Which of the following is NOT an acceptable grounding electrode for a service grounding electrode system?

• A. an underground metal gas pipe with at least 10 ft direct contact with earth
• B. a single electrode driven into the earth
• C. a concrete-encased electrode (Ufer) installed properly
• D. a metal water pipe in contact with earth

Answer: (A)

The main idea is understanding which items can legitimately serve as a grounding electrode for the service grounding system. A grounding electrode provides a reliable, low-impedance path to the earth and must be a permanent part of the structure that remains in contact with earth. A driven electrode into the ground is a classic, robust option that establishes a direct earth connection. A concrete-encased electrode (Ufer) is also acceptable when installed correctly, because it is effectively bonded into the concrete mass that surrounds the rebar, creating a solid earth path. A metal water pipe that is in contact with earth is another common and acceptable grounding electrode, provided there are no insulating gaps between the pipe and the earth.

Underground metal gas piping, however, is not considered an acceptable grounding electrode. Gas piping is part of the fuel gas system and is not designed or guaranteed to provide a stable, low-impedance electrical ground. It can be damaged, corrode, or be interrupted, and obtaining a reliable earth connection through it is not permitted for the service grounding system. Thus, it cannot be used as a grounding electrode, making it the correct answer.