Code Q&A

Nov. 27, 2007

A single main breaker is installed, then taps supply individual meters with disconnecting means for individual tenants. Should a main bonding jumper be installed at the single main breaker or at each separate disconnect?

Mike Holt

Q. A single main breaker is installed, then taps supply individual meters with disconnecting means for individual tenants. Should a main bonding jumper be installed at the single main breaker or at each separate disconnect?

A. An un-spliced main bonding jumper complying with 250.28 must be installed between the grounded neutral terminal and the metal parts of the service disconnecting means enclosure in accordance with 250.24(C) [250.24(B)]. Remember that the service equipment is the one to six disconnects connected to the load end of service conductors intended to control and cut off the supply to the building or structure [Art. 100, Service Equipment]. The service you described ends at the load side of the single main breaker. The answer to your question is to install the main bonding jumper at the main breaker, and nowhere else.

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.