Question: Does the NEC specify the maximum resistance of a ground rod?
See answer below.
Answer: Yes and no
Explanation: Section 250.53(A)(2) requires that a single ground rod be supplemented by another electrode. An exception allows a single rod if the resistance of this rod is 25 ohms or less. Many installers interpret this wording to mean they’re required to get a reading of 25 ohms or less on the ground rod. However, there is no NEC requirement for a specific resistance of the grounding electrode system. If you have more than one electrode the 25 ohms reading does not apply. In fact, you do not even need to test the resistance of the system. Note: Many specifications on a project do have resistance requirements for grounding electrodes that must be met.
John Lupacchino is a senior design engineer with Gaylor Electric, Inc., in Noblesville, Ind. and serves as an alternate on NEC Code-Making Panel No. 3. He is currently licensed in more than 80 jurisdictions. He can be reached at [email protected].
About the Author
John Lupacchino
Senior Design Engineer
John began his career in electrical construction as an apprentice and worked his way through the trade. He is currently licensed in more than 80 jurisdictions. With more than 35 years of experience, he now plays a vital role in Gaylor Electric’s Engineering Department, where he serves as a senior design engineer. With a focus on design engineering, quality assurance, and code compliance, he has earned the highest level of respect from industry professionals alike. John currently serves as an alternate on NFPA 70 Code Making Panel No. 3. In addition, he enjoys sharing his electrical knowledge through education. As an Associated Builders and Contractors instructor, he continues to help grow a new generation of high-performing construction leaders.
