Licensed Electrical Contractor Motors and Motor Controls Questions and Answers

Question 1

A contractor is installing a single continuous-duty, 3-phase, 460V, 25 HP squirrel-cage induction motor.
According to NEC Table 430.250, the motor has a Full Load Current (FLC) of 34A.
What is the minimum required ampacity for the branch-circuit conductors?

Accepted Answer

42.5A

Answer

34A

Answer

38A

Answer

50A

Question 2

Which of the following is the primary value used to determine the size of branch-circuit short-circuit and ground-fault protection for a motor, according to NEC 430.6(A)(1)?

Accepted Answer

The motor's Full Load Current (FLC) from NEC Tables 430.247-430.250

Answer

The motor's nameplate Full Load Amperes (FLA)

Answer

The motor's locked-rotor current

Answer

The service factor adjusted amperage

Question 3

A motor controller for a 480V motor is located in an electrical room. According to NEC 430.102(B), the disconnecting means for the motor must be located in sight from the motor and the driven machinery. What is the maximum distance the disconnect can be from the motor to be considered 'in sight'?

Accepted Answer

50 feet

Answer

25 feet

Answer

100 feet

Answer

75 feet

Question 4

A motor with a nameplate service factor of 1.15 and a nameplate current rating of 20A is installed for continuous duty. What is the maximum rating for a separate overload protection device for this motor?

Accepted Answer

25A

Answer

20A

Answer

23A

Answer

30A

Question 5

When sizing a feeder that supplies two continuous-duty motors, how is the overcurrent protective device (OCPD) for the feeder determined according to NEC 430.62(A)?

Accepted Answer

Take the rating of the largest motor's branch-circuit short-circuit and ground-fault protective device and add the FLC of the other motor.

Answer

Sum the FLC of both motors and multiply by 125%.

Answer

Sum the ratings of the branch-circuit OCPDs for both motors.

Answer

Take 125% of the largest motor's FLC and add 100% of the other motor's FLC.

Question 6

Which of the following components in a motor circuit is specifically designed to protect the motor and conductors from excessive heating due to motor overloads and failure to start?

Accepted Answer

Overload relay (heater)

Answer

Inverse-time circuit breaker

Answer

Time-delay fuse

Answer

Main bonding jumper