Code Q&A: Panelboard Overcurrent Protection

July 23, 2015

NEC rules on the requirements for overcurrent protection for panelboards?

Q. What are the overcurrent protection requirements for panelboards?

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A. Each panelboard must be provided with overcurrent protection located within, or at any point on the supply side of, the panelboard. The overcurrent device must have a rating not greater than that of the panelboard, and it can be located within or on the supply side of the panelboard [408.36].

Exception No. 1: Individual overcurrent protection isn’t required for panelboards used as service equipment where the service disconnecting means consists of up to six circuit breakers mounted in a single enclosure in accordance with Sec. 230.71.

When a panelboard is supplied from a transformer, as permitted in Sec. 240.21(C), the overcurrent protection for the panelboard must be 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(B)].

Plug-in circuit breakers that are back-fed from field-installed conductors must be secured in place by an additional fastener that requires other than a pull to release the breaker from the panelboard [408.36(C)]. The purpose of the breaker fastener is to prevent the circuit breaker from being accidentally removed from the panelboard while energized, thereby exposing someone to dangerous voltage.

CAUTION: Circuit breakers marked “line” and “load” must be installed in accordance with listing or labeling instructions [110.3(B)]; therefore, these types of devices must not be back-fed.

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.