NFPA 70, the National Electrical Code (NEC), governs all electrical installations in the United States including HVAC equipment wiring. HVAC systems have specific NEC requirements covering disconnect switches, circuit sizing, grounding, equipment protection, and wiring methods.
Key NEC requirements for HVAC include: a dedicated disconnecting means within sight of the equipment (Article 440), minimum circuit ampacity at 125% of the nameplate current, maximum overcurrent protection as specified on the nameplate, proper grounding of all equipment, and appropriate wire gauge for the circuit ampacity.
HVAC technicians must understand basic NEC requirements for their work, but major electrical work should be performed or supervised by a licensed electrician. Permits and inspections are required for new HVAC electrical installations in virtually all jurisdictions. Improper electrical connections are a leading cause of HVAC equipment fires and premature component failure.