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Code Q&A: Auxiliary Electrodes

April 6, 2017

Auxiliary grounding electrode rules

Q. What does the NEC mean by an auxiliary grounding electrode?

Find the Answer

A. Auxiliary electrodes are permitted, but they have no Code requirements since they serve no purpose related to electrical safety. (Figure)

If an auxiliary electrode is installed, it’s not required to be bonded to the building grounding electrode system or comply with the 25-ohm requirement in Sec. 250.53(A)(2), Exception. In addition, the grounding electrode connected to it doesn’t have to be sized per Sec. 250.66.

Caution: An auxiliary electrode typically serves no useful purpose within the scope of the NEC, and in some cases it may actually cause equipment failures by providing a path for lightning to travel through electronic equipment.

Danger: Because the contact resistance of an electrode to the earth is so great, very little fault current returns to the power supply if the earth is the only fault current return path. The result is the circuit overcurrent protection device won’t open and clear the ground fault, and all metal parts associated with the electrical installation, metal piping, and structural building steel will become and remain energized.

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These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visitwww.mikeholt.com/code

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.