Understanding UL, When is it Applicable?

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There are a lot of questions asked about UL Ratings when it comes to components and fully designed products. This post will cover some of the important information about UL such as what components typically have UL Recognized Certification, what products tend to have UL Listed Certification, and talk about some misconceptions about UL.

Before reading this post I suggest you take a look at a related topic comparing UL Listed versus UL Recognized: The Difference Between "UL Listed" and "UL Recognized"

Factors That Determine if UL Testing Should be Considered

There are three factors considered by a manufacturer that is considering UL Listing or UL Recognized certification. The first is the application and its environment. If the application is going to be used in a harsh environment, it is generally recommended that UL Listed product is used since they are tested as whole units. The second is additional planning and protection when selecting components. UL Recognized components may need to be further protected from dust, liquid, and impact. If you plan on having a system that needs components to be protected but don’t necessarily need the entire device to conform to UL Standards, then UL Recognized parts may be sufficient enough. Last is the amount of standards required in a design. If there are a lot of standards that coincide with UL standards, it may be best to get UL Listed products that fit your needs rather than individual components that are UL Recognized.

Components That May Have UL Recognized Certification

Here is an incomplete list of common components that could have UL Recognized documentation:

  • Single and Multi-Conductor Cable: Certain jacket materials tend to be flammable, UL 94 often applies in this case.
  • Class-X and Class-Y Saftey Capacitors: These types of capacitors have such a high voltage rating that fire danger or electrical shock (sparking) is possible if used incorrectly or fail.
  • Some Batteries: batteries are often found in household electronics, so UL Recognition may apply.
  • Heat Shrink or Other Cable Protection
  • Fuses
  • Circuit Breakers
  • Anything That is Specifically Designed for Circuit Protection: some examples may include gas discharge tubes, inrush current limiters, surge suppression IC's, and TVS components.
  • Certain Power Management IC's
The general rule is that anything built for high standards or providing power typically tend to have UL Recognized Certification.

Fully Designed Product That May Have UL Listed Certification

Here are some products that typically have UL Listed documentation:

  • Any product that has an AC Plug, these typically have UL Listings;
    • Examples:
    • Gateways and Routers
    • Soldering Irons and Soldering Stations
    • Wall Mounted Power Supplies and Desktop Supplies
    • Printers
  • Industrial Application Products
    • PLCs
    • Circuit Breakers: some breakers may be considered full products
    • VFDs
    • Industrial Power Supplies
  • Some evalutation boards and specialized boards may have UL Listings or UL Recognized documents, it's best to check the datasheets if unsure.

If any component or product does not fit what I’ve discussed, then it probably won’t have UL documentation and most likely never will. It turns out that some items don’t even have specifications that would be applicable to UL standards. Some product is never going to be safe enough to be UL tested by design.

Common Misconceptions or Less Known Facts About UL

  • There is no such thing as a general UL Approval, this is something said everywhere but does not reflect UL's standards. A manufacturer is responsible for getting things certified.
  • Not every part or product is tested by UL, some manufacturers are given authority to test their own products and have UL follow up on a regular basis to make sure guidelines are being met.
  • All products don't necessarily have to be tested. A product may contain several components that are never UL tested because it's not required. However, one important note, most complete products are UL Listed due to National Electric Code stating that UL Listed products must be used when available.
  • UL Testing is completely voluntary per manufacturer.
  • If a part or component is not UL tested, it does not mean it will burst into flames or be considered unsafe. They simply haven't been tested to meet UL standards.
  • It costs a lot more to have a product UL Listed than have components UL Recognized.

Here is an excellent resource where I got a lot of information from. This article was written by one of our suppliers, CUI: What is the Difference Between UL Listed and UL Recognized? | CUI Inc Remember to check the datasheet for what you are looking at if you think there should be UL documentation, that is where it will most likely be mentioned.

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