The nec & hvac the basics

The NEC and HVAC: The Basics The National Electrical Code and Heating, Ventilation, and Air Conditioning have some shared roles for both electricians and HVAC Installers and technicians. There are some specific categories in the NEC that are applied to HVAC and making calculations for circuits and wire sizing for HVAC appliances. Aside from the specific categories and chapters in the NEC are directly applicable to HVAC and HVAC appliances it is important that every technician have a basic understanding of the NEC in all aspects especially the categories and chapters that are specifically applicable to HVAC and HVAC appliances.

Admittedly the NEC can cause sleep and/or great frustration at times. Do not operate heavy machinery and make sure you take a deep breath if you become frustrated from reading the National Electrical Code. Seriously, the NEC is a serious book and i9mportant to understand especially for those responsible for sizing wire, disconnect boxes, and other related electrical devices for HVAC. In the commercial world in new construction an engineer would determine the correct wire sizes and disconnect boxes necessary for all the equipment. Sometimes but not always in a the commercial retrofit market an engineer will also determine the correct size of all electrical devices necessary to replace or add HVAC equipment. Whether an engineer of record made the determination for sizing circuits and electrical devices it is always a good thing for the technician to know the correct sizes as the engineer of record determined.

From my personal experience before I became a Master Electrician whenever we needed a new circuit ran we called an electrician or an electrical contractor to do everything including the calculations for the circuit. Throughout the site I tell everyone whenever they are in doubt call a professional so this article or series of articles in no way is intended to replace any professional and competent level of service. This article is simply intended to help technicians sharpen their skills and understand another related trade that parallels the HVAC trade. Something I wish I would have had when I was cutting my teeth.

The National Electrical Code (NEC) and HVAC: The Basics

NEC Chapter One Chapter One of the NEC covers why the code exists and what it covers and what it does not cover. including requirements for installations. Definitions are also included including acronyms e.g. AHJ or Authority Having Jurisdiction.

Basically a lot of definitions which anyone with a technical background can familiarize themselves to improve their technical vocabulary.

Can you confidently define the following electrical words or terms as defined by the NEC? ¡ Bonding Jumper ¡ Feeder

· Disconnecting Means · Grounded Conductor · Grounding Conductor · Overload · Qualified Person · Utilization Equipment These definitions and others are included in Chapter One of the NEC and is considered to be comprehensive enough for one to gain a basic understanding of the electrical trade and to understand the electrical code.

Article 110 in Chapter One of the NEC covers requirements for electrical installations. Of note or pertaining to HVAC is limited in this chapter. There are similarities in the NEC that can be compared to basic common sense as far as installation of equipment is concerned for accessibility and guarding the equipment.

The National Electrical Code (NEC) and HVAC: The Basics The NEC and HVAC Chapter Two Chapter Two of the National Electrical Code (NEC) covers Wiring and Protection and starts at Branch Circuits, Feeder circuits, GFCI requirements and protection,. An HVAC installer may want to pay attention to branch circuit requirements. Article 220 in Chapter two of the NEC includes calculations for branch and feeder circuits including service calculations. (Table 220.3) · Specific branch circuit requirements for HVAC can also be found in Chapter 4 Article 440 - Air Conditioning and Refrigerating Equipment Branch Circuit Conductor Sizing · Article 424 - Fixed Electric Space Heating Equipment Branch Sizing · An entire chapter on motors including feeder circuits for motors Chapter Two of the NEC also covers basic lighting which by code is done by Volt-Amperes per square foot. (Table 220.12) In Chapter Two of the NEC an HVAC Technician can pay particular attention to anything in chapter two pertaining to motor loads and appliances. Before you hook up that condenser or air handler can you find the proper rating reference in the NEC for circuit size for the ampacity of the equipment you are installing?

220.82 (C) Covers heating and air conditioning loads for feeder and service load calculations.

220.83 (B) covers additional air conditioning equipment or electric space heating equipment and load calculation requirements for HVAC equipment described.

225.30 - 225.39 makes a reference to disconnects which is applicable to HVAC equipment and HVAC equipment disconnects.

Article 230 of the NEC covers services or service entrances and not applicable to HVAC applications or HVAC equipment.

Article 240 of the NEC covers overcurrent protection and is applicable to HVAC applications and HVAC equipment. Table 240.3 (NEC 2005) references the following that are applicable to HVAC and overcurrent protection. · Air Conditioning and Refrigerating Equipment - Article 440 · Appliances (possible HVAC) - Article 422 · Fixed electric heating equipment for pipelines and vessels (Specialty HVAC) - Article 427

· Induction and Dielectric Heating Equipment (Specialty HVAC) - Article 665 · Motors, Motor Circuits, and Controllers (Specialty HVAC) - Article 430 All references to specialty HVAC are for HVAC specialty fields are defined as not normally practiced in typical HVAC market ( e.g. residential and light commercial market).

