313D Electrical Components and Wiring 5

Question 1

Which electrical test would BEST confirm that a compressor motor winding has a ground fault?

Accepted Answer

Measure resistance between each winding terminal and the compressor shell/ground

Answer

A megohmmeter or ohmmeter reading between a winding terminal and the grounded shell detects insulation breakdown indicating a ground fault.

Question 2

A residential condensing unit's nameplate lists MOCP as 35 amps. A technician installs a 40-amp breaker. This installation is:

Accepted Answer

A code violation because the breaker exceeds the maximum listed on the nameplate

Answer

Installing a breaker larger than the MOCP listed on the nameplate violates NEC 440.22 and the unit's listing, removing the equipment's certified overcurrent protection.

Question 3

What is the purpose of the time-delay relay (TDR) found in some residential AC control circuits?

Accepted Answer

Prevents compressor short-cycling by enforcing a minimum off time between starts

Answer

A TDR enforces a compressor off-delay (typically 3–5 minutes) to allow pressures to equalize, preventing motor damage from trying to start against unequalized head pressure.

Question 4

When installing low-voltage thermostat wire, what is the minimum recommended AWG size for runs up to 100 feet?

Accepted Answer

18 AWG

Answer

18 AWG is the industry standard for thermostat wire runs up to approximately 100 feet, providing sufficient conductance to avoid excessive voltage drop in the 24V circuit.

Question 5

A residential AC system trips the breaker repeatedly after running for 10–15 minutes. The MOST likely electrical cause is:

Accepted Answer

Compressor drawing excessive amperage due to a failing motor or refrigerant overcharge

Answer

Thermal trip after a short run time typically indicates the compressor is drawing above-normal current, which could be caused by a failing motor winding or an overcharged refrigerant system.

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

313D Electrical Components and Wiring 5