What is the largest size for a copper grounding electrode conductor connected only to a concrete-encased electrode?

The correct answer is based on the requirements outlined in the National Electrical Code (NEC) for grounding systems. Specifically, when connecting a copper grounding electrode conductor to a concrete-encased electrode, the largest permissible gauge is 4 AWG.

The reasoning behind this sizing relates to the purpose of grounding conductors, which is to ensure sufficient capacity to handle fault currents without causing damage or overheating. A concrete-encased electrode, typically a ground rod or similar installation, is effectively a part of the grounding system and provides a reliable path to ground.

The specific requirement for 4 AWG copper as the largest size is also influenced by practical considerations regarding bonding and grounding. A larger diameter conductor can increase the risk of physical damage or be difficult to work with in the installation process.

Ultimately, this size restriction ensures both safety and efficiency in grounding systems. In contrast, smaller gauges, such as 6 AWG or 12 AWG, do not meet the requirements for this specific application, which mandates the use of 4 AWG for optimal grounding integrity and safety compliance.