Electrical Controls & Wiring Flashcards

What Canadian electrical code (CEC) requires HVAC technicians to follow when performing electrical work on refrigeration equipment?

Answer: The Canadian Electrical Code (CSA C22.1), adopted by all provinces and territories

The Canadian Electrical Code (CEC), published as CSA C22.1, is the primary electrical installation standard adopted by all Canadian provinces and territories and governs all electrical work including HVAC equipment wiring.

What is the purpose of the common terminal (C) on a 24V HVAC thermostat wiring connection?

Answer: To provide the return (neutral) path for the 24V control circuit, completing the circuit back to the transformer

The C terminal (common) provides the return path for 24V AC current back to the transformer secondary, completing the control circuit; without it, smart thermostats and WiFi thermostats cannot draw the power they need.

What does a ground fault circuit interrupter (GFCI) protect against in HVAC applications?

Answer: Electrical shock by detecting small leakage currents (as low as 5 mA) to ground and opening the circuit within milliseconds

A GFCI monitors the difference between current on the hot and neutral conductors; if even a small current (≥5 mA) is flowing to ground through a person or fault path, it trips in about 25 milliseconds, preventing lethal electric shock.

In a three-phase motor connection, what is the difference between a wye (star) and delta configuration?

Answer: Wye connects each winding between a line and a neutral point; delta connects each winding directly between two lines, resulting in different voltage across each winding

In a wye connection, one end of each winding meets at a neutral point and the other end connects to a line, so each winding sees line-to-neutral voltage; in a delta connection, each winding is connected line-to-line, so each winding sees full line voltage.

What does a current transformer (CT) do in an HVAC monitoring or protection system?

Answer: It produces a small secondary current proportional to the high primary current flowing through a conductor, allowing safe measurement and monitoring of large currents

A current transformer clamps around a conductor and inductively produces a proportional, much smaller secondary current (typically 0-5A AC) that is safe to connect to metering or protection relays without direct connection to the high-current circuit.

What is the purpose of the reversing valve in a heat pump system?

Answer: To redirect refrigerant flow so the indoor coil acts as a condenser (heating) or evaporator (cooling), switching the system between heating and cooling modes

The four-way reversing valve redirects refrigerant flow in the system so that the indoor coil can function as either a condenser (releasing heat for heating) or an evaporator (absorbing heat for cooling), giving the heat pump dual-mode capability.