If a 3-pole, 300-A breaker feeds a motor and 3 AWG conductors are run to the motor, the smallest EGC gauge is which?

If a 3-pole, 300-A breaker feeds a motor and 3 AWG conductors are run to the motor, the smallest EGC gauge is which?

• A. 4
• B. 6
• C. 2
• D. 3

Answer: (A)

Equipment grounding conductor size is set by NEC 250.122 based on the overcurrent device protecting the circuit. The idea is to have a grounding path that can carry fault current long enough for the protective device to trip. For a 300-amp overcurrent device, the minimum copper EGC size per the table is 4 AWG. That makes 4 AWG the smallest conductor that still meets the requirement, even though the motor’s phase conductors are 3 AWG (which are larger). A smaller size like 6 AWG would be undersized, while larger sizes like 2 or 3 AWG are simply bigger than necessary.

Equipment grounding conductor size is set by NEC 250.122 based on the overcurrent device protecting the circuit. The idea is to have a grounding path that can carry fault current long enough for the protective device to trip.

For a 300-amp overcurrent device, the minimum copper EGC size per the table is 4 AWG. That makes 4 AWG the smallest conductor that still meets the requirement, even though the motor’s phase conductors are 3 AWG (which are larger). A smaller size like 6 AWG would be undersized, while larger sizes like 2 or 3 AWG are simply bigger than necessary.