High-Frequency GFCIs Reach the Market as the NEC's HVAC Exception Winds Down
For years, standard GFCI outlets and breakers have had an uneasy relationship with modern variable-speed HVAC equipment. Inverter-driven compressors and heat pumps can leak small amounts of high-frequency current during normal operation — not a dangerous fault, but often enough to trip a standard Class A GFCI. That incompatibility is what led the National Electrical Code to carry a delayed HVAC exception forward through the 2020 and 2023 cycles, according to trade coverage from sygfci.com, an electrical component sourcing publication.
That exception expires September 1, 2026, and manufacturers have been developing a purpose-built alternative in the meantime. A newer device category, Class C Special-Purpose GFCI (SPGFCI), evaluated under UL 943C rather than the standard UL 943, is now recognized specifically for equipment like HVAC compressors. Some of these devices carry an 'HF' or 'HF+' marking, according to an industry overview from IECI, indicating they're built with a trip curve that tolerates higher-frequency leakage current without nuisance-tripping, while still reacting to genuine low-frequency ground faults.
The distinction matters for anyone specifying or buying equipment ahead of the September deadline: a standard Class A GFCI and a Class C SPGFCI are not interchangeable, and per NEC guidance summarized by the Building Code Forum, any disconnect using SPGFCI protection for HVAC equipment must carry a specific warning label identifying it as such, so future inspectors and technicians know the correct protection path is in place.
For a homeowner whose only symptom is a GFCI that trips exclusively when the outdoor HVAC unit cycles on, this development is directly relevant: the fix is very likely a device-class mismatch rather than a wiring fault, and swapping to the right SPGFCI device is the code-compliant solution rather than removing protection altogether.
Homeowners experiencing this exact pattern can flag HVAC-related nuisance tripping directly in the TripTrace diagnostic to see how it scores against other possible causes.