Oklahoma Electrical Practice Exam

What is the smallest sized copper grounding wire for a subpanel with a 500a OCPD as its disconnecting means?

1. #4 AWG

2. #2 AWG

3. #3 AWG

4. #1 AWG

The correct answer is: #2 AWG

To determine the appropriate size of copper grounding wire for a subpanel with a 500-ampere overcurrent protective device (OCPD), the National Electrical Code (NEC) provides guidance on grounding conductor sizing. For a subpanel with an OCPD rated at 500 amperes, the minimum grounding electrode conductor size for copper is generally specified based on the size of the OCPD. In this case, for a 500-amp service, the NEC indicates that the grounding conductor should be at least #2 AWG copper. This sizing is intended to ensure safety in the event of a fault or electrical disturbance, providing a sufficient path for fault current to safely ground and prevent hazards such as equipment damage or electric shock. Selecting an appropriately sized grounding conductor is crucial for the safe operation of electrical systems, as it helps ensure effective grounding, aids in the clearing of faults, and maintains stability within the electrical system. Thus, the choice of a #2 AWG copper wire is the correct and compliant solution for a subpanel supplied by a 500-amp OCPD.