What is the maximum rod-type grounding electrode diameter for which listing is required?

• A. 1/2 in
• B. 5/8 in
• C. 3/4 in
• D. 1 in

Answer: (B)

The main idea is the size threshold that governs when a grounding electrode rod must be a listed product. In the NEC, rod-type grounding electrodes up to a certain diameter are allowed for use without requiring a listed electrode, while larger diameters must be listed to ensure they meet approved standards. That threshold is 5/8 inch. So rods with a diameter of 5/8 inch or smaller are acceptable without needing a listed electrode, and larger diameters require listing. Hence, the maximum diameter described in this rule is 5/8 inch.