Electrical Components and Wiring Flashcards
7 cards from real 313D 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 Components and Wiring flashcards as text
A technician uses a clamp meter to measure current on one hot leg feeding a 240V condensing unit and reads 0 amps while the unit should be running. What should be checked FIRST?
Answer: Whether one leg of the breaker has tripped or lost power
Zero current on one leg of a 240V circuit most often indicates that leg's breaker has tripped or the utility has lost one phase at the panel.
Which component in a residential AC system provides low-voltage power to the thermostat and control board?
Answer: The 24V step-down control transformer
The control transformer steps 120V or 240V primary voltage down to 24V AC to power the thermostat, control board, and relay coils.
What is the correct procedure to verify that a capacitor is fully discharged before handling it?
Answer: Short the terminals together with an insulated screwdriver through a 20,000-ohm resistor
Discharging through a 20,000-ohm resistor limits the discharge current to a safe level while still fully draining the stored charge before handling.
In a residential air conditioning system, the low-voltage thermostat wire labeled 'Y' is used to signal:
Answer: Cooling demand to energize the compressor contactor
The Y wire carries the cooling call signal from the thermostat to the air handler or furnace control board, which then energizes the outdoor unit contactor.
Why is it important that the disconnect box for a residential condensing unit be located within sight of the unit?
Answer: To allow service technicians to lock out the unit while remaining in visual contact with it
NEC 440.14 requires a disconnect within sight of the unit so technicians can verify the unit is de-energized and prevent unexpected re-energization while servicing.
A motor nameplate shows FLA = 8A and SF = 1.15. What does the service factor (SF) indicate?
Answer: The motor can be operated continuously at 115% of its rated load without damage
A service factor of 1.15 means the motor can handle 15% above its rated load on a continuous basis without exceeding its thermal limits.
What happens to a run capacitor's capacitance value as it ages and begins to fail?
Answer: It decreases below its rated MFD
As a run capacitor ages, its dielectric deteriorates and capacitance decreases, reducing its ability to maintain motor efficiency and causing overheating.