Glow wire testing is a critical fire-safety evaluation that assesses how non-metallic materials and components in household appliances respond to simulated thermal stress from glowing wires or overheated connections. Governed by the IEC 60695-2 series and corresponding GB/T 5169 national standards, this test verifies that plastic housings, insulating parts, and electrical components can resist ignition and prevent the spread of fire. This article explains the technical principles, test methods, applicable standards, and compliance requirements for glow wire testing of household appliances.
Technical Overview
Glow wire testing (also known as the glow-wire test) is a fire hazard assessment method used to evaluate the flammability characteristics of electrically insulating materials and finished components. The test simulates thermal stress caused by abnormally glowing components, such as overloaded resistors, poor electrical connections, or deteriorated contacts, which may occur during real-world appliance malfunctions. The method is defined in the IEC 60695-2 series of standards, which has been adopted internationally as EN 60695-2 and in China as the GB/T 5169.10 through GB/T 5169.13 standards.
The test apparatus consists of a nickel-chromium (NiCr) resistance heating wire, approximately 4 mm in diameter, bent into a standardized loop shape. The wire is heated electrically to a specified temperature, typically between 550°C and 960°C, and its tip temperature is verified using a fine-wire mineral-insulated thermocouple. The heated tip is then pressed against the surface of the test specimen with a defined force for a fixed duration, and the ignition behavior, flame duration, and dripping of burning material are observed and recorded.
For household appliances specifically, the parent safety standards IEC 60335-1 (internationally) and GB 4706.1 (in China) define which parts must undergo glow wire testing, at which temperatures, and under which pass criteria. These requirements depend on factors such as the appliance power rating, whether the appliance operates unattended, and the proximity of parts to live electrical connections. Manufacturers routinely engage accredited third-party laboratories to perform these tests for product certification and market access.
Testing Samples
Material Test Plates
Flat specimens of polymeric materials, typically of preferred dimensions, are tested to determine the fundamental glow-wire performance of the compound itself. These plates, usually of standardized thickness, are used to establish the glow-wire flammability index (GWFI) and the glow-wire ignition temperature (GWIT) of a material, which are valuable for material pre-selection during product design. Materials commonly evaluated include ABS, PC, PBT, PA (nylon), PP, and various flame-retardant grades.
Finished Components and Parts
Complete molded parts removed from appliances are tested as end products. These include enclosures, covers, switch actuators, terminal blocks, connectors, fan blades, circuit board supports, and internal barriers. Testing finished parts is essential because geometry, wall thickness, proximity to other materials, and contamination can all influence real fire behavior compared with flat material coupons.
Complete Assemblies
In certain cases, sub-assemblies such as switch assemblies, power entry modules, or control panels are tested in their installed configuration to evaluate how the interaction of multiple parts affects ignition and flame propagation within the appliance.
Testing Items
The glow wire test family comprises several distinct evaluations, each defined by a specific standard and pass criterion:
- Glow-wire flammability test on end products (IEC 60695-2-11 / GB/T 5169.11): The heated glow wire is applied to a finished part mounted in its normal operating position, and flaming behavior is assessed.
- Glow-wire flammability index, GWFI (IEC 60695-2-12 / GB/T 5169.12): Determined on material test plates; the GWFI is the highest temperature at which the material meets the defined criteria in three consecutive tests.
- Glow-wire ignition temperature, GWIT (IEC 60695-2-13 / GB/T 5169.13): The temperature 25 K (or 30 K in specific cases) above the highest temperature at which ignition of the material does not occur during the test, determined on material plates.
Common test temperature levels include 550°C, 650°C, 750°C, 850°C, and 960°C. The temperature required for a given part depends on its function, location, and the applicable clause of the product safety standard.
Testing Methods
The glow wire test procedure follows a rigorous, standardized sequence to ensure repeatability and comparability of results:
- Temperature stabilization: The glow wire is heated to the specified temperature and allowed to stabilize, with the tip temperature verified by the embedded thermocouple. Verification against standardized silver foil melting confirmation is performed periodically.
