Equipment & SystemsQuestion 245 of 521
For a 20 HP, 460 V, three-phase motor (FLC 27 A), what is the maximum inverse-time circuit breaker rating for branch-circuit short-circuit and ground-fault protection, using the 250% value of Table 430.52?
a.67.5 A
b.47.25 A
c.81 A
d.54 A
Explanation
Table 430.52 allows an inverse-time breaker at 250% of FLC: 27 x 2.50 = 67.5 A (then the next-standard-size rule of 430.52(C)(1) Ex. may apply). 47.25 A is 175% (dual-element fuse), 81 A is 300% (nontime-delay fuse), and 54 A is 200%.
Law Reference: 2023 NEC §430.52Practice all 521 questions free — no signup required.
Related questions on this topic
- Per NEC Table 430.248, what is the full-load current of a 5 HP, single-phase, 230-volt motor?
- A single continuous-duty 25 HP, 460 V, three-phase motor has an FLC of 34 A (Table 430.250). What minimum conductor ampacity is required for its branch circuit?
- A motor's nameplate shows a full-load current of 40 A and a service factor of 1.15. Under NEC 430.32(A)(1), what is the maximum overload device rating at 125% of nameplate FLA?
- Using the same 20 HP, 460 V motor (FLC 27 A), what is the maximum dual-element (time-delay) fuse permitted by Table 430.52 for branch-circuit short-circuit and ground-fault protection?
- A 5 HP, 230 V, three-phase motor has an FLC of 15.2 A. What is the maximum nontime-delay fuse permitted by Table 430.52 for branch-circuit protection?
- For the same 5 HP, 230 V motor (FLC 15.2 A), what is the maximum instantaneous-trip circuit breaker setting permitted by Table 430.52?
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