Q. Where in the Code are standard ampere ratings for overcurrent protection devices?
See the answer below.
Underlined text denotes a 2017 NEC change.
A. The standard ratings in amperes for fuses and inverse time breakers are shown in Table 240.6(A). The use of fuses and inverse time circuit breakers with nonstandard ampere ratings are permitted [Sec. 240.6(A)].
Additional standard ampere ratings for fuses include 1, 3, 6, 10, and 601.
Fuses rated less than 15A are sometimes required for the overcurrent protection of fractional horsepower motor circuits [Sec. 430.52], motor control circuits [Sec. 430.72], small transformers [Sec. 450.3(B)], and remote‑control circuit conductors [Sec. 725.43].
The ampere rating of an adjustable circuit breaker is equal to its maximum long‑time pickup current setting [Sec. 240.6(B)].
The ampere rating of adjustable‑trip circuit breakers that have restricted access to the adjusting means is equal to their adjusted long‑time pickup current settings [Sec. 240.6(C)].
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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.