- Specimen mounting: The sample is secured on the carriage so that the glow wire tip contacts a flat, smooth, and preferably vertical or horizontal surface in the area of worst-case exposure.
- Application of the glow wire: The heated tip is pressed against the specimen with a contact force of approximately 1 N for a duration of 30 seconds, with penetration of the tip limited to a maximum depth of about 7 mm.
- Observation and recording: Test engineers record whether the specimen ignites, the duration of any flaming or glowing after removal of the glow wire, whether burning drops fall, and whether a layer of wrapping tissue paper placed 200 mm below the specimen is ignited.
- Evaluation of results: For most end-product requirements, the part passes if any flame or glowing extinguishes within 30 seconds after the glow wire is removed and the tissue paper placed below does not ignite.
For GWFI determination, a material passes at a given temperature if there is no flame or glowing, or if flames extinguish within 30 seconds after removal and the tissue paper does not ignite. For GWIT determination, ignition is defined as flaming or glowing persisting longer than a specified time after removal of the glow wire. Testing is typically repeated on multiple specimens at each temperature to confirm consistent results, and all testing is conducted in a draft-free enclosure under controlled ambient conditions.
Applications
Glow wire testing applies to virtually every category of household and similar electrical appliances, because fire safety is a universal requirement of the IEC 60335-1 and GB 4706.1 product standards. Typical product categories include:
- Refrigerators, freezers, and air conditioners, which operate unattended and therefore face elevated temperature requirements for certain parts.
- Washing machines, dishwashers, and clothes dryers.
- Microwave ovens, electric ovens, rice cookers, electric kettles, toasters, and other heating appliances.
- Vacuum cleaners, fans, hair dryers, and personal care appliances.
- Component-level products such as switches, plugs, socket-outlets, terminal blocks, and printed circuit board materials.
The test results support mandatory certification schemes, including CCC certification for appliances sold in China, CE marking under European harmonized standards, and voluntary safety approvals in other markets. Beyond regulatory compliance, glow wire data guide material selection, flame-retardant formulation development, supplier qualification, and internal design reviews. Manufacturers frequently partner with accredited third-party laboratories that operate glow wire test equipment calibrated and validated in accordance with IEC 60695-2-10 to obtain internationally recognized test reports.
FAQ
What temperatures are used in glow wire testing of household appliances?
The standard temperature levels are 550°C, 650°C, 750°C, 850°C, and 960°C. The specific requirement depends on the part location, its function, the appliance power, and whether the appliance is normally operated unattended, as specified in clause 30.2 of IEC 60335-1 and GB 4706.1.
What is the difference between GWFI and GWIT?
GWFI is the glow-wire flammability index, which characterizes how a material burns and self-extinguishes after glow wire contact. GWIT is the glow-wire ignition temperature, which characterizes the lowest temperature at which the material ignites during the test. Both are material properties determined on flat test plates rather than finished parts.
What are the pass criteria for a finished part?
Generally, a finished part passes if it does not ignite, or if any flame or glowing combustion extinguishes within 30 seconds after removal of the glow wire, and if the tissue paper placed beneath the specimen does not ignite from burning drops. Specific clauses of the product standard may impose additional conditions.
How many samples are required for testing?
For end-product parts, typically three specimens of each part are tested at each temperature. For GWFI and GWIT determination on material plates, a minimum of three specimens is generally tested at each temperature level, and additional specimens may be needed to bracket the critical temperature.
Is glow wire testing mandatory for household appliances?
Yes. Fire hazard requirements, including glow wire testing, are mandatory under IEC 60335-1, EN 60335-1, and GB 4706.1, and they form part of the evidence required for certification schemes such as CCC. Compliance testing should be performed by laboratories with properly maintained apparatus and qualified personnel.