For a grounded 400-ampere AC system, what is the minimum wire size permitted for the grounding-electrode conductor connected to a rod or pipe electrode?

In a grounded 400-ampere AC system, the size of the grounding-electrode conductor must meet specific requirements to ensure safety and proper operation. According to the National Electrical Code (NEC), the minimum size for a grounding electrode conductor connected to a rod or pipe electrode is determined based on the rating of the service.

For a 400-ampere service, the NEC specifies that the minimum size for the grounding-electrode conductor is No. 6 AWG copper. This size ensures that the conductor can safely carry the fault current that may occur, providing adequate protection against electrical shock and fire hazards. The size is critical because it directly affects the effectiveness of the grounding system in dissipating electricity safely into the ground.

Using a larger or smaller conductor than required can compromise the grounding system's effectiveness, either by being unable to handle the fault current or being unnecessarily massive and more costly. Therefore, No. 6 AWG copper not only meets the NEC requirements but also provides a balance between safety, practicality, and cost.