introduce unintended consequences elsewhere in the system. For this reason, testing must extend beyond the immediate area of work. Additional checks are required to confirm that the wider system hasn’t been compromised, including circuit integrity and power supply capacity. Documentation is another critical requirement. Following any modification, all relevant records should be updated, including as-fitted drawings, system configuration, and operation and maintenance manuals. Importantly, modifications must not introduce new non-conformities. Ultimately, both extensions and modifications require a professional approach that considers the system as a whole. Engineers must ensure that their work doesn’t compromise the integrity, reliability, or compliance of the installation.

SECTION SIX

GRID GETAWAY Steve Humphreys, Technical Commercial Manager at NAPIT, explains how battery storage systems can safely operate in island mode. From isolators to earth electrodes and system referencing relays, he outlines the key components that ensure automatic disconnection of supply (ADS) protects essential circuits when the grid goes down.

ith so many battery inverters and all-in-one systems, it can be diﬃcult for designers and installers to select a system that provides the required fault protection against electric shock in island mode. Island mode occurs when the battery storage system operates independently from the main grid supply. When the grid supply is lost, the battery system supplies power to essential consumer loads, eﬀectively creating an “island” of power. This article looks at how fault protection through automatic

disconnection of supply (ADS) can be achieved using three critical components operating in the correct sequence. Island mode isolator An island mode isolator is required to meet the requirements of Section 551 of BS 7671, that deals with low voltage generators and Regulation 21 of the Electricity Safety, Quality and Continuity Regulations (ESQCR). Regulation 21 of the ESQCR states: “Where a person operates a source of energy as a switched alternative to a distributor’s network, they shall ensure that the source of energy cannot operate in parallel with that network and where the source of energy is part of a low voltage consumer’s installation, that installation shall comply with British Standard Requirements.” BS 7671 and Regulation 551.6.1 go into more detail on how to

achieve this by stating: Precautions shall be taken so that the generator cannot operate in parallel with the system for distribution of electricity to the public. Suitable precautions may include one or more of the following:

PROFESSIONAL ELECTRICIAN CPD Book 93

SECTION SIX

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An electrical, mechanical or electromechanical interlock between the operating mechanisms or control circuits of the changeover switching devices A system of locks with a single transferable key A three-position break-before-make changeover switch An automatic changeover switching device with a suitable interlock Other means providing equivalent security of operation

During island mode, the isolator must disconnect all live conductors, including the neutral, to prevent backfeeding into the grid and protect anyone working on the distribution system, such as line workers. Relays alone do not meet the requirements of the ESQCR Regulations 21 and 22, or appropriate British, CENELEC or IEC Standards in BS 7671. The isolator must meet the requirements of BS 7671 and speciﬁcally Table 537.4.

94 CPD Book PROFESSIONAL ELECTRICIAN

The isolator could be integral to the inverter in the form of a contactor that complies with BS EN IEC 60947-4-1 or an external manual switching device complying with BS EN IEC 60947-3, see Fig 1. Consumers earth electrode In island mode the battery storage system will need to be provided with a means of earthing. This is often overlooked in the design of systems that are capable of supplying back-up power in the event of the grid supply being lost. It stands to reason that any essential loads being supplied during island mode still need to have fault protection. BS 7671 tells us that during a loss of grid supply the distributors earth connection cannot be relied upon. This is stated in Regulation 551.4.3.2.1: “Protection by automatic disconnection of supply shall not rely upon the connection to the earthed point of the system for distribution of electricity to the public when the generator is operating as a switched alternative to a TN system. A suitable means of earthing shall be provided” This means that a consumer’s earth electrode shall be provided for TN systems, as shown in Fig 2. The consumers earth electrode shall be connected to the main earthing terminal, and the earthing conductor shall be suitably sized in accordance

“BS 7671 tells us that during a loss of grid supply the distributors earth connection cannot be relied upon. This is stated in Reg 551.4.3.2.1.” with Chapter 54 of BS 7671. In TT systems, the existing consumers earth electrode can be used if its suitability has been conﬁrmed, i.e. stable with a low resistance (not exceeding 200 Ω). System referencing relay The system referencing relay, previously known as the neutral/earth bond relay, is a component part of the system that is integral to island mode operation. In island mode we cannot have two neutral connections to protective earth at the same time. Ultimately this will help prevent circulating neutral currents, unwanted tripping of RCDs and reduce the risks for DNO engineers working on the network. When the system moves into island mode, the system referencing relay closes to create a neutral/earth bond between the neutral of the essential circuits to be supplied by the battery storage system and earth, as shown in Fig 3.

