Licensed Electrical Contractor Licensed Electrical Contractor Motors and Motor Controls Questions and Answers 3

Question 1

What happens to a three-phase induction motor if one phase of the supply is lost while the motor is running?

Accepted Answer

The motor continues to run at reduced power on single phase

Answer

The motor immediately stops and locks rotor

Answer

The motor reverses direction

Answer

The motor speed doubles on the remaining phases

Question 2

Which NEC article specifically covers the installation requirements for motor circuits and controllers?

Accepted Answer

Article 430

Answer

Article 410

Answer

Article 440

Answer

Article 480

Question 3

What is the purpose of a holding contact (seal-in contact) in a motor starter circuit?

Accepted Answer

To maintain the contactor coil circuit after the start button is released

Answer

To provide overload protection to the motor

Answer

To limit inrush current during starting

Answer

To disconnect the motor during a fault

Question 4

According to NEC 430.32, what is the maximum continuous motor overload protection setting for a motor with a marked service factor of 1.15 or greater?

Accepted Answer

125% of nameplate FLA

Answer

115% of nameplate FLA

Answer

130% of nameplate FLA

Answer

140% of nameplate FLA

Question 5

In a wye-delta motor starter, what is the primary advantage of starting the motor in the wye configuration?

Accepted Answer

Starting current is reduced to approximately one-third of delta starting current

Answer

The motor develops higher starting torque

Answer

The motor runs more efficiently at full load

Answer

It eliminates the need for overload protection

Question 6

What is the required grounding method for a motor frame per NEC 250.134?

Accepted Answer

An equipment grounding conductor run with the circuit conductors

Answer

A separate ground rod at the motor location only

Answer

A grounding electrode conductor from the motor to the service

Answer

Bonding to the building steel only