Selection of Ampacity

Dec. 22, 2014
Section 310.15 outlines the requirements for the ampacities of conductors rated between 0V and 2,000V.

The ampacity of a conductor can be different along the length of the conductor. The higher ampacity can be used beyond the point of transition for a distance of no more than ____ ft, or no more than ____% of the circuit length figured at the higher ampacity, whichever is less.

a) 10, 10
b) 10, 20
c) 15, 15
d) 20, 10

See answer and applicable Code reference

The correct answer is: a) 10, 10

Section 310.15 outlines the requirements for the ampacities of conductors rated between 0V and 2,000V. As noted in 310.15(A)(2), "Where more than one ampacity applies for a given circuit length, the lowest value shall be used." However, an exception notes: "Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 10 ft or 10% of the circuit length figured at the higher ampacity, whichever is less."

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.

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