Electrical Component Considerations for A2L System Safety

In the transition to lower-GWP refrigerants, specifying engineers and contractors play an essential role in helping retailers make next-generation equipment decisions. Among the emerging alternatives, A2L refrigerants will likely have a place in both self-contained and remote system architectures. With available options below 150 and 300 GWP, A2Ls can help end users meet the Environmental Protection Agency’s (EPA’s) GWP limits across numerous sectors.

Unique Considerations

As a new refrigerant in the commercial refrigeration sector, the A2L “lower flammability” classification comes with unique considerations. To ensure safety and alleviate retailers’ other concerns as well, specifying engineers and contractors must educate themselves on new safety requirements and risk mitigation measures pertaining to applications, equipment, and component designs.

Ensuring electrical system safety compliance is a chief design consideration with A2L-optimized equipment, as powered electrical components could be potential ignition sources upon contact with a flammable concentration of gas. The Underwriters Laboratories (UL) 60335-2-89, 2^nd edition safety standard provides guidelines for the safe use of flammable A3 and A2L refrigerants in commercial refrigeration equipment, including requirements for electrical components.

The UL 60335-2-89, 2^nd edition standard establishes design strategies based on the lower flammability limit (LFL) of an A2L, which includes charge limit allowances, leak rates, and detection requirements. LFL is based on the worst-case formulation (WCF) — or maximum refrigerant burning velocity — of all A2L refrigerants being considered for approval.

• Relays/contactors and/or devices used for switching electrical currents on/off;
• Controllers;
• Variable-frequency drives (VFDs); and
• Electrical enclosure (box) within which a full system may be contained.

Design Strategies

• Protected systems are those in which no part of the cooling system is inside the food storage compartment. Safety measures must be designed to ensure that refrigerant leaks will not pose a fire or explosion hazard. This is typically achieved by containing the refrigerant system into an enclosure such that leaked gas cannot reach the food storage area.
• Unprotected systems are appliances in which at least one part of the cooling system is placed inside a food storage compartment. Because a refrigerant leak could create conditions for an explosion near electrical components, these systems must be designed with additional safety measures. This can include special certifications for individual components or an overall system-level certification.

For unprotected systems, A2L safety compliance and/or certification may be achieved either through individual component-level certification or at a higher level that encompasses the entire system in an electrical enclosure. Only one certification approach is necessary to achieve compliance; Copeland is currently qualifying its electrical components for individual certification.

For individual component level certification, per UL 60335-2-89, 2^nd edition, Annex 101.DVL, electrical components, relays, or devices used on appliances designed for A2Ls must adhere to tight enclosure tolerances. These requirements are also in accordance with UL 60079-15 standard (Clause Annex BB) for non-sparking electrical apparatus.

Essentially, the maximum size of openings — physical gaps (i.e., holes) in a device’s enclosure in which air could enter and/or fire could escape — must be limited to prevent flame propagation to the outside. Thus, even if a device is sparking and/or has ignited on the inside, flame will not escape or propagate outside of the component.

Annex 101.DVL defines this opening as the effective diameter — which is the equivalent diameter of the opening of relays and similar components — via the following calculation:

d_eff = 4 × (A/S)

• d_eff is the effective diameter in mm
• A is the cross-sectional area of the opening in mm²
• S is the length of the perimeter of the opening in mm

Thus, relays and similar electrical components are not considered as potential ignition sources if the effective diameter of all openings complies with the following calculation:

d_eff < 22.3 × S_u^-1.09 (in mm) ≥ 7 mm

• d_eff is the effective diameter in mm
• S_u is the burning velocity in cm/s

There are certification exceptions for certain relays and/or switching devices. Per UL 60335-2-89, 2^nd edition, Clause 22.111.1DV, those that are not considered ignition sources are deemed inherently compliant to the standard and do not need to be tested for compliance with the UL standard. To qualify for this exception, these devices must meet the following criteria:

• Capable of 100,000 cycles, per Clause 24, and

• The switched electrical load (L_e) in kVA is less than or equal to:
• L_e = 5 × (6.7/S_u)⁴ when breaking all phases (~66 kVA)
• L_e = 2.5 × (6.7/S_u)⁴ when breaking two legs of a three-phase load, or when breaking one or two legs of a single-phase load

where

• L_e is the switched inductive electrical load in kilovolt-amperes (kVA)
• S_u is the burning velocity of a refrigerant in centimeters per second (cm/s)

See UL 60335-2-89, 2^nd edition, Clause 22.111.1DV for more information on compliance measurement and testing.

For electrical enclosures and/or system level certification, UL 60335-2-89, 2^nd edition, Annex 101.DVM provides a comprehensive range of testing requirements to certify that they comply with its flame-arrest enclosure verification standard. A flame-arrest enclosure is defined as a “device or assembly enclosing components with electrical contacts that are made and broken, or similar devices which can become a source of ignition.”

A qualifying enclosure must be able to withstand the internal ignition of leaked A2L refrigerant vapor, without suffering damage and transmitting flame to an external concentration of the same refrigerant. Note: qualified individual electrical components contained within a flame-arrest enclosure are not to be considered as sources of ignition.

If all openings in the flame-arrest enclosure comply with the Annex 101.DVM standard, the enclosure is considered compliant.

Regardless of all other testing and certification measures, the surface temperature limits of affected electrical devices must also be factored into the A2L safety equation. Per Clause 22.114 in the UL 60335-2-89, 2^nd edition standard, surface temperatures cannot exceed those defined in Table 102.DV (see Table 1).

Refrigeration Potential

A2L refrigerants have vast potential in the commercial refrigeration sector, delivering a unique combination of lower GWP, high performance, and energy efficiency. By using equipment and components optimized and certified for A2L refrigerants, specifying engineers and contractors can help their retail customers safely transition to this emerging refrigerant.

Copeland is committed to developing safe, A2L-optimized compression, controls, and electrical componentry to give specifying engineers and contractors a range of system options from which to support their customers’ next-gen equipment strategies. We have the application and engineering expertise — and flammable refrigerant testing facilities — to help maximize equipment safety using the next generation of low-GWP refrigerants.

OPTIMIZED FOR A2L: Copeland is committed to developing safe, A2L-optimized compression, controls, and electrical componentry. (Courtesy of Copeland)