The plastic glow wire test is a fire-hazard screening method that evaluates how plastic materials and finished polymeric components behave when contacted by an electrically heated glowing wire, simulating the thermal stress of an overloaded connection or overheated electrical part. Performed in accordance with the IEC 60695-2 series and its EN and GB/T equivalents, the test generates flammability ratings such as GWT, GWFI, and GWIT that are mandated by product safety standards for appliances, luminaires, and electrical accessories worldwide. This article explains the test principle, sample requirements, test items, procedures, pass criteria, and typical applications of glow-wire testing for plastics.
Technical Overview
The glow wire test (also written as glow-wire test) is a standardized fire hazard test used to assess the flammability of non-metallic, primarily plastic, materials and finished parts. It simulates a realistic worst-case scenario in which an electrically heated element—such as an overheated resistor, a glowing conductor caused by an overloaded circuit, or a loose terminal connection—makes direct contact with a plastic surface for a defined period of time.
In the test, a nickel-chromium (80/20 Ni/Cr) resistance wire, 4 mm in diameter and bent into a specified shape, is electrically heated to a target temperature between 500 °C and 960 °C. The hot tip of the glow wire is then pressed against the specimen surface with a controlled force of 1.0 N ± 0.2 N for a contact duration of 30 s ± 1 s. A board of dry pine wood covered with a single layer of soft wrapping tissue is placed 200 mm ± 5 mm below the point of contact to determine whether flaming or glowing particles or drops falling from the specimen can ignite surrounding materials. The laboratory records whether ignition occurs, the ignition time (ti), the flame extinction time (te), whether the tissue paper ignites, and whether the specimen is completely consumed.
Glow wire testing is governed by a closely related family of standards:
- IEC 60695-2-10 / EN 60695-2-10 / GB/T 5169.10 — Glow-wire flammability test method: apparatus and common test procedure
- IEC 60695-2-11 / EN 60695-2-11 / GB/T 5169.11 — Glow-wire flammability test method for end products (GWEPT, commonly called GWT)
- IEC 60695-2-12 / EN 60695-2-12 / GB/T 5169.12 — Glow-wire flammability index (GWFI) test method for materials
- IEC 60695-2-13 / EN 60695-2-13 / GB/T 5169.13 — Glow-wire ignition temperature (GWIT) test method for materials
- ASTM D6194 — Standard test method for glow-wire ignition of materials (related method)
Testing Samples
Material Test Specimens (Plaques)
For material characterization under IEC 60695-2-12 and IEC 60695-2-13, test specimens are typically injection or compression molded plaques measuring 60 mm × 60 mm. The specimen thickness should correspond to the intended finished-part wall thickness, commonly between 0.75 mm and 3.0 mm, because glow wire results are thickness dependent. At least three specimens are required for each test temperature, and additional sets are needed when determining GWFI or GWIT across multiple temperature steps. Specimens should be free of flash, burrs, and surface contamination.
Finished Product and Component Samples
For the end-product test under IEC 60695-2-11, samples are complete finished products, sub-assemblies, or components tested in the condition in which they are supplied. The part is mounted in its normal use orientation, and the glow wire is applied to the most unfavorable accessible location—for example, the thinnest wall section or the area closest to current-carrying connections. A minimum of three identical samples or test locations is normally tested so that the most severe result governs the assessment.
Specimen Conditioning
Prior to testing, specimens are conditioned for at least 24 hours in standard laboratory conditions, typically 15 °C to 35 °C and 45 % to 75 % relative humidity. Testing is performed in a draft-free environment, since air movement can significantly influence ignition behavior and flame spread observations.
Testing Items
Accredited third-party laboratories typically offer the following glow wire test items for plastic materials and components:
- Glow-wire flammability test on end products (GWEPT/GWT) per IEC 60695-2-11, commonly at 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, or 960 °C
- Glow-wire flammability index (GWFI) of materials per IEC 60695-2-12, reported as the highest passing temperature (for example, GWFI 850 °C or GWFI 960 °C)
- Glow-wire ignition temperature (GWIT) of materials per IEC 60695-2-13, reported at a specified thickness (for example, GWIT 775 °C at 1.5 mm)
- Recorded test data: occurrence of ignition, ignition time (ti), flame extinction time (te), ignition of the wrapping tissue, production of flaming drops or particles, and whether the specimen is completely consumed
Testing Methods
Apparatus and Test Conditions
The test system comprises the glow-wire heating element, a temperature measurement and control unit, a specimen support carriage, and the tissue-covered pine board. The glow wire temperature is measured by a mineral-insulated, metal-sheathed, 1 mm diameter K-type (chromel-alumel) thermocouple welded to the top of the wire, and the system is periodically verified using silver foil, which melts at 960 °C. Key controlled parameters include the contact force of 1.0 N ± 0.2 N, the contact duration of 30 s ± 1 s, stable target temperature within the specified tolerance, and the 200 mm ± 5 mm distance between the contact point and the tissue layer.
