A ground ring must be at least ___ feet long.

A ground ring must be at least ___ feet long.

• A. 5
• B. 15
• C. 8
• D. 20

Answer: (D)

The concept here is the grounding electrode system and how a ring electrode functions. A ground ring is a length of conductor buried around the perimeter of a structure to create a distributed, low-impedance path to earth for fault currents. The minimum length is set at 20 feet to provide enough surface area and coverage in the soil to keep the impedance low and to ensure the system can reliably reference earth under varying soil moisture and conditions. If the ring were shorter, it wouldn’t offer the required effectiveness, which is why the code specifies a minimum of 20 feet. In practice, this ring is connected to the main grounding electrode conductor to form part of the building’s grounding system.

The concept here is the grounding electrode system and how a ring electrode functions. A ground ring is a length of conductor buried around the perimeter of a structure to create a distributed, low-impedance path to earth for fault currents. The minimum length is set at 20 feet to provide enough surface area and coverage in the soil to keep the impedance low and to ensure the system can reliably reference earth under varying soil moisture and conditions. If the ring were shorter, it wouldn’t offer the required effectiveness, which is why the code specifies a minimum of 20 feet. In practice, this ring is connected to the main grounding electrode conductor to form part of the building’s grounding system.