Construction

Code Q&A

May 30, 2003

When you find yourself stumped by the Code, just e-mail your question to [email protected] or visit www.mikeholt.com. Your question and Mike's answer may be posted in a future Code Q&A column. Q. What is the maximum ground resistance required by the NEC for the grounding electrode system? A. There is no maximum ground resistance specified for the grounding electrode system. However, if a single ground

Mike Holt

When you find yourself stumped by the Code, just e-mail your question to [email protected] or visit www.mikeholt.com. Your question and Mike's answer may be posted in a future Code Q&A column.

Q. What is the maximum ground resistance required by the NEC for the grounding electrode system?

A. There is no maximum ground resistance specified for the grounding electrode system. However, if a single ground rod is used as the required grounding electrode system, and it’s resistance exceeds 25 ohms, then it must be augmented by one additional electrode located no less than 6 ft from the original ground rod (250.56).

Example: If the first ground rod has a ground resistance of 100 ohms, you only need to add one additional ground rod, regardless of the resistance of the two ground rods.

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.