You installed a 3-pole, 300-A breaker in a panel and ran 3 AWG circuit conductors to a motor. The smallest EGC you can run with the circuit is which AWG?

You installed a 3-pole, 300-A breaker in a panel and ran 3 AWG circuit conductors to a motor. The smallest EGC you can run with the circuit is which AWG?

• A. 4
• B. 6
• C. 2
• D. 3

Answer: (A)

Sizing an equipment grounding conductor is based on the overcurrent protection device rating. For a circuit protected by a 300 A breaker, the NEC requires the copper equipment grounding conductor to be at least 4 AWG. This ensures the fault current has a safe low-impedance path back to the source long enough to trip the breaker and protect the equipment. The hot conductors being 3 AWG doesn’t change the minimum EGC size; 6 AWG would be undersized, while 2 or 3 AWG would be larger (still acceptable) but not the smallest. So the smallest allowed EGC is 4 AWG.

Sizing an equipment grounding conductor is based on the overcurrent protection device rating. For a circuit protected by a 300 A breaker, the NEC requires the copper equipment grounding conductor to be at least 4 AWG. This ensures the fault current has a safe low-impedance path back to the source long enough to trip the breaker and protect the equipment. The hot conductors being 3 AWG doesn’t change the minimum EGC size; 6 AWG would be undersized, while 2 or 3 AWG would be larger (still acceptable) but not the smallest. So the smallest allowed EGC is 4 AWG.