What is the minimum size aluminum grounding conductor required when the feeder is protected at 400 amperes in a 4,160-volt system?

In determining the minimum size aluminum grounding conductor required for a feeder protected at 400 amperes in a 4,160-volt system, one must refer to the National Electrical Code (NEC) guidelines, particularly focusing on sections concerning grounding conductors.

For an aluminum grounding conductor, the NEC provides specific rules and tables for sizing based on the ampacity of the overcurrent protection device. Generally, the sizing is influenced by factors such as the system voltage and the magnitude of current the conductor must handle safely.

According to the NEC tables, for feeders that are protected at 400 amperes, the minimum size of an aluminum grounding conductor is typically 1 AWG. This is because aluminum conductors require a larger cross-sectional area than copper conductors to carry the same amount of current due to their lower conductivity.

The correct answer is 1 AWG because it meets the requirements set by the NEC for a system protected at 400 amperes, ensuring adequate safety and performance in grounding applications.