What is the smallest permitted GEC to the ground rod from a 400 amp main breaker panel not subject to physical abuse?

The smallest permitted grounding electrode conductor (GEC) for a ground rod connected to a 400 amp main breaker panel, which is not subject to physical abuse, is a size 6 AWG copper wire. This requirement is based on the National Electrical Code (NEC) guidelines that specify the minimum size of the grounding electrode conductor depending on the service rating of the electrical system and the material of the ground rod.

In this case, for a service of 400 amps, the NEC outlines specific sizing for grounding conductors based on the amperage of the service. Since the panel is not subject to physical abuse, the guidelines allow for smaller gauge wires. Using a 6 AWG copper conductor meets the necessary requirements for effective grounding without risking damage from external factors. Larger sizes like 1/0 and others would be excessive for this scenario based on NEC requirements, as they are typically reserved for more demanding grounding needs or areas where damage is a concern.