Code Q&A: Branch Circuit Overcurrent Protection

NEC guidelines for branch-circuit overcurrent protection

Sept. 22, 2016

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Q. What is the minimum size requirement for branch circuit overcurrent protection?

Find the Answer

A. Branch-circuit overcurrent devices must have a rating of not less than 125% of the continuous loads, plus 100% of the noncontinuous loads [210.20(A)]. Note: See Sec. 210.19(A)(1) for branch-circuit conductor sizing requirements.

Exception: If the assembly and the overcurrent devices are both listed for operation at 100% of their rating, the branch-circuit overcurrent device can be sized at 100% of the continuous load.

It’s important to note that equipment suitable for 100% continuous loading is rarely available in ratings under 400A.

As noted in Sec. 210.20(B), branch-circuit conductors must be protected against overcurrent in accordance with 240.4. In addition, as noted in Sec. 210.20(C), branch-circuit equipment must be protected in accordance with 240.3.

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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.