Equipment & SystemsQuestion 252 of 521
A feeder supplies two three-phase, 460 V motors: 20 HP (FLC 27 A) and 10 HP (FLC 14 A). Per NEC 430.24, what minimum feeder conductor ampacity is required?
a.41 A
b.51.25 A
c.54 A
d.47.75 A
Explanation
NEC 430.24 requires 125% of the largest motor's FLC plus the sum of the others: (27 x 1.25) + 14 = 33.75 + 14 = 47.75 A. 41 A omits the 125% factor, 51.25 A applies 125% to both, and 54 A doubles the largest.
Law Reference: 2023 NEC §430.24Practice all 521 questions free — no signup required.
Related questions on this topic
- When sizing branch-circuit conductors and short-circuit/ground-fault protection for a standard motor, which current value does the NEC require you to use?
- Which motor current rating is used to select the running overload (overcurrent) protection device?
- A motor nameplate reads 28 A full-load, service factor 1.0, temperature rise not marked. What is the maximum overload rating under NEC 430.32(A)(1)?
- A motor disconnecting means must have an ampere rating at least 115% of the motor FLC. For a 15 HP, 460 V, three-phase motor (FLC 21 A), what is the minimum disconnect ampere rating?
- In a motor installation, what is the primary function of the motor controller?
- A motor control circuit tapped from the load side of the motor branch-circuit protection is generally protected against overcurrent according to which NEC provision?
Last reviewed: · editorial process
PrepPass Editorial Team · Verified against California CSLB C-10 Electrical Trade Examination · How we review