2025-01-13
Flame testing and glow wire testing are two approaches to determining the flame-retardant performance of materials like various plastics and the electronic devices that incorporate those materials. Flame testing are defined in IEC 60695-2-2, while glow wire testing is defined in IEC 60335 and IEC 60695. UL94 is another material burning test and can be either a horizontal burn (UL94 HB) or a vertical burn (UL94 V) test. This FAQ looks at glow wire testing, needle flame, and UL94 burning to test and compares the performance and testing requirements for the various approaches.
These tests are designed to protect against fault conditions like excessive leakage currents, poor (high resistance) electrical connections, or outright short circuits that can cause overheating resulting in fire. Since connectors can be subject to all these fault conditions, they are among the components most often required to pass these tests. The glow wire and needle flame tests are sometimes used in combination. The glow wire test is administered first, and if the part fails, the extent of the burning hazard can be further assessed with the needle flame test.
Glow wire testing：
Glow wire testing uses a heating element at a pre-determined temperature, depending on the specific test. The heating element is called the ‘glow wire.’ In addition, a fiber cloth called tissue paper is below the material or device being tested. After reaching the required temperature, the glow wire is pressed against the test specimen using a force of 1 N for 30 seconds (Figure 1). If the specimen catches fire, the ignition start time, duration, flame height, and, if the material drips, notes regarding if the fibers of the tissue paper are charred or ignited are recorded. The test is repeated three times using new specimens, changing the mounting orientation so each unique surface, like front or back, top or bottom, and left or right side, is tested. Test samples for glow wire testing should be at least 60 mm long and at least 60 mm wide with a thickness of 0.75 ±0.1 mm, 1.5 ±0.1 mm, or 3.0 ±0.2 mm.
Glow wire testing complies with IEC 60335-1 for household and similar electrical appliances for resistance to heat and fire and includes a glow wire ignition temperature (GWIT) of at least 775 C° as defined in IEC 60695-2-13 and a glow wire flammability index (GWFI) above 850 C° defined in IEC 60695-2-12. Glow wire performance requirements are defined in IEC 60335. Glow wire testing can be performed on raw materials and end products. Compliance is defined differently for the two cases.
Flame testing：
The IEC needle flame and UL 94 tests take different approaches to certify material and product safety. The needle flame test uses a burner with a 0.9 mm tip and butane gas at an angle of 45°. It’s designed to evaluate the hazard of small flames caused by fault conditions. Needle flame tests are evaluated according to the requirements of the specific product standard. For product standards that don’t specify needle flame testing, the generic requirements are:
UL 94 is a material burning test and can be a UL94 HB test or a UL94 V test (Figure 3). In both tests, an open flame is applied to the specimen for a set amount of time (see Table 1 below). UL 94 has been harmonized with IEC 60707, 60695-11-10, 60695-11-20, and ISO 9772 and 9773.
A material having a thickness between 3 and 13 mm will be classified as a UL94 HB (slow burning) material if it has a burn rate of 40 mm per minute or less. For material with a thickness of less than 3 mm, the burning rate can’t exceed 75 mm per minute. The material will also be rated as HB if it stops burning before the 100 mm mark, regardless of thickness. Vertical burn ratings are more nuanced (Table 1). The 5VA or 5VB ratings require testing with a flame ignition source about five times more severe than that used in the V-0, V-1, V-2, and HB. And 5VA and 5VB specimens may not drip any flaming particles.
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