For a safety switch installed near a motor with the maximum permitted DETD fuses, when the smallest permitted circuit conductors are used between the switch and the motor, the smallest size EGC permitted is which AWG?

For a safety switch installed near a motor with the maximum permitted DETD fuses, when the smallest permitted circuit conductors are used between the switch and the motor, the smallest size EGC permitted is which AWG?

• A. 10
• B. 14
• C. 12
• D. 8

Answer: (D)

The main idea is that the equipment grounding conductor (EGC) size for a motor circuit is determined by the overcurrent protective device (OCPD) rating, not by the motor current alone. NEC 250.122 requires the EGC to be large enough to carry fault current back to the source quickly enough for the protective device to trip. With the safety switch near the motor and using the maximum permitted fuses, the OCPD rating is at the upper end for that circuit. The smallest conductors between the switch and the motor are chosen to meet ampacity, but the EGC must still meet the table for that OCPD size. For that OCPD rating, the table calls for an 8 AWG copper EGC. So the smallest EGC permitted is 8 AWG. Smaller sizes (10, 12, or 14 AWG) would not provide the required fault-current path for that OCPD rating.

The main idea is that the equipment grounding conductor (EGC) size for a motor circuit is determined by the overcurrent protective device (OCPD) rating, not by the motor current alone. NEC 250.122 requires the EGC to be large enough to carry fault current back to the source quickly enough for the protective device to trip.

With the safety switch near the motor and using the maximum permitted fuses, the OCPD rating is at the upper end for that circuit. The smallest conductors between the switch and the motor are chosen to meet ampacity, but the EGC must still meet the table for that OCPD size. For that OCPD rating, the table calls for an 8 AWG copper EGC. So the smallest EGC permitted is 8 AWG. Smaller sizes (10, 12, or 14 AWG) would not provide the required fault-current path for that OCPD rating.