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ul 9540
Scott ChambersSep 14, 20236 min read

What You Need To Know About UL 9540

Imagine that you’ve created a new electronic product.

Your product is amazing, and you would love to show it to the world. But what happens when you turn it on? The battery instantly catches on fire, leading to a whole world of unhappy customers and recalls, worsening your reputation, and inviting potential lawsuits.

Many products are tested for reliability before coming to market, and when it comes to electronic goods, the best way to certify them is through a UL certification. 

Over the last three decades, Strouse has worked to ensure accuracy in the parts we build. UL certification requires that your product meets industry safety standards, for example, the UL 9540 energy storage standards.

 In this post, we’ll cover:

  • The difference between UL Listed and UL Recognized
  • The difference between UL 9540 and 9540A
  • Requirements for UL 9540
  • How to get UL certified
  • What you should know after getting approved

 If you have a product that could require electronic safety testing, reading this article will prepare you for that project phase. 

What Is The Difference Between UL Recognized and UL Listed?

At first, it can be challenging to differentiate UL Recognized from UL Listed. Fortunately, with some explanation, it’s easy to distinguish them.

UL Recognition is more production-focused, centering around your product's machinery and different working parts. With Recognition, UL has ensured that your equipment is properly housed but might need additional installation precautions.

UL Listed is a stand-alone product, meaning the whole product was tested rather than just its components. 

In short, UL Recognition checks product components for industry standards, while UL Listed checks the whole product.


Whether you seek UL Recognized or Listed ultimately depends on your needs. For instance, you’d likely want a UL Recognized certification if the various components of your product had specific industry regulations in place. 

Tips To Succeed in Your Adhesive Design Phase 

UL Listed Requirements

UL-listed products have undergone many requirements, most of which are based on UL’s published Standards for safety. Yet, products are evaluated with additional needs in cases such as:

  • Functional safety
  • Energy efficiency
  • Use in security
  • Use in gas-fired equipment and marine environments

In addition, the environmental and safety codes differ from state to state, so you should ensure you check with UL to remain compliant.

The last consideration is UL’s marketing. When displaying the certification, an appropriate version of the UL listed mark is typically enough as long as your product shows the complete UL mark. 

UL 9540 vs. UL 9540a — What’s the difference?

The difference between UL 9540 and UL 9540a is that the former is a group of standards for energy storage systems to follow, and the other is a specific test intended to gauge thermal runaway. 


UL 9540 is a safety standard for an energy storage system (ESS) and equipment intended for connection to a local utility grid or standalone application. It designates vital issues associated with ESS, including: 

  • Safety of the battery system
  • Functional safety
  • Fire detection & suppression
  • Containment
  • Environmental performance
  • —and more!


UL 9540A, on the other hand, is a test method for evaluating thermal runaway propagation for battery energy storage systems. This is very useful for engineers and developers to verify the effectiveness of the product’s protection against key issues like fire. 

The UL 9540A test does NOT give you the certificate directly. Instead, it provides data for manufacturers to see if their product meets the regulations. 

The UL9540A Test Hierarchy

UL 9540a tests are performed to determine how the electronic components might act in a worst-case scenario. There are four stages in the UL9540A test method:


At this level, UL looks at whether a cell can exhibit thermal runaway. It also checks its characteristics and flammability.


In this stage, the main goal is determining if thermal runaway propagates with the module. They will also find out the heat release and gas composition.


Now, they will look at the whole unit and see the following. Firstly, they find out how quickly fire spreads. Then, they will look for its heat and gas release rates and other hazards.


Lastly, they do an installation test. This is an optional test, but its goal is to determine the effectiveness of the product’s fire protection.

Requirements for UL 9540

Before getting a UL certification, you must ensure your product meets the requirements! For UL 9540, your device shouldn’t exceed the maximum energy capacity: 

  • For outdoor wall-mounted electrochemical ESS, not over 20kWh (72 MJ)
  • For residential use, electrochemical ESS, not over 20kWh (72 MJ)
  • For non-residential use, electrochemical ESS not over 50kWh (180 MJ)

You should also check that the product’s polymeric materials comply with the requirements outlined in UL 746C. The only exceptions are electronic systems intended for outdoor installation and electrochemical ESSes. These need to employ an enclosure of non-combustible materials. 

Lastly, before you get a product certified, ensure you’ve got some cash in hand. Getting your product approved usually costs between $5,000 to $15,000.

How To Get Your UL Certification

So, you’re wondering how to get your product UL-certified. Fortunately, the process is relatively simple.

First, go to UL’s website and navigate to the “Contact Us” page. You’ll find all the relevant information and forms to submit your product sample for UL testing.

Next, you’ll send in your product sample. Once UL has received your prototype, they will start taking tests and ensuring that your product fulfills OSHA and ANSI standards.  

As soon as the tests are completed, they’ll decide if the product complies with the requirements and standards. Then UL charges a fee for the administration of the tests.

Once UL has verified that your product is safe and fulfills OSHA and ANSI standards, they will issue you a certificate. Then, you can add the UL logo to all manufactured products. 

This whole process usually takes around six months but could also take multiple years. It all depends on how complex your product is and if the prototype is technically compliant with all applicable UL standards.

After Getting Certified

Congratulations! Your product got accepted for UL certification. Yet, you should know a few more things going forward. 


After getting your UL certification, you’ll be required to let them inspect your product regularly. This is to ensure that your product maintains UL’s standards. When UL spots that your product is non-compliant, you will be given a variation notice, and you’ll have to resolve any issues as fast as possible.


Now, it’s harder to do redesigns. You’ll have to pick from two options when modifying a certified product. Either choose a material approved by UL or send your revised product for another patch of tests.

Final Words And How We Can Help

There are many steps to getting a UL certification. However, you’ll not only get confirmation that your product is safe and reliable, but also your clients will trust you more because of the UL logo.  

But if your product needs to be optimized before you submit it, it can take you way longer than anticipated. This will not only delay your product launch but also increase your costs. 

In the worst-case scenario, you might even ditch the whole project, causing your effort and money to go to waste. 

Schedule a Flexible Materials Consultation

Don’t risk delaying your project because of confusion over certifications or an overly complicated design. Instead, if you want a second opinion to have a look at your flexible material product, talk to a converter or get an evaluation on your part drawing.



Originally published: May 25, 2021


Scott Chambers

As the VP of Sales and Marketing for Strouse, Scott oversees Strouse's Go-To-Market Strategy. Scott has a BS in Business Management from Coastal Carolina, a JD from the University of Baltimore School of Law, and an MBA from Indiana University.