FREE Journeyman Electrician’s Motors and Motor Controls Questions and Answers

Question 1

An electrician is installing a branch circuit for a 10 HP, 230V, 3-phase, continuous-duty induction motor.
The motor will be supplied with 75°C rated THWN copper conductors.
According to the NEC, what is the minimum size for these branch-circuit conductors?

Accepted Answer

10 AWG

Answer

12 AWG

Answer

8 AWG

Answer

6 AWG

Question 2

A 460V, three-phase motor has a nameplate full-load current (FLA) of 52A, a service factor of 1.15, and a temperature rise not over 40°C. What is the maximum permitted rating for a separate overload protection device?

Accepted Answer

65A

Answer

52A

Answer

59.8A

Answer

70A

Question 3

Which of the following is the maximum standard size non-time-delay fuse that can be used for branch-circuit, short-circuit, and ground-fault protection for a 25 HP, 460V, 3-phase, squirrel-cage motor?

Accepted Answer

110A

Answer

100A

Answer

90A

Answer

125A

Question 4

An electrician is installing a motor on a rooftop air-conditioning unit. The motor controller is located inside a mechanical room on the floor below. According to the NEC, what is required for the disconnecting means?

Accepted Answer

A disconnecting means must be located in sight from the motor.

Answer

A circuit breaker in a panelboard on the same floor is sufficient.

Answer

The disconnect at the controller must simply be lockable.

Answer

A horsepower-rated switch must be installed within 25 feet of the motor.

Question 5

When a motor control circuit is tapped from the load side of the motor's branch-circuit protective device, what is the primary factor used to determine if the control circuit conductors require their own supplementary overcurrent protection?

Accepted Answer

The rating of the motor's branch-circuit protective device.

Answer

The horsepower rating of the motor.

Answer

The length of the control circuit conductors.

Answer

The voltage of the control circuit.

Question 6

A feeder supplies a group of three-phase, 460-volt continuous-duty motors with the following full-load currents (FLC) taken from NEC tables: 52A, 21A, and 14A. What is the minimum required ampacity for the feeder conductors?

Accepted Answer

100A

Answer

87A

Answer

110A

Answer

93.5A