What is the minimum size of a copper equipment grounding conductor (EGC) required for equipment connected to a 40A circuit?

The correct answer is based on the National Electrical Code (NEC) guidelines, which specify the minimum size of equipment grounding conductors (EGCs) based on the rating of the overcurrent protection device. For a circuit rated at 40 amperes, the NEC directs that the minimum size for a copper EGC is No. 10 AWG. This size ensures that the grounding path is adequately sized to handle fault currents that may occur, providing a safe and effective grounding system for the connected equipment.

Choosing No. 10 AWG achieves compliance with safety standards and helps prevent overheating, which can lead to safety hazards such as electrical fires. Other sizes, such as No. 8, No. 12, or No. 14, do not meet the NEC requirements for a 40A circuit, either being larger than necessary and thus not minimum or being inadequate in size to provide effective grounding.