Which two sizes are used to express conductor sizes in the NEC?

The correct answer highlights that conductor sizes in the National Electrical Code (NEC) are typically expressed using the American Wire Gauge (AWG) system and circular mils.

AWG is a standardized wire gauge system used primarily in North America to determine the diameter and current-carrying capacity of electrical conductors. Lower AWG numbers indicate thicker wires, which can carry more current.

Circular mils, on the other hand, is a unit of measurement used to express the cross-sectional area of a wire. It plays an important role in calculating an electrical conductor's ability to carry current without overheating. Specifically, one circular mil is defined as the area of a circle with a diameter of one mil (one-thousandth of an inch).

Using both AWG and circular mils allows for precise calculations in electrical installations, ensuring safety and efficiency in electrical systems as mandated by the NEC. This combination effectively conveys both the physical dimensions and the electrical properties of the conductors, enabling proper selection for various applications.