Since then, significant work has been completed by the HVAC and electrical industries to better understand this issue.

Looking Back
When NEC 210.8(F) was first introduced, many contractors, inspectors, manufacturers, and homeowners began reporting instances where HVAC equipment would repeatedly trip GFCI devices despite no apparent ground fault being present.

The reports were particularly common with modern inverter-driven equipment, including variable-speed air conditioners and heat pumps.

At the time, opinions varied regarding the underlying cause. Some believed the issue was related to equipment design. Others suspected differences between GFCI manufacturers. The industry lacked sufficient data to determine exactly why these trips were occurring.

For that reason, the HVAC industry requested and received a temporary exemption that would allow time for research and analysis.

What Has Been Learned
To better understand the issue, AHRI partnered with EPRI to perform extensive testing under Project 8029.

The recently published Phase II report represents one of the most comprehensive investigations of HVAC and GFCI compatibility performed to date.

AHRI Report 8029-02 (PDF)

The research demonstrated that nuisance tripping is not typically the result of a single defect or a single manufacturer.

Instead, compatibility is influenced by the interaction between:

• Modern inverter-driven HVAC equipment
• High-frequency leakage current characteristics
• The filtering and sensing methods used by individual GFCI designs
  

The research also demonstrated that compatibility is highly dependent on the interaction between a specific HVAC system and a specific GFCI design, reinforcing that no single component can be identified as the sole cause of nuisance tripping. One of the more important findings was that performance varied significantly among GFCI devices, particularly when exposed to the high-frequency current components commonly produced by modern power electronic equipment.

A Different Situation Than Before
Several years ago, the industry's request was simple: provide time to understand the problem. Today, the situation is different.

The research has provided valuable answers and identified practical paths toward resolution.

The challenge is no longer understanding the problem; it is implementing the solutions.

For HVAC manufacturers, that includes:

• Updating product designs where necessary
• Completing testing and validation
• Obtaining NRTL certifications
• Implementing manufacturing changes
  

For GFCI manufacturers and standards organizations, work also remains.

High-frequency compatible GFCI devices have been introduced by some manufacturers, while others have publicly indicated that development efforts remain ongoing. Even as these products are brought to market, broad availability and adoption throughout the electrical supply chain will take time. In addition, work within UL 943 continues as industry stakeholders evaluate the lessons learned from recent research and real-world experience. UL 943 currently includes optional high-frequency performance requirements, and work is underway to incorporate mandatory high-frequency requirements into a future revision of the standard. That work remains ongoing.

Why Additional Time Is Being Requested
AHRI has submitted TIA 1924, which would extend the HVAC equipment exemption currently associated with NEC 210.8(F) through September 1, 2028. The proposal is intended to provide time for the findings of Project 8029 to be incorporated into equipment designs, product standards, certification programs, and commercially available GFCI products.

The long-term objective remains the same: safely and reliably applying GFCI protection to HVAC equipment.

The request recognizes that research, standards development, product redesign, certification activities, manufacturing implementation, and market adoption all occur on different timelines.

Simply put, the industry spent the last several years understanding the problem. The next phase is implementing the solutions identified by that work.

Moving Forward
The HVAC and electrical industries share the same goal: Safe, reliable electrical installations.

The HVAC industry requested time to understand this issue, and the research effort has significantly advanced that understanding. The industry's focus is now shifting from investigation to implementation, with the shared goal of achieving safe, reliable, and practical GFCI protection for modern HVAC equipment.

As standards evolve, products are updated, and high-frequency tolerant GFCI devices become more widely available, the lessons learned from this research will help guide the path forward for manufacturers, inspectors, contractors, and end users alike.

Thanks,

Cullen E. Hall
Corporate Principal Electrical Engineer
Cullen.Hall@daikinapplied.com