Code Q&A: Supplementary Overcurrent Protection Rules

Jan. 10, 2019

Here's a refresher on where you can and can't use supplemental overcurrent protection devices.

Q. What is the NEC rule for the use of supplementary overcurrent protection?

See the answer below.

This answer is based on the 2017 NEC.

A. Supplementary overcurrent protection devices aren’t permitted to be used as the required branch-circuit overcurrent protection device [Sec. 240.10]. A supplementary overcurrent protection device isn’t required to be readily accessible.

Article 100 defines a “Supplementary Overcurrent Protection Device” as a device intended to provide limited overcurrent protection for specific applications and utilization equipment. This limited overcurrent protection is in addition to the overcurrent protection provided in the required branch circuit by the branch-circuit overcurrent protection device. See Sec. 240.24(A)(2) for requirements regarding overcurrent protection devices that are not intended for supplemental use.

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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.