What is Glow Wire Testing?
Historically a number of methods have been developed to evaluate material flammability and fire resistance.
These include both direct flame and indirect flame testing methods. An example of the direct flame method is defined in the UL 94 specification. This long accepted test method involves applying a flame directly to a vertically or horizontally mounted specimen under controlled conditions. On the other hand, the indirect flame method features a non-flaming heat source applied to a sample. Glow wire testing is an example of the indirect flame method. Test results from applying these methods provide a way to compare the materials’ tendency to resist ignition, self-extinguish flames (should ignition occur), and to not propagate fire via dripping. To better understand the differences between the direct method and the indirect method, refer to Figure 2.
The International Electrical Commission (IEC) established the glow-wire testing method in 2001 because existing test methods did not cover all ignition sources. Specifically, the glow wire test is used to simulate heating effects that may arise in malfunctioning electrical equipment caused by an overloaded connection or component that is overheating.
Test Methodology：
Glow wire requirements for home appliances are specified in IEC 60335-1. However, the actual glow wire test methodology is covered in the IEC 60695-2 series of specifications.
Glow wire testing is performed by heating an element to a pre-determined temperature. The heated element is referred to as the glow wire. See figure 3 for an example of the heated element used for glow wire testing.
The sample to be tested is fixture in place and tissue paper is positioned directly below the sample. After reaching the pre-determined temperature, the element is then pressed into a sample material under a set force of 1N for 30 seconds. If ignition occurs, recordings are made to note the duration, flame height, and if drips of the material ignite the tissue paper.
Glow wire testing can be performed on both end products and raw material test plates. The terminology used to define compliance in each case is slightly different.
1. GWT stands for Glow Wire Test (IEC 60695-2-11). GWT is used when glow wire testing is
performed on an end product. The results of this test will be either PASS or FAIL at a given
temperature. Passing the test requires that the sample does not ignite or self-extinguishes within 30 seconds after removal of the heated element. Also, the sample may not ignite the tissue paper if drips occur.
2. GWFI stands for Glow Wire Flammability Index (IEC 60695-2-12). This is a property associated with raw material used in the end product. This property is determined by conducting the glow wire test on a test plate of a raw material of a given thickness. The Glow Wire Flammability Index (GWFI) is the highest temperature at which the material does not ignite or self-extinguishes within 30 seconds after removal of the heated element.
3. GWIT stands for Glow Wire Ignition Temperature (IEC 60695-2-13). This is a property
associated with raw material used in the end product. This property is determined by conducting the glow wire test on a test plate of a raw material of a given thickness. The Glow Wire Ignition Temperature (GWIT) is the lowest temperature at which the material ignites and burns for longer than 5 seconds while the heated element is in contact with the test plate.
Knowledge of the three terms is essential to understand how glow wire testing is applied under the overall safety standard IEC 60335-1.