Code Q&A

June 13, 2007

When a lighting and appliance panelboard is fed from the secondary of a 3-phase transformer, is the panelboard required to have a main breaker installed in it?

Mike Holt

Q. When a lighting and appliance panelboard is fed from the secondary of a 3-phase transformer, is the panelboard required to have a main breaker installed in it?

A. No. Lighting and appliance branch-circuit panelboards supplied from a transformer, as permitted in 240.21(C), must have overcurrent protection for the panelboard on the secondary side of the transformer. The required overcurrent protection can be in a separate enclosure ahead of the panelboard, or it can be in the panelboard [408.36(A), 408.36(A) Ex. 1, and 408.36(D)].

Exception: A panelboard supplied by a 2-wire system or a 3-wire, delta/delta-connected, 3-phase system, is considered protected by the primary protection device when installed in accordance with 240.4(F) and 240.21(C)(1).

Note: A lighting and appliance branch-circuit panelboard is one with more than 10% of its overcurrent protection devices protecting “lighting and appliance branch circuits,” which are 30A or less circuits with neutral connections [408.34(A)].

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.