UL 60335-2-40: What HVAC OEMs and panel builders need to know

UL 60335-2-40 is the North American safety standard for electrical heat pumps, air conditioners, and dehumidifiers — and the standard that governs how HVAC equipment safely uses today’s mildly flammable A2L refrigerants. Here’s what it covers, why it reshaped equipment design, and what OEMs and panel builders should verify with their component suppliers.

What is UL 60335-2-40?

UL 60335-2-40 is the product safety standard for electrically operated heat pumps, air conditioners, and dehumidifiers sold in North America, with new listings required to comply since January 1, 2024. It addresses protection against electrical shock, fire, and mechanical hazards — and, most consequentially for modern equipment design, it defines the safety requirements for systems using flammable refrigerants. The standard ensures safe handling of low-GWP A2L refrigerants, which require stricter mitigation to prevent ignition than the refrigerants they replaced.

Why the standard matters: the A2L transition

The refrigerant change itself is driven by regulation, not by UL: the EPA’s AIM Act phases down high-GWP HFC refrigerants, which pushed the industry from legacy refrigerants like R-410A to low-GWP A2L options such as R-454B and R-32. With R-410A equipment no longer manufactured or imported for the U.S. market since January 1, 2025, A2L systems are now the norm in new residential and light commercial equipment.

What UL 60335-2-40 does is govern how equipment uses these refrigerants safely. The standard does not require A2L refrigerants — the EPA drives the transition; UL 60335-2-40 defines how equipment using them must be built. Because A2Ls are classified as mildly flammable, the standard imposes requirements that earlier HVAC equipment never faced: limits on refrigerant charge, leak detection and mitigation provisions, and scrutiny of anything inside the equipment that could act as an ignition source.

What the standard means for components inside the panel

For OEMs and panel builders, the ignition-source requirements are where UL 60335-2-40 reaches deepest into the bill of materials. Switching devices — from compact definite purpose contactors handling compressor and fan duty to large general-purpose contactors — receive particular attention, because an arc inside an enclosure where leaked refrigerant could accumulate is a potential ignition source. Components in these applications must be tested to verify they cannot serve as an ignition source in an A2L atmosphere.

This is especially important for larger contactors with a wider air gap, which have an increased risk of ignition in the system. Because these components are inherently more likely to generate a point of ignition, they require more stringent testing — and only a few third-party labs globally can accommodate testing of large contactors with a 110mm frame and up. Sourcing from suppliers that have already completed certification removes the longest-lead-time item from the critical path.

What OEMs and panel builders should do now

With the transition deadlines behind the industry, the compliance question has shifted from “will my supplier be ready” to “is compliance documented in everything I specify.” Three habits keep platforms clean:

• Ask suppliers to confirm, in writing, that switching components are tested or certified to UL 60335-2-40’s component requirements, alongside traditional standards like UL, CSA, and IEC 60947-4-1.
• Make that documentation a standard line item in sourcing requirements, not a one-time check.
• When redesigning platforms for new refrigerants or efficiency targets, treat component qualification as part of the design schedule rather than a procurement afterthought — certified components specified early prevent certification surprises late.

Working with suppliers that completed certification ahead of the transition — such as ABB, whose contactor families were certified to the standard before the deadline — gives OEMs the documentation and component availability to keep their own equipment certifications on schedule.

A standard that will keep evolving

UL 60335-2-40 continues to be revised as refrigerant regulations tighten and field experience accumulates, and the A2L transition it enabled is unlikely to be the last. OEMs and panel builders that build documented component compliance into their standard sourcing practice — rather than treating each standards change as a one-off scramble — will be positioned to absorb the next revision without disruption.

See related posts: “Definite Purpose Contactors: 5 Sourcing Considerations for HVAC OEMs“

Common questions about UL 60335-2-40

This article was originally published in August 2023 and was updated in June 2026 to reflect the standard now being in effect.

Author

Will Hulbert, Product Marketing Manager – Contactors, Manual Motor Starters, and Overload Relays · ABB Electrification Business

Will Hulbert is the U.S. Product Marketing Manager for Contactors, Manual Motor Starters, and Overload Relays at ABB Electrification’s Smart Power division, where he is responsible for overall product strategy, positioning, and commercialization in the U.S. market. Will’s background is in servo motor and control automation, with a passion for robotics and new innovations.