Chapter Three NEC and HVAC - Article 300 - Wiring Methods

Chapter Three NEC and HVAC - Chapter Three in the NEC covers Wiring Methods which includes how the wiring is supposed to run, the 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 add 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. However, it never hurts to learn a little about a related trade.

Chapter Three NEC and HVAC - NEC – Article 310 and the Wire Sizing Tables – HVAC & NEC Basics

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 with THHN, THHW, and MTW (refers to the outer jacket of the wire) wire as these are the types of conductors used most frequently in the residential and commercial markets for wiring and wiring in HVAC equipment.

That purpose using a specific type of wire in the equipment is for safety reasons. The wire needs to be able to hold up to the conditions, including temperature, inside the equipment.

Not so much the ambient temperature, that is a factor, but more importantly, the amperage going through the wire.

Each of these wire types has 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 amperage’s 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 very important to note the differences between copper and aluminum.

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 very important to note the differences between copper and aluminum.

Chapter Three NEC and HVAC - Article 312 NEC and HVAC

OSHA and HVAC Safety Article 312 of the NEC covers cabinets, cutout boxes, and meter socket enclosures. Most HVAC equipment 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 are not directly integrated or come directly integrated to the HVAC equipment.

Usually in that 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.

Chapter Three NEC and HVAC

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. This is basic common sense however one can find many panels with conduit/wiring penetrations on the top, especially 3R cabinets.

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.

Chapter Four Coming Soon!!!!

The NEC and HVAC Chapter One

The NEC and HVAC Chapter Two

High Performance HVAC

Chapter Three NEC and HVAC – Article 300 – Wiring Methods

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