What is the minimum diameter of a ground rod?

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

Answer: (B)

Grounding effectiveness depends on the electrode’s ability to transfer fault current into the earth, and the contact area between the rod and soil plays a big role in that. The diameter of the ground rod contributes to both the surface area available for grounding and the rod’s mechanical durability in soil over time. Standards set a minimum diameter to ensure a reliable, long-lasting path to earth; a rod with a diameter of five-eighths of an inch provides enough surface area and strength, whereas a smaller diameter would have less contact area and be more susceptible to corrosion or damage. Larger diameters meet the requirement but are not the minimum, so the smallest acceptable size is five-eighths of an inch.