A ground ring must be installed with a minimum length of ___ feet.

A ground ring must be installed with a minimum length of ___ feet.

• A. 10 feet
• B. 15 feet
• C. 20 feet
• D. 25 feet

Answer: (C)

Grounding systems rely on a low-impedance path to earth to clear faults. A ground ring serves as a buried electrode that encircles the structure and ties into the service grounding conductor. The rule sets a minimum length of 20 feet for this ring so there is enough conductor in contact with the soil to lower impedance to earth under typical conditions. If the ring were shorter, it wouldn’t provide a reliable earth path and wouldn’t meet the requirements for a ring electrode. Longer rings can be used, but 20 feet is the minimum.

Grounding systems rely on a low-impedance path to earth to clear faults. A ground ring serves as a buried electrode that encircles the structure and ties into the service grounding conductor. The rule sets a minimum length of 20 feet for this ring so there is enough conductor in contact with the soil to lower impedance to earth under typical conditions. If the ring were shorter, it wouldn’t provide a reliable earth path and wouldn’t meet the requirements for a ring electrode. Longer rings can be used, but 20 feet is the minimum.