Code Q&A: Ground Detectors

May 9, 2013

Your most pressing National Electrical Code (NEC) questions answered

Q. What are the requirements regarding ground detection systems and labeling for ungrounded systems?

A. Systems that aren't required to be grounded in accordance with 250.20(B) [250.21(A)(4)] must have ground detectors installed [250.21(B)(1)]. Thisground detection sensing equipment must be connected as close as practicable to where the system receives its supply [250.21(B)(2)]. In addition, ungrounded systems must be legibly marked "Ungrounded System" at the source or first disconnecting means of the system, with sufficient durability to withstand the environment involved [250.21(C)].

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.