Motors & EquipmentCâu 90 / 120
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?
a.67.5 amperes
b.60 amperes
c.48 amperes
d.56.5 amperes
Giải thích
Feeder conductors for several motors must carry 125 percent of the largest motor full-load current plus the sum of the other full-load currents: (34 x 1.25) + 14 = 42.5 + 14 = 56.5 A. The 48-ampere answer simply adds the two currents, and 67.5 amperes wrongly applies 125 percent to the total of both motors.
Trích dẫn luật: 2023 NEC §430.24Luyện miễn phí toàn bộ 120 câu hỏi — không cần đăng ký.
Câu hỏi liên quan cùng chủ đề
- 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?
- For that same two-motor feeder, if the largest branch-circuit protective device is 90 amperes, what is the maximum feeder overcurrent device rating?
- When sizing motor branch-circuit conductors and short-circuit protection, which current value must be used?
- A continuous-duty motor over 1 horsepower is marked with a temperature rise of 40 degrees C but no service factor. What percentage of nameplate full-load current sets the maximum overload device?
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