Hello Scott, There are two different approaches to testing materials for flammability ratings. UL 94 determines what happens when plastics are ignited. It determines how material burn and whether they self- extinguish. These tests are based on the assumption that the material will ignite and then see how the material burns. The tests look at the rate of flame spread, dripping particles and other factors.
The glow wire test takes a different approach. It determines how easy or hard it is to ignite a material in the first place. A material may burn easily, but if it’s extremely hard to ignite, the rate at which it burns might not be an issue. Magnesium is used as a light-weight material for IT products, engine blocks and high-performance automobile wheels. Once it is ignited, it burns rapidly and releases a lot of energy. However, it’s very hard to ignite solid metallic magnesium in the first place. In summary, some standards are concerned with whether or not a material ignites easily and then don’t test how well they burn after they are ignited. Materials that don’t ignite easily are accepted. Other standards only test how materials burn. If materials don’t burn quickly and resist flame spread, the standard doesn’t test how easily they ignite. They address the same problem through different approaches. The different temperatures for glow wire tests represent different ignition sources. One is a medium energy source and the other a higher energy source. Materials that resist the higher temperature are considered harder to ignite. Ted Eckert Microsoft Corporation The opinions expressed are my own and do not necessarily reflect those of my employer. From: Scott Xe <[email protected]> Sent: Wednesday, November 21, 2018 8:54 AM To: [email protected] Subject: [PSES] Glow wire tests I notice in safety test standards that the plastic enclosure is required to pass glow wire test. What does this test for? There are commonly two conditions: 550 or 750 degC. What are the differences and what does each represent its capabilities? I am new to this requirement and appreciate your decent explanation. Thanks and regards, Scott - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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