NATE Electrical and Controls 2

Question 1

A contactor coil is rated at 24V AC. If the supply voltage to the coil drops to 18V AC, what is the MOST likely result?

Accepted Answer

The contactor may chatter or fail to fully close

Answer

Insufficient coil voltage prevents full magnetic engagement, causing the contactor to chatter or fail to close completely.

Question 2

What is the function of a run capacitor in a PSC (permanent split capacitor) motor?

Accepted Answer

Improve power factor and running efficiency

Answer

A run capacitor creates a phase shift in the auxiliary winding that improves power factor and running efficiency throughout operation.

Question 3

What does a lockout/tagout (LOTO) procedure require before servicing electrical HVAC equipment?

Accepted Answer

Isolating and de-energizing the power source and verifying zero energy state

Answer

LOTO requires disconnecting and locking the energy source, then verifying zero energy state before any service work begins.

Question 4

On a cooling thermostat, which terminals are energized when the system is calling for cooling?

Accepted Answer

R and Y

Answer

During a cooling call, the Y (compressor) terminal is energized along with R (power), activating the compressor contactor.

Question 5

What does a megohmmeter (megger) measure?

Accepted Answer

Insulation resistance of motor windings

Answer

A megohmmeter applies high DC voltage to measure insulation resistance, revealing breakdown or moisture in motor windings.

NATE - North American Technician Excellence Practice Test