Fire can be a devastating event for any kind of business, so it’s essential to take the right steps to protect your devices and your building against fire-related hazards. Polycase provides flame ratings associated with the material on all of our plastic enclosures for electronics so customers know their devices are safe inside our enclosures.We rate our enclosures’ flame resistance using the UL 94 flame rating system, which is the most commonly used industry standard for flame-rated enclosures. Here, we’ll discuss the basics of UL 94 flame ratings and how to understand them as they relate to electrical enclosures.
fire inside electrical fuse box

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Understanding UL 94 Flame Ratings

The UL 94 flame rating is a safety standard widely popular in the world of polymer plastics materials. Underwriters Laboratories (UL), the leading independent safety testing organization who first developed the standard, maintains the standard and administers testing today. The tests conducted measure flammability characteristics of the material and determine the plastic’s propensity to either extinguish or spread a flame once ignited. Factors evaluated include:
  • Whether the material ignites when exposed to a flame ignition source
  • Whether the flame spreads after flame application, and how quickly
  • Whether the material releases flaming particles as it burns
There are six classifications on the UL 94 flammability ratings scale that relate specifically to plastic enclosures (5VA, 5VB, V-0, V-1, V-2 and H-B). Enclosures that receive UL 94 5VA or UL 94 5VB ratings have been tested using a flame source five times more intense than what’s used in the V-0, V-1, V-2 and H-B test and, thus, UL 94 5VA enclosures are considered the most flame retardant.

UL 94 Flammability Standard Ratings:

5VADoes not ignite under flame, does not have a burn-through hole * Most flame-retardant UL 94 rating5VBDoes not ignite under flame, may have a burn-through holeV-0Self-extinguishing within 10 seconds, no flaming dripsV-1Self-extinguishing within 60 seconds, no flaming dripsV-2Self-extinguishing within 60 seconds, flaming drips may occurH-BSlow burn rate, takes more than three minutes to burn four inches *Least flame-retardant UL 94 ratingNote: Other UL 94 ratings exist for certain types of specialized materials, such as the HBF ratings for foam materials, but these are the ratings most relevant to electrical enclosures.Each of these classifications denotes a specific testing method used on the enclosure’s material. For example, each rating with a “V” includes a vertical burning test, while “H-B” means “horizontal burn” and refers to (as you might guess) the horizontal burning test. Both the horizontal and vertical tests provide key information about how a material will react to flame application. Note that, by necessity, these flammability tests are performed in laboratory conditions on test specimens. Although UL designs its testing methods to be extremely rigorous, the tests may not always perfectly reflect the flammability of plastic materials under actual fire conditions, which are (by nature) highly unpredictable.The UL 94 standard is designed specifically to measure the flammability of plastics, so it does not apply to metal enclosures. The materials from which we produce metal enclosures, such as steel and aluminum, are naturally non-combustible. Our metallic enclosure options thus can also be a good choice for applications that require heat resistance.

Why the UL 94 Standard Is Important

Plastic enclosures are popular for many reasons. They’re versatile, extremely tough and available with all kinds of features and customizations. However, some applications, especially in hazardous environments and industrial settings, require the use of flame-retardant plastic enclosures.That’s why using UL 94 rated enclosures is often an important part of an organization’s fire safety practices. Their importance is twofold: For one, a flame-retardant enclosure helps prevent the further spread of fire, including (for some UL 94 ratings) preventing the flaming drips of plastic that can be especially dangerous. In addition, a flame-retardant enclosure helps maintain the integrity of critical systems during a fire. Many businesses need to know their most important systems, such as safety systems or data backups, will have the best chance possible of surviving a fire event. Thus, UL 94 ratings will often be a key part of material selection and evaluating suitability when specifying enclosures for your most important applications.Polycase ZH-080604 Enclosure

Polycase ZH-080604 Enclosure

UL 94 V-0 , UL 746C 5VA Rated

Does Polycase Offer UL 94 Rated Enclosures?

Yes, all of our plastic enclosures use material that has undergone UL 94 flame rating testing! We also carry enclosures tested under the related UL 746C standard, a standard designed specifically for the control of electrical fires.These ratings can be found on the “ratings” tab of each product’s page. Questions or comments? Reach out to Polycase’s enclosure professionals to get the information you need on our enclosure selection. We’ll be happy to tell you about the UL ratings of our enclosures or any other performance specs.
In UL Rated Plastic Enclosures