What Is the Wire Size Per Amp According to NEC Code?

The maximum wire size per amp according to NEC code varies according to the material of the conductor or wire, its temperature rating and the number of current-carrying wires in a cable. The National Electric Code contains wire amperage capacities, or ampacities, for cables containing up to three current-carrying wires.

The code shows different ampacities for copper and aluminum conductors with temperature ratings that range from 60 to 90 degrees Celsius. There are separate tables containing factors to apply to the ampacities shown for ambient temperatures other than 30 degrees Celsius, raceways or cables containing arrays of more than three wires, and single or multi­-conductor cables that are stacked or bundled in lengths exceeding 24 inches.