Motors Lvl 2 Lesson 7

A 60-horsepower, 3-phase, 208-volt squirrel-cage motor is installed with a motor nameplate full-load current rating of 165 amperes. The minimum ampacity of the branch-circuit conductors is calculated to be 211 amperes. The branch-circuit conductors are required to be not less than 4/0 AWG THWN copper, and they are installed in a two-inch rigid metal conduit. The maximum rating of the motor branch-circuit short-circuit and ground-fault protective device using time-delay fuses has been calculated to be not greater than a 350-ampere time-delay fuse when starting current is a problem. Therefore, this motor with 4/0 AWG THWN copper conductors and a full-load current of 169 amperes can be protected by a 350-ampere time-delay fuse.

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An adjustable, instantaneous trip circuit breaker that is a part of a listed combination motor controller with coordinated protection in each conductor is used for the branch-circuit short circuit and ground-fault protection for a 50-horsepower, 230-volt, 3-phase Design B energy-efficient motor. What is the maximum instantaneous trip circuit breaker rating permitted for this application?

1430 A

A nonadjustable inverse-time circuit breaker is used for the motor branch-circuit short-circuit and ground-fault protection for a 1 1/2-horsepower, 460-volt, 3-phase squirrel-cage motor. What is the maximum rating permitted where an inverse-time circuit breaker is used? (Based on the NEC 2020 and earlier)

15 A

An adjustable, instantaneous trip circuit breaker that is a part of a listed combination motor controller with coordinated protection in each conductor is used for branch-circuit short-circuit and ground-fault protection for a 15-horsepower, 440-volt, 3-phase squirrel-cage motor. Calculate the maximum setting for the instantaneous trip rating of this circuit breaker.

168 A

An inverse-time circuit breaker is used for branch-circuit short-circuit and ground-fault protection for a 30-horsepower, 208-volt, 3-phase squirrel-cage motor. Calculate the maximum rating permitted for the circuit breaker.

225 A

A 40-horse power, 230-volt, 3-phase synchronous motor uses non-time delay fuses for motor branch-circuit short-circuit and ground-fault protection. Calculate the maximum rating for a non-time-delay fuse.

250 A

Time-delay fuses are used for motor branch-circuit short-circuit and ground-fault protection for a 125-horsepower, 460-volt, 3-phase wound-rotor motor. What is the maximum rating permitted where time-delay fuses are used for this application?

250 A

What is the maximum rating of the motor branch-circuit short-circuit and ground-fault protective device for a 7 1/2-horsepower, 208-volt, 3-phase squirrel-cage induction motor using time-delay fuses?

45 A

What is the maximum standard rating for a time-delay fuse used as the motor branch-circuit short-circuit and ground-fault protection for a 230-volt, 3-phase hermetically-sealed compressor motor with a branch-circuit selection current (BCSC) of 38 amperes?

60 A

For torque motors, the rated current shall be ? current, and this nameplate current shall be used to determine the ampacity of the branch-circuit conductors covered in 430.22 and 430.24, the ampere rating of the motor overload protection, and the ampere rating of motor branch-circuit short-circuit and ground-fault protection in accordance with 430.52(B).

locked-rotor 430.6 (B)