The system referencing relay must: ● Close immediately after the island mode isolator opens for island mode operation ● Open immediately before the island mode isolator closes for connected operation The system referencing relay contact should be rated to be capable of making or breaking the largest sum of the prospective currents from all sources capable of simultaneously operating in parallel. The system referencing relay should be connected between neutral and protective earth as near to the output of the inverter as possible. Bringing it all together Now we have looked at these three parts of the system and explained what they do, we can bring them all together to show how they work in unison. 1. Once the grid supply is lost, the island mode isolator will disconnect all live conductors 2. The system referencing relay closes immediately after the island mode isolator opens (typically within a fraction of a second). This ensures only one neutral is connected to the protective earth 3. The consumers earth electrode has now become our reference point between the neutral of any essential

circuits to true Earth 4. In island mode, a TN-S earthing arrangement has now been created The diagrams in Fig 4 and Fig 5 show the diﬀerences between Connected and Island modes using TN-C-S and TN-S arrangements. For all connected mode supply earthing arrangements, it is recommended to switch to a TN-S earthing arrangement in island mode. Where PME conditions apply in connected mode, these conditions will remain in island mode, because for TN-C-S and TN-S supplies the installation remains connected to the distributor’s means of earthing. However, as stated earlier in Regulation 551.4.3.2.1, the suppliers earth connection cannot be relied upon in island mode, it may be lost or become unreliable, so the system needs a new, dedicated earth to protect against electric shock. Now that we have an earth reference point in island mode, along with suitable protective devices, essential circuits being supplied by the battery storage system will have fault protection by automatic disconnection of supply (ADS). A word of caution: some inverter manufacturers claim the consumer earth electrode and system referencing relay are unnecessary. This type of inverter may use a ‘ﬂoating voltage’ arrangement that is unearthed during island mode operation, similar to an IT system.

“A word of caution: some inverter manufacturers claim the consumer earth electrode and system referencing relay are unnecessary. This type of inverter may use a ‘floating voltage’ arrangement that is unearthed during island mode operation, similar to an IT system.” This type of system is not suitable for domestic battery storage systems and may violate BS 7671, The Electricity at Work Regulations (EAWR) and The Electricity Safety, Quality and Continuity Regulations (ESQCR). Conclusion Essential circuits being supplied during island mode still need to have fault protection. Therefore, designers, installers and inspectors need to consider how fault protection is achieved during island mode operation of battery storage systems. In this article we have shown how fault protection, using ADS, can be achieved in island mode by selecting the correct equipment and component parts and ensuring they operate correctly and safely. FOR MORE INFORMATION ON NAPIT SCHEME REGISTRATION VISIT: WWW.RDR.LINK/EBZ015

SECTION 6 ENDS! SCAN THE QR CODE TO CLAIM YOUR CPD CREDIT FOR THIS SECTION OR VISIT: WWW.RDR.LINK/EBZ016

PROFESSIONAL ELECTRICIAN CPD Book 95

ADVERTISER INDEX Here is a useful summary of all the adverts that appear in this special issue of Professional Electrician.

Aico ........................................................................................................................................................................................................................ page 20 BEX Group ROBUS ............................................................................................................................................................................................ page 26 Carl Kammerling International ...................................................................................................................................................................... page 73 Chauvin Arnoux .................................................................................................................................................................................................. page 85 CHUMP Tools ...................................................................................................................................................................................................... page 43 City Electrical Factors ........................................................................................................................................................................................ page 4 CPD Tracker App ................................................................................................................................................................................................ page 61 C-TEC...................................................................................................................................................................................................................... page 96 ELEX Show ........................................................................................................................................................................................ inside back cover Elite Security Products .............................................................................................................................................................. outside back cover Elucian.................................................................................................................................................................................................................... page 36 Ledvance .............................................................................................................................................................................................................. page 48 Live Electrical Distribution UK ...................................................................................................................................................................... page 62 Luceco Group ...................................................................................................................................................................................................... page 29 NAPIT...................................................................................................................................................................................................................... page 33 NICEIC .................................................................................................................................................................................................................... page 65 Ovia Lighting........................................................................................................................................................................................................ page 52 Power Quality Expert........................................................................................................................................................................................ page 55 Rointe ...................................................................................................................................................................................................................... page 13 Scolmore International.................................................................................................................................................................. inside front cover Thorlux...................................................................................................................................................................................................................... page 5 Unicrimp ................................................................................................................................................................................................................ page 78 WAGO .................................................................................................................................................................................................................... page 40

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