CRST Electrical Systems & Controls Flashcards
6 cards from real CRST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CRST Electrical Systems & Controls flashcards as text
What does a high-pressure control (HPC) do in a refrigeration system?
Answer: Shuts down the compressor when discharge pressure exceeds the set point
A high-pressure control monitors discharge pressure and shuts down the compressor if pressure exceeds a preset safety limit to prevent equipment damage.
In a refrigeration ladder diagram, what symbol represents a normally open (NO) contact?
Answer: Two parallel vertical lines with a gap between horizontal lines
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.
What is the purpose of a potential relay used with a refrigeration compressor motor?
Answer: Remove the start capacitor from the circuit once the motor reaches running speed
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.
What is the correct procedure before working on energized refrigeration electrical panels according to NFPA 70E?
Answer: Perform an arc flash risk assessment and wear appropriate PPE
NFPA 70E requires an arc flash risk assessment and appropriate arc-rated PPE before working on or near energized electrical equipment.
A three-phase compressor motor that hums but does not start is most likely experiencing which problem?
Answer: Single-phasing — loss of one supply phase
Single-phasing (loss of one phase) causes a three-phase motor to hum without starting because it cannot produce sufficient rotating magnetic field torque.
What does a low-pressure control (LPC) typically do in a commercial refrigeration system?
Answer: Cycle the compressor off when suction pressure drops below the set point
A low-pressure control cycles the compressor off when suction pressure drops below a set point, protecting the system from operating in a deep vacuum or refrigerant loss condition.