309A Motor Controls 2

Question 1

What must be done to reverse the direction of a three-phase motor?

Accepted Answer

Reverse any two of the three supply leads

Answer

Reverse all three supply leads

Answer

Change the motor's internal capacitor

Answer

Reduce the supply voltage by half

Question 2

What is an interlock in a motor reversing starter circuit?

Accepted Answer

A device that prevents both forward and reverse contactors from being energized simultaneously

Answer

A mechanical lock on the enclosure door

Answer

A thermal switch that monitors motor temperature

Answer

A timing relay for sequential starting

Question 3

What is the function of a variable frequency drive (VFD) in a motor control system?

Accepted Answer

To control motor speed by varying the frequency and voltage of the power supply

Answer

To provide overcurrent protection only

Answer

To convert single-phase power to three-phase power only

Answer

To provide power factor correction only

Question 4

According to the CEC, what is the minimum conductor size for a motor branch circuit supplying a motor with an FLC of 28 A?

Accepted Answer

No. 10 AWG

Answer

No. 14 AWG

Answer

No. 12 AWG

Answer

No. 8 AWG

Question 5

What does a motor's nameplate 'code letter' indicate?

Accepted Answer

The locked-rotor kVA per horsepower

Answer

The motor's efficiency rating

Answer

The motor's service factor

Answer

The insulation class

Question 6

What type of motor starter provides reduced voltage starting through a series of resistors?

Accepted Answer

Primary resistor starter

Answer

Across-the-line starter

Answer

Wye-delta starter

Answer

Soft starter