Equipment & SystemsQuestion 274 of 521
For a continuous-duty three-phase motor rated more than 1 HP without integral overload protection, how many overload units are generally required?
a.One overload unit total
b.One overload unit in each phase (three for a three-phase motor)
c.Two units for any motor
d.None if a breaker is used
Explanation
NEC 430.37 and Table 430.37 require an overload device in each ungrounded conductor - three units for a three-phase motor - so a loss of one phase or unbalanced overload is detected. A single unit is insufficient, and a branch-circuit breaker does not provide running overload protection.
Law Reference: 2023 NEC §430.37Practice all 521 questions free — no signup required.
Related questions on this topic
- Using NEC Table 430.250, what is the full-load current of a 50 HP, 460 V, three-phase motor?
- For the 50 HP, 460 V motor (FLC 65 A), what minimum branch-circuit conductor ampacity is required by NEC 430.22?
- For the 50 HP, 460 V motor (FLC 65 A), what is the maximum inverse-time circuit breaker per the 250% column of Table 430.52?
- A continuous-duty motor has a nameplate FLA of 62 A and a service factor of 1.15. What is the maximum overload device rating at 125% under NEC 430.32(A)(1)?
- If the 125% overload device will not allow a 62 A (SF 1.15) motor to start, NEC 430.32(C) permits increasing the overload trip setting to a maximum of what value?
- Per NEC Table 430.248, what is the full-load current of a 2 HP, single-phase, 230 V motor?
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