Electrical and Controls Flashcards
7 cards from real NATE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical and Controls flashcards as text
What is the standard line voltage for most residential HVAC equipment in the United States?
Answer: 240V/60Hz
Most residential HVAC equipment in the US operates on 240V single-phase 60Hz power.
Which component in an HVAC control circuit is used to sense thermostat demand and energize the compressor contactor?
Answer: Control relay
A control relay receives the low-voltage thermostat signal and switches the higher-voltage circuit to energize the compressor contactor.
What does the label 'R' on an HVAC thermostat terminal typically represent?
Answer: 24V AC power from the transformer
The 'R' terminal supplies 24V AC power from the control transformer to the thermostat and control circuit.
A single-phase motor fails to start and hums loudly. Which component is MOST likely the cause?
Answer: Start capacitor
A failed start capacitor prevents the phase shift needed for starting torque, causing the motor to hum without starting.
What is the purpose of a high-pressure cutout switch in an HVAC system?
Answer: Protect the compressor from excessive discharge pressure
A high-pressure cutout switch opens the control circuit when discharge pressure exceeds a safe limit, protecting the compressor from damage.
When measuring AC voltage with a multimeter, what type of reading does a standard digital multimeter display?
Answer: RMS (root mean square) voltage
Standard digital multimeters display RMS voltage, which represents the effective value of AC voltage equivalent to DC.
Which wire color in a standard NEC-compliant 120V residential wiring system is the grounded conductor (neutral)?
Answer: White
Per NEC, white (or gray) is the grounded conductor (neutral) in a standard 120V residential wiring system.