Electrical and Controls for HVAC/R Equipment
Power and control wiring
NEC Article 440 governs HVAC and refrigeration equipment. Use the nameplate: minimum circuit ampacity (MCA) sets conductor size; maximum overcurrent protective device (MOCP) sets the breaker or fuse. A disconnect must be within sight of the equipment. Grounding and bonding are required; line-voltage work in Oregon requires the appropriate electrical license.
Controls
Low-voltage thermostats and Class 2 control circuits are common; verify transformer VA and wire the C-wire correctly. Sequence of operation matters: call for heat, ignition, blower delay, limit and rollout safeties. Do not bypass safety switches to diagnose a fault.
Worked example
Nameplate says MCA 24 A, MOCP 40 A. Choose conductors with ampacity at least 24 A and a 40 A breaker marked for the equipment. Do not install a 50 A breaker “for nuisance trips.” Verify the disconnect is within sight and the equipment grounding conductor is connected.
Traps
Oversizing the breaker beyond MOCP; using undersized wire on a long run; bypassing safeties; and mixing line and low voltage.