Home > National Electrical Code > Code Q&A

Code Q&A

May 30, 2003 12:00 PM, By Mike Holt

When you find yourself stumped by the Code, just e-mail your question to mike@mikeholt.com 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.