We are often asked about our flammability ratings and what they mean. Quite simply, they allow the designer to understand how the plastic material will act when exposed to fire and how it impacts that fire. A key point is that the testing is done on a sample of the material, not on the final enclosure. Further, it does not deal with how the box will protect the components but more how the material will react when exposed to a flame. It assists in understanding how will the enclosure will protect against the fire or, potentially, if it will contribute to it.
Here are the ratings that are most often developed for the materials that are used to make plastic electronic enclosures:
From lowest (least flame-retardant) to highest (most flame-retardant):
- HB: slow burning on a horizontal specimen; burning rate < 76 mm/min for thickness < 3 mm or burning stops before 100 mm
- V-2: burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
- V-1: burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
- V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
- 5VB: burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may develop a hole.
- 5VA: burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may not develop a hole.
These are all tested to specifications that are developed by UL dealing with the thickness of the sample, the flame size and duration of flame application. For example, HB has no requirements about what happens to the burning material where V-2 can allow dripping melted particles that can increase the fire and V-0 allows drips that are not inflamed and 5VA allows no drips or holes in the material.
As always, there is a cost/benefit ratio to having a material with greater fire protection for your plastic electronic enclosures. It is easy to choose the highest level of protection but depending on the application and location, the designer could be wasting a great deal of money over the life of the project.
If you have more questions, don’t hesitate to contact Bud to insure that your choice of enclosure provides the proper level of protection for your application.