How are conductor sizes expressed in the NEC?

Conductor sizes in the National Electrical Code (NEC) are expressed in American Wire Gauge (AWG) for standard conductors and circular mils for larger conductors. The AWG system is a standardized wire gauge system used primarily in the United States, where smaller gauge numbers indicate thicker conductors, while larger gauge numbers indicate thinner conductors. For example, a 12 AWG wire is thicker than a 14 AWG wire.

In addition to AWG, circular mils may be used for larger conductors, especially when dealing with wire sizes beyond the AWG standard. The circular mil is a unit of area used to describe the size of round conductors and is derived from the diameter of the wire. This is especially important in the NEC because the size of the conductor is crucial for determining the ampacity, or current-carrying capacity, and to ensure safety in electrical installations.

The other options (square millimeters, inches, and linear feet) do not align with the commonly accepted practices for expressing electrical conductor sizes in the NEC. Square millimeters might be used in other contexts or regions but is not the standard in the NEC. Inches and linear feet measure length rather than cross-sectional area or gauge, which are the