UL 9540 is the standard for safety for Energy Storage Systems (ESS) and Equipment. UL 9540 can cover multiple types of systems from electrochemical, chemical, mechanical, or thermal.

UL 9540 is also a system listing meaning that individual parts and pieces of equipment are not considered to be UL 9540 listed on their own.

To obtain UL 9540, the energy storage system must be evaluated and tested for compliance with the standard.

• UL 9540A is a test method for compliance. It is performed on technologies to understand thermal properties and evaluate thermal runaway fire propagation of a product or energy storage system.
• UL 9540 is a safety standard and system listing for ESS and equipment.

UL 9540 references UL 9540A and, to meet some portions of UL 9540, an ESS must have acceptable UL 9540A test results.

If a product has acceptable UL 9540A test results, that does not automatically mean that it will meet the requirements as a system for UL 9540 listing.

Having UL 9540A-acceptable results for an ESS larger than 50kWh allows all battery racks or DC technology cabinets to be side by side, taking up less footprint.

The DC technology in question must have acceptable UL 9540A test results and those full test reports must be provided to the Engineer of Record (EOR) and Authorities Having Jurisdiction (AHJs).

NFPA 855 is the standard for installation of a Stationary Energy Storage System. 

In general, NFPA 855 states that, “any energy storage device, especially lithium-ion, over 20kWh shall be certified to UL 9540 and tested to UL 9540A with acceptable results.”  

Technology Test (UL 9540A) + ESS System Listing (UL 9540) = National Standard for the Installation of Stationary Energy Storage Systems (NFPA 855) 

UL and the NFPA 855 consider a UPS system to be an ESS and, therefore, are subject to UL 9540 requirements.  

NFPA (the guiding fire safety standard), UL 9540 (the system safety listing), and UL 9540A (the standardized test method for thermal runaway fire propagation) create the trifecta of safety. The safest energy storage systems obtain all three of these and stay up to date on codes and standards.  

As standards, codes, and listings are adopted, and new revisions are published, local AHJs and regional fire codes can be slow to adopt the latest revisions.  

In some areas of the country, NFPA 855 is not yet required and local AHJs have the authority to accept or not accept the latest standards and codes. This makes standard and code compliance for fire safety somewhat complicated throughout the United States.  

No, many different types of energy storage systems are required to meet UL 9540 standards to be NFPA 855 compliant – and those requirements vary depending on what kind of system it is. A UL 9540 compliant system could be a bi-directional inverter with VRLA batteries, or a UPS system with super capacitors. 

VRLA and lead acid batteries are included under certain stipulations in UL 9540. Typically, they are exempt from having to meet the stringent fire safety requirements that other DC technologies do.  

In NFPA 855, there are some requirements but those are implemented at the discretion of the AHJ.  

Per UL 9540 Third Edition: 1.5: “Systems using lead acid or Ni-cad batteries that fall within the scope of UL 1778/CSA C22.2 No 107.3 and only serve an uninterruptible power system (UPS) application are outside the scope of this Standard.” 

What this means is if VRLA batteries are used with a UL 1778 UPS system and application, they are exempt from the UL9540 Standard.

1. DC Technology Compliance to UL 9540A: The DC technology needs to have been tested, with approved results to UL 9540A (if applicable), and UL listed to appropriate standards and listings. For example, many batteries and DC technologies currently require UL1973 listing and compliance.  

2. Test the Full System: The UPS and DC technology must be tested, validated, and verified together as an energy storage system. For a UPS system to receive UL 9540 listing, it requires testing, validation, and verification by UL or a UL nationally recognized and approved testing agency.  

3. UL 9540 Listing & Certification: Once the system is successfully tested, verified, and validated per the evaluation, the system will be listed on the UL Product IQ page as being UL 9540 system listed and certified.  

In the UL or ETL database, the certification should be categorized under the “FTBW” category code for Energy Storage Systems. Once it is certified, the process becomes more project specific.  

4. Listing & Labeling at Installation Site: The final testing and evaluation for UL 9540 listing and labeling happens at the site of installation. This location could be at the integrator for a containerized solution or at the end customer’s site.  

Mitsubishi Electric can help with coordination of the UL inspector, list the site as a temporary manufacturing location, and help apply UL 9540 labels to the system.  

All parties will need to coordinate and make sure the necessary documentation is provided to UL and that the process is successful.