The hot wire carries electrical current from the source to the load and is always at a potential voltage relative to ground. Colored black, red, or blue depending on phase and system configuration, hot wires deliver power to HVAC equipment. A 240V air conditioning unit requires two hot wires; 120V control circuits use single hot wires.
Technical Details
Residential HVAC circuits typically operate at 15, 20, 30, or 50 amps, with corresponding wire gauges of 14 AWG, 12 AWG, 10 AWG, and 6 AWG respectively. Three-phase systems used in commercial HVAC installations utilize three hot wires, each 120 degrees out of phase. Hot wire voltage measurements from ground should read approximately 120V or 240V depending on configuration.
Practical Significance in HVAC
Hot wires remain dangerous even when equipment appears off, as they maintain voltage until the main disconnect is opened. HVAC technicians must use voltage testers before touching any circuit components. Circuit breakers protecting hot wires prevent overcurrent conditions that could damage compressors, blower motors, or heat pump components.