Motors & EquipmentQuestion 86 of 120
For that 34-ampere three-phase squirrel-cage motor, what is the maximum inverse-time circuit breaker permitted for branch-circuit short-circuit and ground-fault protection, using the next standard size allowance?
a.90 amperes
b.85 amperes
c.100 amperes
d.70 amperes
Explanation
An inverse-time breaker is permitted at 250 percent of full-load current: 34 x 2.50 = 85 A, which is not a standard rating, so the next higher standard size of 90 amperes may be used. The 100-ampere answer skips a standard size, and 70 amperes corresponds to the 175 percent dual-element fuse calculation instead.
Law Reference: 2023 NEC Table 430.52(C)(1)Practice all 120 questions free — no signup required.
Related questions on this topic
- A 25-horsepower, 460-volt, three-phase squirrel-cage motor has a table full-load current of 34 amperes. Using 75 degrees C terminations and copper, what is the minimum branch-circuit conductor size?
- That same motor has a nameplate full-load current of 32 amperes and a marked service factor of 1.15. What is the maximum separate overload device rating?
- For the same 34-ampere motor, what is the maximum dual-element time-delay fuse permitted at the standard percentage?
- A 5-horsepower, 230-volt single-phase motor has a table full-load current of 28 amperes. What is the minimum copper branch-circuit conductor at 75 degrees C terminations?
- A 30-horsepower, 460-volt three-phase motor has a table full-load current of 40 amperes. What is the minimum ampere rating of the disconnecting means?
- A feeder supplies a 25-horsepower motor (34 amperes) and a 10-horsepower motor (14 amperes), both 460 volts three phase. What minimum conductor ampacity is required?
Last reviewed: · editorial process
PrepPass Editorial Team · Verified against Journeyman Electrician Licensing Exam (NEC-based) · How we review