The National Electric Code wire ampacity table is used as a guideline for deciding the proper wire type and gauge to safely use for specific current loads in electrical circuits. The code is maintained by the U.S. Fire Protection Association and provides information on safe electrical wiring.
To accurately use the ampacity chart, the electrician must calculate an accurate figure of the total electrical load. She also needs to know the ambient temperature of the locations, access panels and wiring troughs. With this information, an electrician can decide what type of conductor – either copper, aluminum or copper-clad – and what American Wire Gauge thickness is safe to use. A cross-reference chart shows specific common brands of wire and how the environment impacts the load-effectiveness of each brand.
The NEC code is just a guideline. Some states and municipalities use it in their building codes. However, many states and municipalities have their own building codes which may supersede NEC codes. Contractors need to always check with the local building authority for the correct wire amperage guideline to follow in a specific area. A printed version of the NEC code book can be purchased and many online bookstores and electrical supply companies, including Amazon.com. BarnesAndNoble.com and Grainger.com.