313A Electrical Controls & Wiring

Question 1

What is the purpose of a contactor in an HVAC electrical circuit?

Accepted Answer

To act as an electrically operated switch that uses a low-voltage control coil to open and close high-voltage power contacts to the compressor or fan motor

Answer

To measure and display voltage and current to the compressor

Answer

To protect against ground faults in the power supply

Answer

To convert single-phase power to three-phase power for the compressor

Question 2

What does a thermal overload relay do in a motor starter circuit?

Accepted Answer

It senses motor current and opens the control circuit if sustained overcurrent is detected, protecting the motor from overheating due to overload

Answer

It measures motor winding temperature directly and shuts down on overtemperature

Answer

It provides power factor correction for the motor

Answer

It reverses motor rotation if the motor starts in the wrong direction

Question 3

In Canadian HVAC wiring, what voltage is most commonly used for low-voltage control circuits?

Accepted Answer

24 V AC

Answer

12 V DC

Answer

48 V AC

Answer

120 V AC

Question 4

What is the function of a high-pressure safety control (high-pressure cutout) in a refrigeration system?

Accepted Answer

To shut down the compressor if discharge pressure exceeds a safe limit, preventing equipment damage and refrigerant venting

Answer

To prevent the condenser fan from operating when ambient temperature is too high

Answer

To limit the maximum current draw of the compressor motor

Answer

To signal a low refrigerant charge condition to the building management system

Question 5

What does a phase-loss relay protect against in a three-phase compressor installation?

Accepted Answer

Detecting the loss of one phase of the three-phase supply, which would cause the motor to overheat and potentially burn out

Answer

Protecting the compressor from reverse rotation due to miswired phases

Answer

Preventing the compressor from starting when the power supply frequency is out of range

Answer

Protecting against voltage spikes from lightning or utility switching

Question 6

What is the purpose of a lockout-tagout (LOTO) procedure when servicing HVAC equipment in Canada?

Accepted Answer

To isolate and lock all energy sources (electrical, refrigerant pressure, etc.) to prevent unexpected re-energization during maintenance, protecting the technician from injury

Answer

To lock the thermostat at a fixed temperature to prevent tampering during service

Answer

To seal the refrigerant circuit to prevent leaks during transport

Answer

To record service work completed on a tag attached to the equipment