What size equipment grounding conductor is required for a building with a 400-ampere feeder made up of four 600 kcmil copper conductors?

The correct size of the equipment grounding conductor for a building with a 400-ampere feeder made up of multiple conductors is determined based on the requirements outlined in the National Electrical Code (NEC). For a feeder that has a specific ampacity, the NEC provides guidelines for calculating the appropriate size of the grounding conductor to ensure safety and functionality.

In this case, the feeder carrying 400 amperes indicates a requirement for a grounding conductor that can adequately support fault currents without overheating or causing a failure. According to NEC requirements, when calculating the grounding conductor size for conductors of a given ampacity like 400 amperes, 1/0 AWG copper becomes the appropriate choice when following the guidelines that suggest it should be at least based on a certain percentage of the feeder size and taking into account that the material of the wire is copper.

The options that fall short, such as 6 AWG, 3/0 AWG, and 1 AWG, either do not meet the minimum required size standards set forth for equipment grounding conductors or exceed the safe and typical practices indicated by the NEC. Therefore, 1/0 AWG copper is the correct answer, as it aligns with the specified standards for conductivity and safety for