COLUMN
ASK THE EXPERT: RCDS
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Eclipse
Paul Collins, technical and training manager from Hager, summarises some of the most frequently asked questions Hager has received in relation to RCDs – an important section that has been completely revised as part of the 18th Edition – as well as common queries concerning RCCBs and switches.
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Pouch
What has changed regarding RCDs? The new regulations covering RCD technology selection has set out a requirement for specifiers to select the appropriate RCD from the range of four types available. RCDs can prevent fatal electric shocks and is a generic term that covers a range of products, including RCCB, RCBO, SRCD, FCURCD, CBR and MRCD. RCDs offer a level of personal protection that ordinary fuses and circuitbreakers cannot provide.
What type of RCD should I use? RCD use has been in existence for a long time and the new regulations have clarified their selection and specification in order to further enhance safety standards. Electrical contractors need to carefully consider the type of RCD required depending on the type of equipment which may be connected in the installation.
• Type AC RCD Type AC RCD is able to detect and respond to AC sinusoidal residual current only. • Type A RCD A type A RCD is able to detect alternating sinusoidal residual current and residual pulsating direct current suddenly applied or smoothly increasing. • Type F RCD A type F RCD is able to detect and respond to high frequency residual current, as well as pulsating DC residual current.
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• Type B RCD A type B RCD is able to detect and respond to all types of residual current, including smooth DC residual current
Halo Wafer
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What is the change to overload protection of RCCBs and switches? Diversity can no longer be used to assume overload protection of RCCBs and switches. The simplest way of ensuring that a consumer unit conforms is to make sure that all RCCBs and switches are rated at or above the rating of the upstream protection, i.e. if the cut out fuse is rated at 100A, all switches and RCCBs within the board should also be 100A. Alternatively, contractors can ensure that the sum of the current rating of the downstream loads is less than or equal to the rating of the RCCBs or switches.
Stratos
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Hager, hager.co.uk/18thEdition; facebook.com/HagerRegsLive
www.emelux.co.uk November 2018 | 25
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