Code Q&A: Rounding Up Rules

March 28, 2019

Is the answer obvious to you? Check and see if you're right.

Q. Does the NEC allow overcurrent protection for conductors to be rounded up to the next larger size?

See the answer below.

A. Absolutely! The next higher standard rating of overcurrent protection device listed in Sec. 240.6 (above the ampacity of the ungrounded conductors being protected) is permitted, provided all of the following conditions are met [Sec. 240.4(B)]:

(1) The conductors aren’t part of a branch circuit supplying more than one receptacle for cord-and-plug-connected loads.

(2) The ampacity of a conductor, after the application of ambient temperature correction [Sec. 310.15(B)(2)(a)], conductor bundling adjustment [Sec. 310.15(B)(3)(a)], or both, doesn’t correspond with the standard rating of a fuse or circuit breaker in Sec. 240.6(A).

(3) The overcurrent protection device rating doesn’t exceed 800A.

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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.