EC&M Tech Talk Video — Ampacity and the NEC
In this episode of “EC&M Tech Talk,” Randy Barnett, a journeyman electrician, electrical instructor, inspector, author, trainer, and electrical safety expert discusses the ampacity level of conductors. The definition of ampacity appears in Art. 100 of the National Electrical Code (NEC). Using this definition, Randy runs through an example to help explain ampacity.
The three conditions of use identified in Art. 310 are important when it comes to determining ampacity values. First, the location of the wiring method can affect insulation properties. Secondly, the number of conductors in the raceway or buried in the earth affects the heat dissipation from the conductors. And third, ambient temperature affects the resistance of the conductor.
Randy reviews various conductor material types identified in the Code such as copper and aluminum. He also provides an overview of the various insulation options. Insulation types are made primarily from PVC or cross-linked polyethylene (XLPE). The thermoplastic insulations are produced from PVC and are the most common type of building wire. Thermoset insulation is produced from XLPE material. To help make sense of the types of insulation, a coding system is used and printed on the conductor insulation every 24 in.
Finally, Randy walks through an example to show viewers the process used to determine the ampacity of a 12 AWG THHN conductor under different conditions of use. The final answer and the steps to arrive at the answer are provided on screen.
