AC Systems Not Required to be Grounded

Section 250.21 focuses on alternating-current systems of 50V to less than 1,000V that are not required to be grounded.

Sept. 17, 2014

Alternating current systems from 50V to less than 1,000V that aren’t required to be grounded as per 250.20(B) must have _____.

a) ground detectors installed
b) the ground detection sensing equipment connected as close as practicable to where the system receives its supply
c) both (a) and (b)
d) ground fault protection for equipment

See answer and applicable Code reference

The correct answer is: c) both (a) and (b)

System grounding requirements are outlined in Part II of Art. 250. Section 250.21 focuses on alternating-current systems of 50V to less than 1,000V that are not required to be grounded. As outlined in 250.21(A) and (B), ground detectors are required for these systems and they shall be connected as close as practicable to where the system receives its supply.

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.