Selection of Ampacity

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."

 

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