What type of wiring system includes wire sizes No. 40 to No. 4/0?

The American Wire Gauge (AWG) system is widely used for denoting wire sizes in electrical applications, which includes sizes ranging from No. 40 to No. 4/0. This system assigns a specific gauge number to each size of wire, indicating its diameter and current-carrying capacity. The AWG scale is inverse - as the gauge number decreases, the wire size increases. For instance, a lower gauge number corresponds to a thicker wire, which is capable of carrying more current.

This system is fundamental in various electrical and electronic applications, ensuring compatibility and safety in wiring practices. Furthermore, the AWG sizing is crucial when determining the appropriate wire for installations to prevent overheating and ensure efficient electrical flow.

While other options like micro-critical manner (MCM) and thousands of circular mils (kcmil) are also associated with wire sizing, they pertain to different applications or standards. The National Electrical Code (NEC) is a set of regulations governing electrical installations but does not specifically define wire sizes. Thus, the correct identification of wire sizes No. 40 to No. 4/0 rests with the American Wire Gauge system.