Electrical Components and Wiring Flashcards
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Read the first 7 Electrical Components and Wiring flashcards as text
What does a high-pressure switch do in the electrical circuit of a residential air conditioner?
Answer: Opens the control circuit if refrigerant pressure exceeds a safe limit
A high-pressure switch is a normally closed safety device that opens the control circuit—de-energizing the compressor—when discharge pressure exceeds a preset limit.
Which NEC article primarily governs the installation of air-conditioning and refrigerating equipment?
Answer: Article 440
NEC Article 440 specifically addresses air-conditioning and refrigerating equipment, including motor-compressor branch circuit sizing and protection requirements.
A technician finds that a condenser fan motor runs but the compressor does not start and hums loudly. The MOST likely electrical cause is:
Answer: Open run capacitor for the compressor
A failed run capacitor reduces starting torque, causing the compressor to hum and fail to start while still drawing locked-rotor amperage.
What is the function of the crankcase heater in an air conditioning system, and how is it typically wired?
Answer: Keeps oil warm to prevent refrigerant migration; wired to be energized when the compressor is OFF
A crankcase heater prevents liquid refrigerant from migrating into compressor oil during off cycles; it is wired so it energizes whenever the compressor contactor is open.
When measuring voltage across a closed contactor's load-side terminals, a technician reads 5V instead of 0V. This most likely indicates:
Answer: Pitted or burned contacts causing excessive resistance
A voltage drop across a closed contactor indicates high contact resistance from pitting or burning, which causes heat and inefficient power delivery to the compressor.
A residential split system requires a dedicated 240V, 2-pole circuit breaker. What is the primary reason a 2-pole breaker is required instead of two single-pole breakers?
Answer: A 2-pole breaker ensures simultaneous disconnection of both hot legs during a fault
A 2-pole breaker trips both hot conductors simultaneously, ensuring the full 240V circuit is de-energized during an overcurrent event for safe protection.
What does the term 'locked-rotor amperage' (LRA) mean in the context of an AC compressor?
Answer: The maximum current drawn at the instant of startup before the motor reaches running speed
LRA is the high inrush current a motor draws at startup when the rotor is stationary, which can be 5–8 times the full-load running amperage.