CPM CPM - Certified Plant Mechanic Electrical Systems and Controls 2

Question 1

What is the primary function of a contactor in a motor control starter circuit?

Accepted Answer

Switch high-voltage power to the motor coil

Answer

A contactor is an electromechanically operated switch that connects and disconnects the main power supply to the motor based on control circuit signals.

Question 2

What does the abbreviation DOL stand for in motor starting methods?

Accepted Answer

Direct On Line

Answer

DOL (Direct On Line) starting connects the motor directly to full supply voltage, resulting in high inrush current at startup.

Question 3

A star-delta (Y-Δ) starter reduces motor starting current to approximately what fraction of the DOL value?

Accepted Answer

1/3

Answer

Star-delta starting reduces inrush current to approximately 1/3 of the DOL starting current by initially connecting windings in star configuration.

Question 4

What is the purpose of a control transformer in a motor starter panel?

Accepted Answer

Step down voltage to a safe level for the control circuit

Answer

A control transformer steps line voltage down (typically to 120 V or 24 V) to power the control components such as relay coils and pilot devices.

Question 5

Which type of motor control device allows a motor to run in both forward and reverse directions?

Accepted Answer

Reversing starter

Answer

A reversing starter uses two contactors wired so that energizing the second contactor swaps two of the three phase leads, reversing motor rotation.

CPM - Certified Plant Mechanic Practice Test

CPM - Certified Plant Mechanic Practice Test

CPM CPM - Certified Plant Mechanic Electrical Systems and Controls 2