CRST CRST Electrical Systems & Controls 2

Question 1

What does a high-pressure control (HPC) do in a refrigeration system?

Accepted Answer

Shuts down the compressor when discharge pressure exceeds the set point

Answer

A high-pressure control monitors discharge pressure and shuts down the compressor if pressure exceeds a preset safety limit to prevent equipment damage.

Question 2

In a refrigeration ladder diagram, what symbol represents a normally open (NO) contact?

Accepted Answer

Two parallel vertical lines with a gap between horizontal lines

Answer

A normally open contact is represented by two parallel vertical lines separated by a gap across the circuit path, indicating the contact is open in its de-energized state.

Question 3

What is the purpose of a potential relay used with a refrigeration compressor motor?

Accepted Answer

Remove the start capacitor from the circuit once the motor reaches running speed

Answer

A potential relay senses the back-EMF generated by the start winding and opens its contacts to remove the start capacitor once the motor reaches approximately 75% of operating speed.

Question 4

What is the correct procedure before working on energized refrigeration electrical panels according to NFPA 70E?

Accepted Answer

Perform an arc flash risk assessment and wear appropriate PPE

Answer

NFPA 70E requires an arc flash risk assessment and appropriate arc-rated PPE before working on or near energized electrical equipment.

Question 5

A three-phase compressor motor that hums but does not start is most likely experiencing which problem?

Accepted Answer

Single-phasing — loss of one supply phase

Answer

Single-phasing (loss of one phase) causes a three-phase motor to hum without starting because it cannot produce sufficient rotating magnetic field torque.

(CRST) Certified Refrigeration Service Technician Practice Test

(CRST) Certified Refrigeration Service Technician Practice Test

CRST CRST Electrical Systems & Controls 2