Glow wire test
| Type | Fire safety test |
|---|
The glow-wire test (GWT) is a standardized physical-thermal test method used to evaluate the fire hazard of solid electrical insulating materials and other solid combustible materials. It simulates the thermal stress that may occur in electrical equipment due to an overloaded connection or a glowing heating element under fault conditions.
The test is widely used in product safety certification for household appliances, electronic devices, connectors, switches, and plastic components. It is primarily defined in the International Electrotechnical Commission (IEC) 60695 series of standards.
Purpose
The glow-wire test determines a material’s resistance to ignition, its self-extinguishing capability after exposure to a high-temperature wire, and whether flaming droplets may spread fire to surrounding materials. It is particularly important for assessing the fire safety of unattended electrical appliances.
Test apparatus and procedure
The test employs a nickel-chromium resistance wire (the glow-wire) heated by electric current to a specified temperature, typically ranging from 550 °C to 960 °C. The heated wire is pressed vertically against the surface of the test specimen with a force of 1.0 N for 30 seconds and then removed. The burning behaviour of the specimen is observed for up to 30 seconds after withdrawal of the glow-wire.
A layer of tissue paper is placed 200 mm below the specimen to detect ignition caused by flaming droplets or falling material.
Key performance indices
- Glow-Wire Flammability Index (GWFI) (IEC 60695-2-12): the highest temperature at which the material meets the pass criteria in three consecutive tests — flame or glowing combustion extinguishes within 30 seconds after removal of the glow-wire, and the underlying tissue paper is not ignited.
- Glow-Wire Ignition Temperature (GWIT) (IEC 60695-2-13): the temperature at which the material ignites and sustains combustion.
Test conditions
- Specimen dimensions: minimum 60 mm × 60 mm, with preferred thicknesses of 0.75 mm, 1.5 mm or 3.0 mm.
- Conditioning: at least 48 hours at (23 ± 2) °C and (40–60)% relative humidity.
- Multiple fresh specimens are tested at incrementally increasing temperatures.
Relevant standards
- IEC 60695-2-10 — Glow-wire apparatus and common test procedure
- IEC 60695-2-11 — Glow-wire flammability test method for end-products (GWEPT)
- IEC 60695-2-12 — Glow-wire flammability index (GWFI) test method for materials
- IEC 60695-2-13 — Glow-wire ignition temperature (GWIT) test method for materials
Corresponding national adoptions exist, such as the GB/T 5169 series in China and UL 746A in the United States.
Applications
The glow-wire test is required by many end-product safety standards, including:
- IEC 60335-1 (Household and similar electrical appliances)
- IEC 60598 (Luminaires)
- IEC 60950 / IEC 62368 (Information technology equipment)
For unattended appliances, materials often need to achieve GWFI ≥ 850 °C or GWIT ≥ 775 °C.
See also
References
External links
- IEC 60695-2-12:2021 — Glow-wire flammability index (GWFI)
- IEC 60695-2-13:2021 — Glow-wire ignition temperature (GWIT)
- IEC 60695-2-11:2021 — Glow-wire flammability test method for end products
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