Table 240.4(G) makes specific references to HVAC and Specific Conductor Applications required in the NEC and all references to HVAC in this table are as follows: · Air Conditioning and Refrigerating Equipment - Article 440, Parts III and VI · Motor Operated Appliance Circuit Conductors - Article 422, Part II · Motor and Motor Control Circuit Conductors - Article 430 Parts III, IV, V, VI, and VII Article 240.5 makes a reference to the protection of cords, flexible cables, and fixture wires which are applicable to HVAC appliances that use flexible cords or flexible cables and makes a reference to Tables 400.5(A) and 400.5(B) and relates to the ampacity of the equipment served by the flexible cord or cable. Extension cords are also mentioned in this Article.

240.40 makes a reference for a disconnecting means for fuses in circuits over 150 volts which can be applicable to HVAC equipment since a lot of HVAC equipment is over 150 volts.

Article 240.50 makes a general reference to fuses and the allowable use of fuses. Read that article to see if this applicable to your specific HVAC application.

Chapter Two NEC and HVAC - Article 250 - Grounding and Bonding Grounding and Bonding is applicable to HVAC and HVAC equipment and is very important to any electrical circuit in most residential and commercial HVAC installation. What happens if there is a dead short in a compressor and the homeowner touches the condenser if no ground exists? Current will pass through the homeowner and to the ground where he or she is standing.

Electricity takes the path of least resistance and the homeowner made the circuit from the short in the compressor to ground. The subject of grounding and bonding is very important to understand so I recommend you consult a professional electrician if there are any questions about the circuit(s) being used are properly grounded and/or bonded. This includes the circuit wire size is appropriate and/or the path to ground is effective.

Chapter Two NEC and HVAC - Article 280 - Surge Arresters This is applicable to commercial applications and government retrofit and new construction jobs.

Surge arresters may be something to consider for residential and commercial applications especially for solid-state equipment that utilizes electronics and is highly susceptible to lighting strikes or other natural or unnatural surges. Whether solid state electronics are used or not is good to protect all equipment including HVAC equipment from surges. ​The

NEC and HVAC Chapter Three Chapter Three NEC and HVAC - Article 300 - Wiring Methods Chapter Three in the NEC covers Wiring Methods which includes how wiring is supposed to ran, conduit for wiring, outlets, junctions, and switch points, and a host of other topics about the proper way to run wiring. HVAC Technicians will be familiar with piping support as is required in the Mechanical Code and electricians must follow some of the same rules when running conduit and adding support for the conduit. Protecting the wiring and using the proper wiring methods is the gist of Article 300 and while no mention of HVAC is used in Article 300 it is important for electricians to understand and not so much an HVAC technician unless that HVAC tech aspires

to be an Electrician.

Article 310 in the NEC (2005) is a good Article for HVAC technicians to understand as it deals with conductors, conductor insulation and temperature ratings, the proper wire to use for the voltage and more importantly the proper wire size to use for the amperage. Most HVAC technicians work a lot with THHN, THHW, and MTW wire as these are the types of conductors used most frequently in the residential and commercial markets for wiring and wiring in HVAC equipment. Each of these wire types have their very own operating temperature rating which includes the amount of amperage the wire can handle in the operating environment where it is installed. The Tables of 310.16, 310.17, 310.18. and 310.19 are Tables all HVAC technicians need to be familiar with especially those technicians replacing wiring in and around HVAC equipment whether it be for service and repair, retrofit projects, or new installations these Tables are super important for an HVAC Technician to understand so they use the proper wire and wire size for the amount of amperages the wire will utilize.

Correction factors are noted at the bottom of the Tables so one can make an adjustment to the wire size if the wire will be used in a high ambient environment. Additionally it is important to note the differences between copper and aluminum.

Article 312 in the NEC covers cabinets, cutout boxes, and meter socket enclosures. Most HVAC equipments comes complete with its own panels and cabinets so it is easy to say this Article will not be applicable to HVAC technicians unless the HVAC technician is installing controls like direct digital controls or other types of controls that not directly integrated or come directly integrated to the HVAC equipment. Usually in the case an engineer will specify the type of cabinet or panel to be used in any particular circumstance for example a panel or enclosure located outdoors will require a NEMA rated 3R cabinet or panel to prevent water or dampness from entering the cabinet. The understanding for the HVAC technician comes in handy in this situation because the HVAC technician should understand this and know that no cabinet or panel penetrations for wiring should come into the cabinet or panel from the top or the sides. All attempts to run any wiring to this panel should be made from the bottom of the cabinet or panel to prevent moisture from penetrating the cabinet or panel.

The balance of Chapter 3 in the NEC covers a variety of wire types, cable, conduits, junction box wiring, and other important topics that a good electrician knows and not many HVAC technicians are familiar with. It doesn't hurt to learn other related trades especially the electrical trade if you are an aspiring HVAC technician who wants to be successful.

A good overview of Chapter 3 in the National Electrical Code for an HVAC Technician would be to review the Wire size tables mentioned above and to understand proper wiring methods.

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