The voltages of 600 V and lower are called low voltage, the voltages of 600 V-69 kV are called medium voltage, the voltages of 69 kV-230 kV are called high voltage and the voltages of 230 kV-1,100 kV are called high voltage, with 1,100 kV is also called high voltage.

The electric ranges and furnaces require a line voltage from 220 to 240 volts to 60 hertz, commonly called 220 volt output.

In addition, contacts and relays operate in the same way in a typical HVAC control circuit. Both are normally controlled by 24 volts and usually switch the voltage from the line to an engine or compressor.

The engine is normally powered by the same 24 volt AC power supply that is used for the rest of the control system. This allows you to control the area valves directly with low voltage thermostats and low voltage cables. This type of valve requires the use of a SPDT thermostat or relay.

A typical U.S. domestic voltage is 120240 V, 60 Hz, a single phase. There is a tolerance and the real measured voltage is rarely exactly 120 volts. A common reading in my home is 117 volts.