What is the largest size required for a copper grounding electrode conductor that is connected only to a rod, pipe, or plate electrode?

The correct answer is based on the National Electrical Code (NEC) requirements regarding grounding electrode conductors. When connecting to a grounding rod, pipe, or plate electrode, the minimum size for a copper grounding electrode conductor is determined by the size of the largest ungrounded (hot) conductor supplying the building or structure.

For systems with a service entrance of 100 amps or less, a 8 AWG copper grounding electrode conductor would typically suffice. However, for larger services, the code specifies that a minimum of 6 AWG copper conductor is required, which applies to most installations. The code does not typically require larger than this unless the conditions of service demand it due to specific circumstances or local amendments to the NEC.

This information clarifies why 6 AWG copper is the largest size required for a grounding conductor connected only to a rod, pipe, or plate electrode, making it the appropriate choice. Options larger than 6 AWG, such as 4 AWG, may be used in different applications but exceeds the required size for this scenario, while smaller gauges, such as 8 AWG and 10 AWG, would not meet the minimum requirements as outlined in the NEC for this specific application.