Outdoor HVAC GFCI requirement: what Minnesota is seeing

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For several years, the HVAC industry has wrestled with unwanted tripping associated with GFCI protection required by Section 210.8(F) of the National Electrical Code (NEC). Time’s up. On September 1 the NEC requires GFCI protection for outdoor HVAC systems via the expiration of No. 2 exception for outdoor HVAC.

September 1 has now come and gone.

Minnesota provides one of the first opportunities for ACCA to ask a simple question: What is actually happening in the field?

Enforcement is limited

It is important to understand Minnesota’s enforcement is focused on new construction only. The state does not require GFCI protection for replacement of existing HVAC equipment when the existing feeder or branch circuit has not been altered or extended. Routine HVAC change-outs are unaffected.

That distinction matters when interpreting Minnesota’s early experience: the state has received no reports of HVAC GFCI compatibility problems since September 1, but the number and mix of affected installations are not yet known.

Minnesota’s experience so far

 Minnesota is now enforcing the NEC outdoor HVAC GFCI requirement for applicable new installations following expiration of the exception on September 1.

ACCA contacted Dean Hunter, Assistant Director and Chief Electrical Inspector for the Minnesota Department of Labor and Industry (DLI), to learn how the requirement is working in practice.

It’s too early to tell.

According to Hunter, Minnesota has received no reports of HVAC GFCI compatibility problems since the September 1 expiration of the exception. That does not establish that no problems have occurred, only that none have been reported to the state. Hunter also reports significant use of newer high-frequency (HF) GFCI devices. Before September 1, Minnesota had a procedure for dealing with unwanted tripping.

Contractors or homeowners experiencing compatibility problems could submit an “unwanted-tripping report” to the National Electrical Manufacturers Association (NEMA). With documentation that the report had been filed, GFCI protection could be removed while the compatibility problem was addressed. With no reported HVAC problems under the new requirement so far, Minnesota does not currently have a comparable post-September 1 removal protocol. Hunter told ACCA that if an incident occurs, the state will address it on a case-by-case basis.

The absence of reports is useful information, but it is still early.

 What does “HF” actually mean?

The emergence of HF-rated GFCIs is an important part of this story.

UL Solutions developed Supplement SB to UL 943 after compatibility problems were identified between some appliances—including HVAC equipment—and conventional GFCIs. The supplemental procedure evaluates GFCI immunity in the presence of high-frequency signals and is intended to improve interoperability with equipment containing power-conversion technology such as variable-speed drives and inverters.

The 2026 NEC now recognizes HF and HF+ devices in an informational note associated with Section 210.8(F). Minnesota’s own summary of the 2026 NEC identifies these devices as an option for addressing high-frequency (HF) interoperability concerns.

But there is an important distinction.

An HF designation means the device has been evaluated using the applicable tests in the UL standard. It does not mean every possible cause of unwanted HVAC GFCI tripping has been eliminated. High-frequency leakage is one compatibility issue. There may be other equipment characteristics, operating conditions, installation conditions, or electrical phenomena that can cause a GFCI to operate.

Likewise, individual manufacturers may design equipment or protective devices with features that go beyond the minimum requirements of a product standard.

Product standards are developed through engineering analysis, laboratory testing, and consensus-based technical evaluation. As equipment technologies evolve, additional research, testing and field experience can help refine those standards and improve interoperability.

What equipment is behind Minnesota’s early results?

There is another reason to be careful about drawing broad conclusions from Minnesota’s early reports: we do not yet know the equipment mix represented by those installations.

Today’s new HVAC equipment increasingly incorporates variable-speed and inverter technology—the types of power electronics specifically associated with the high-frequency compatibility issue addressed by the HF test.

What about conventional single-stage equipment? What about different manufacturers and equipment combinations? What about different installation configurations?

And what happens over a full cooling and heating season rather than during the first month of enforcement?

“No reported problems” is meaningful information. But without knowing the number of installations behind that statement, it cannot tell us how every type of HVAC equipment will perform.

The Code, the Standard and the AHJ are not the same thing

A product standard, the NEC, and an Authority Having Jurisdiction (AHJ) perform different jobs.

UL 943 establishes requirements and testing procedures used to evaluate GFCIs. The NEC establishes where GFCI protection is required and references applicable product standards. State and local authorities adopt electrical codes, while the AHJ administers and enforces the adopted requirements.

Then contractors comply with the code and the standard in the real world.

A product can comply with its applicable UL standard. An installation can comply with the NEC. An inspector can correctly enforce the adopted code.

And field experience can still reveal something that wasn’t anticipated.

That does not necessarily mean the product standard failed, the NEC failed, or the AHJ got it wrong. It means an unexpected condition has been identified. Contractors’ documented experience can provide important feedback for maintaining effective codes and improving requirements that cause unintended problems.

What contractors can tell us

Laboratory evaluation establishes how protective devices perform under defined test conditions. Reports from actual installations can help identify which equipment and GFCI combinations are working reliably, and where further investigation may be warranted. That feedback strengthens the evidence available to manufacturers, standards developers, and code officials, without diminishing the importance of product testing.

ACCA will continue talking with contractors, manufacturers, code officials, and other industry stakeholders as more installations accumulate and more field experience becomes available.

ACCA encourages contractors to document their experiences with outdoor HVAC GFCI installations, including the HVAC equipment involved, protective devices used, and any compatibility problems encountered. Reports of successful installations are valuable, too.

Such information can help the industry assess emerging solutions and support improvements to codes and standards.

The important question is whether HF GFCIs can provide the required personnel protection while operating reliably with the range of HVAC equipment and installation configurations encountered in the field.

Understanding successful installations and documented compatibility problems can help manufacturers, standards developers and code officials determine whether further improvements are necessary.

That is how better products are developed, better standards are written and better codes evolve.

Contractors can access ACCA’s GFCI resource center any time at www.acca.org/GFCI.

Please contact ACCA’s manager of codes at david.bixby@acca.org if you have any questions or would like to share some field data or enforcement information.

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Posted In: Electrical, Field Safety, Residential, Residential Buildings, Residential Equipment, Safety, Uncategorized, Workplace Safety