Oklahoma Electrical Practice Exam

What is the smallest size copper grounding wire allowed to run in a building for a 480/277v feeder utilized at 400a?

1. #1 AWG

2. #3 AWG

3. #2 AWG

4. #4 AWG

The correct answer is: #3 AWG

When determining the smallest size copper grounding wire for a 480/277V feeder used at 400A, it is essential to consider the grounding requirements as specified in the National Electrical Code (NEC). For service conductors over 200A, the NEC provides specific minimum sizes for grounding conductors based on the feeder's rating. For a 400A feeder, the NEC Table 250.122 indicates that the minimum size for a copper grounding conductor should be based on the equipment that generates or uses the electricity. In this case, the size must be at least #3 AWG. Size #3 AWG copper grounding wire is sufficient to handle fault currents that may occur in a 400A system, ensuring proper grounding and safety. This size helps to mitigate the risk of electric shock hazards and equipment damage by providing an adequate path for fault current to safely return to the ground. Understanding the requirements for grounding conductors is critical for ensuring compliance with electrical safety standards and practices. Thus, using #3 AWG copper wire is appropriate in this scenario.