IEC - Independent Electrical Contractors Motors and Motor Controls Questions and Answers

Question 1

An electrician is installing a single continuous-duty 10 HP, 230V, 3-phase motor.
According to the NEC tables, its Full Load Current (FLC) is 28A.
The motor has a service factor of 1.15 and its nameplate FLA is 26A.
What is the maximum standard size for the separate overload protection device?

Accepted Answer

32.5A

Answer

30A

Answer

35A

Answer

28.75A

Question 2

According to NEC 430.102(B), a disconnecting means for a motor must be located in sight from the motor and the driven machinery. Which of the following meets the NEC definition of 'in sight from'?

Accepted Answer

Visible and not more than 50 feet distant from the other.

Answer

On the opposite side of a permanent wall, but directly behind the motor.

Answer

Visible and not more than 100 feet distant from the other.

Answer

Unobstructed, but located on the floor above the motor.

Question 3

A motor control circuit is tapped from the load side of a motor's branch-circuit short-circuit and ground-fault protective device. According to NEC 430.72(B) and Table 430.72(B)(2), what is the primary factor in determining the maximum rating of the overcurrent device for the control circuit conductors?

Accepted Answer

The conductor size (AWG) and whether it extends beyond the enclosure.

Answer

The horsepower rating of the motor.

Answer

The voltage of the control circuit.

Answer

The type of motor controller (e.g., manual or magnetic).

Question 4

An electrician needs to connect two 1/2 HP, 120V motors on a single 20A branch circuit in a workshop. The FLC for each motor is 9.8A, but the nameplate FLA is 5.8A. Under what condition is this installation permitted by NEC 430.53(A)?

Accepted Answer

The nameplate FLA of each motor does not exceed 6 amperes, and each motor has individual overload protection.

Answer

The branch-circuit protective device rating is not exceeded, and the FLC of each motor is less than 10A.

Answer

As long as the combined FLC (11.6A) is less than 80% of the breaker rating.

Answer

This installation is never permitted; each motor requires its own branch circuit.

Question 5

Which of the following is a primary function of a motor controller, as defined by the NEC?

Accepted Answer

To start and stop the motor, and interrupt the locked-rotor current.

Answer

To protect the motor from short-circuits and ground-faults.

Answer

To provide thermal overload protection based on the motor's service factor.

Answer

To serve as the primary disconnecting means for the branch circuit.

Question 6

The current a motor draws at the instant of starting when full voltage is applied, before the rotor begins to turn, is known as what?

Accepted Answer

Locked-Rotor Current (LRC)

Answer

Full-Load Current (FLC)

Answer

Service Factor Current (SFC)

Answer

In-service Amperage (ISA)