What is the minimum size equipment-grounding conductor for a receptacle rated at 50 amperes protected by an overcurrent device rated at 40 amperes?

The minimum size equipment-grounding conductor for a circuit needs to be determined based on the rating of the overcurrent protection device and the specific requirements set forth in the National Electrical Code (NEC). For an overcurrent device rated at 40 amperes, the NEC typically requires that the grounding conductor be sized appropriately to ensure safety during fault conditions.

In this case, the correct choice is 10 AWG copper, as it meets the NEC requirements for an equipment-grounding conductor when associated with a receptacle rated for 50 amperes. According to NEC Table 250.122, for a circuit protected by a 40 amp overcurrent device, an equipment-grounding conductor of 10 AWG copper is sufficient. This conductor must be capable of safely carrying any fault current back to the source to facilitate the operation of overcurrent devices in the event of a fault.

While other sizes of grounding conductors might be used for different amperage ratings or types of circuits, they do not comply with the specific requirements for this 40 amp configuration. For example, 12 AWG and 14 AWG copper conductors are under-rated for this application, and although 8 AWG is larger, it exceeds the minimum requirement specified for the 40