Code Q&A

Aug. 18, 2011

Q. What are the disconnecting requirements for a transformer?

A. A disconnect is required to disconnect all transformer ungrounded primary conductors. The disconnect must be located within sight of the transformer, unless the location of the disconnect is field-marked on the transformer and the disconnect is lockable [450.14], as shown in the Figure. This new Code requirement applies to transformers of any voltage, except Class 2 or Class 3 transformers.

Note: Within sight means that it's visible and not more than 50 ft from one to the other [Art. 100].

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.