The smallest branch circuit conductors that can be installed between the 1-pole circuit breaker in a 120/240-volt, 3Ø, 4-wire panelboard and the motor are which AWG? Terminations are rated at 75°C.

• A. 12
• B. 4
• C. 6
• D. 10

Answer: (B)

The thing being tested is how to size motor branch-circuit conductors based on the motor’s current and the termination temperature rating. For a motor circuit, you don’t just pick a conductor from the breaker size; you size the conductors to carry the motor’s full-load current (and any applicable multiplier) using the ampacity corresponding to the termination rating. Since the terminations are rated at 75°C, you use the 75°C ampacity for each conductor size.

In this scenario, the motor’s required current is large enough that only a conductor of 4 AWG copper has enough ampacity to carry it safely at 75°C terminations. The smaller gauges listed (12, 10, 6) do not provide sufficient ampacity for the motor’s load, given the protection and termination rating. Therefore, 4 AWG is the smallest conductor that meets the motor’s current requirement without overheating.