Test Procedure
- Heat the glow wire to the specified target temperature and allow the system to stabilize, confirming the temperature reading with the calibrated thermocouple.
- Move the specimen toward the stationary glow wire (or vice versa) until the hot tip contacts the specimen surface, applying the specified force for 30 s ± 1 s.
- Observe and record whether the specimen ignites, the duration of flaming or glowing, the flame extinction time after removal of the glow wire, whether flaming drops fall, and whether the wrapping tissue is ignited.
- Repeat the test on at least three specimens at the same temperature; the most severe result determines the outcome at that temperature level.
- For GWFI and GWIT determinations, repeat the test sequence at successive temperature steps until the failure condition is identified, then assign the corresponding index or ignition temperature rating.
Pass Criteria and Ratings
- GWEPT (end products): The part is considered to pass at the selected temperature if it does not exhibit flaming or glowing that persists for more than 30 s after removal of the glow wire, and the wrapping tissue does not ignite.
- GWFI (materials): The highest temperature at which, in three consecutive tests, either no ignition occurs, or any flames or glowing extinguish within 30 s of glow wire removal, the specimen is not completely consumed, and the wrapping tissue does not ignite.
- GWIT (materials): Defined as the temperature 25 K higher than the highest temperature at which, in three consecutive tests, either no ignition of the specimen occurs, or flames and glowing extinguish within 30 s of removal of the glow wire and the wrapping tissue does not ignite.
Product safety standards commonly specify GWT requirements of 550 °C, 650 °C, 750 °C, or 850 °C depending on the function and proximity of the part to live connections, along with GWIT requirements such as 775 °C or 850 °C for parts supporting current-carrying connections in certain categories of appliances.
Applications
Glow wire testing is one of the most widely required fire hazard assessments for plastic materials and components in electrical and electronic products. Typical application areas include:
- Household and similar electrical appliances under IEC 60335-1: plastic enclosures, switches, internal supports, and insulating parts near electrical connections
- Luminaires under IEC 60598-1: lamp holders, diffusers, housings, and wiring compartment parts
- Audio/video, information, and communication technology equipment under IEC 62368-1: enclosures and components located near potential ignition sources
- Plugs, socket-outlets, and appliance couplers under IEC 60884-1 and IEC 60320: face plates, bodies, and terminal covers
- Low-voltage switchgear and controlgear under the IEC 60947 series: circuit breaker housings, contactor bodies, terminal blocks, and relay enclosures
- Medical electrical equipment under the IEC 60601-1 series: enclosures and insulating components
- Electric vehicle charging equipment and battery system components with elevated fire safety expectations
- Material development and quality control: generating GWFI and GWIT ratings for plastic datasheets, material certifications, and compliance dossiers prepared by accredited third-party laboratories
FAQ
What temperatures are used in the plastic glow wire test?
The glow wire can be set to standardized temperatures ranging from 500 °C to 960 °C, typically in steps of 50 K (500, 550, 600, 650, 700, 750, 800, 850, 900, and 960 °C). Product standards select the applicable severity level based on the part's location, function, and exposure to electrical connections.
What is the difference between GWT/GWEPT, GWFI, and GWIT?
GWT/GWEPT is a pass/fail assessment of a finished product or component at one specified temperature under IEC 60695-2-11. GWFI is a material flammability index under IEC 60695-2-12 expressed as the highest temperature at which the material passes the criteria. GWIT is a material ignition temperature under IEC 60695-2-13, defined as 25 K above the highest temperature at which the material does not ignite or self-extinguishes within 30 s in three consecutive tests.
How many samples are required?
For each test temperature, a minimum of three specimens is required. Determining a full GWFI or GWIT rating may require additional specimen sets because testing must be repeated at multiple temperature levels until the failure point is established.
Does the glow wire test replace other flammability tests such as UL 94?
No. The glow wire test simulates contact with a hot glowing element, while tests such as UL 94 assess ignition by a small flame. The two methods evaluate different fire hazard scenarios, and many product standards require both glow wire ratings and horizontal/vertical burning classifications for full compliance.
Can finished products be tested directly instead of material plaques?
Yes. IEC 60695-2-11 specifically covers end products and sub-assemblies, which are tested in their supplied condition in the normal use orientation. This is often the preferred route when material plaque data at the finished wall thickness is unavailable, although results apply only to the tested configuration.