Code Q&A

Q. We do a lot of generators for residences, and only recently have been getting written up on our transfer switches. The inspectors are saying that if I use the transfer switch to transfer the entire house — and I put it between the meter and the service disconnect — then the transfer switch must be 'service rated.' Can you help me understand the rules, please?

Mike Holt

Oct. 8, 2009

Q. We do a lot of generators for residences, and only recently have been getting written up on our transfer switches. The inspectors are saying that if I use the transfer switch to transfer the entire house — and I put it between the meter and the service disconnect — then the transfer switch must be "service rated." Can you help me understand the rules, please?

A. There are a couple of rules that have to be followed that ultimately get you to what your inspector is saying. In general, electrical equipment must not be connected to the supply side of the service disconnect enclosure, which means that transfer equipment can’t be on the supply side of the service disconnect [230.82.]. Therefore, you must make your transfer switch your service disconnect. In order to do that, it must be listed as "suitable for use as service equipment" [230.66].

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.