Glow-Wire Combustion Testing of Plastic Materials: Principles, Standards, and Applications

Glow-wire combustion testing is an internationally recognized fire-hazard assessment method that evaluates how plastic materials and finished components respond to contact with an electrically heated glowing element, as specified in the IEC 60695-2 series and its GB/T 5169 equivalents. This article explains the test principle, specimen requirements, key indices such as GWFI and GWIT, pass criteria, and typical application scenarios, helping manufacturers select compliant materials and prepare specimens for evaluation at accredited third-party laboratories.

Technical Overview

The glow-wire combustion test is a fire-hazard simulation method used to assess the ignitability and flame-propagation behavior of polymeric materials and components used in electrical and electronic products. It reproduces, in a reproducible laboratory manner, the thermal stress that a component may impose on its surroundings under fault conditions, such as an overloaded or glowing resistor, a loose terminal connection, or contact with a heated metallic element. During the test, the tip of an electrically heated nickel-chromium (NiCr 80/20) wire, typically 4 mm in diameter, is pressed against the surface of a test specimen at a defined temperature and force, and the ignition behavior, flame duration, and production of flaming droplets are evaluated.

The core methodology is defined by the IEC 60695-2 series: IEC 60695-2-10 covers the glow-wire apparatus and the common test procedure, IEC 60695-2-11 specifies the glow-wire flammability test (GWT) for end products, IEC 60695-2-12 defines the glow-wire flammability index (GWFI) for materials, and IEC 60695-2-13 defines the glow-wire ignition temperature (GWIT) for materials. These documents are adopted in Europe as the EN 60695-2 series and in China as the GB/T 5169.10 through GB/T 5169.13 series, and they are widely referenced by product safety standards including IEC 60335-1, IEC 60598-1, IEC 60950-1, IEC 62368-1, IEC 60601-1, and various UL end-product standards.

Testing Samples

Material Test Specimens for GWFI and GWIT

Material characterization tests use flat plates, normally 60 mm × 60 mm in size. The preferred thicknesses are 0.75 mm ± 0.1 mm, 1.5 mm ± 0.1 mm, and 3.0 mm ± 0.2 mm; other thicknesses representative of the end application may be evaluated, but the thickness must always be reported because ignition behavior is strongly thickness-dependent. Specimens are typically injection-molded or cut from compression-molded or extruded sheet. A minimum of three fresh specimens is required for each temperature level tested.

Finished-Product Components for GWT

End products and components, such as enclosures, covers, switch actuators, terminal blocks, connectors, coil formers, and insulating barriers, are tested in the condition in which they are delivered. The component is mounted in its normal operating position, with the surface to be contacted oriented vertically, and the glow-wire tip is applied to the most unfavorable location that could realistically come into contact with a glowing element in service. Supporting fixtures must not distort heat transfer to the specimen.

Conditioning and Quantity

Unless otherwise specified, specimens are conditioned for at least 24 hours at 15 °C to 35 °C and 45 % to 75 % relative humidity immediately before testing. Because a full GWFI or GWIT determination may involve several temperature levels, clients submitting samples to accredited third-party laboratories are generally advised to provide at least 10 to 20 specimens plus spares.

Testing Items

• Glow-Wire Flammability Test (GWT) of end products per IEC 60695-2-11 / GB/T 5169.11, evaluating whether a finished part ignites and whether burning drops or particles ignite surrounding materials.
• Glow-Wire Flammability Index (GWFI) of materials per IEC 60695-2-12 / GB/T 5169.12, the highest temperature from the standard severity list at which the material either does not ignite or self-extinguishes within 30 seconds after removal of the glow-wire without igniting the tissue paper and board placed beneath it.
• Glow-Wire Ignition Temperature (GWIT) of materials per IEC 60695-2-13 / GB/T 5169.13, expressed as 25 K (or 30 K where the relevant specification requires) above the highest temperature at which none of three consecutive specimens ignites.

Test temperatures are selected from the standard severity levels of 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, and 960 °C, depending on the requirements of the applicable product standard.

Testing Methods

Apparatus and Calibration

The test system comprises a temperature-controlled glow-wire made of 4 mm diameter nickel-chromium wire formed into a defined tip geometry, a 1.0 mm diameter sheathed fine-wire thermocouple fitted at the tip to measure its temperature, a force-application mechanism that maintains a contact force of 1.0 N ± 0.2 N, and a specimen carriage that limits the penetration of the glow-wire into the specimen to a maximum of 7 mm. The heating and control system is verified using pure silver foil, which melts at approximately 960 °C, together with thermocouple calibration, to confirm the accuracy of the applied temperature. A pine board approximately 10 mm thick, covered with a single layer of soft tissue paper, is positioned 200 mm ± 5 mm below the point of contact to catch and register any flaming drops or particles.

Test Procedure

• Heat the glow-wire tip to the selected temperature and allow it to stabilize within a tolerance of ±10 K in a substantially draught-free enclosure.
• Bring the specimen into contact with the tip at a controlled, slow approach speed, maintaining a force of 1.0 N ± 0.2 N with penetration not exceeding 7 mm, for a contact duration of 30 seconds.
• Observe and record the time to ignition (Ti), the moment of withdrawal, and the time at which flames or glowing extinguish after withdrawal (Te).
• Record whether any burning drops or particles fall and whether they ignite the tissue paper or char the pine board.
• Classify the result against the pass criteria of the relevant part of IEC 60695-2, using fresh specimens for each repeat test.

Pass Criteria and Evaluation

For the glow-wire flammability test on end products, the specimen is deemed to have passed if it does not ignite, or if any flames extinguish within 30 seconds after removal of the glow-wire and the underlying tissue paper does not ignite. For GWFI, the index is the highest severity temperature at which this condition is satisfied in three consecutive tests. For GWIT, testing proceeds at successive severity temperatures until the highest level at which no ignition occurs in three consecutive tests is established, and the reported GWIT is 25 K (or 30 K where specified) above that temperature.

Applications

Glow-wire testing is one of the most widely mandated fire-safety evaluations for plastics in electrical and electronic products, and its results directly support material selection, design qualification, and regulatory compliance.

• Household and similar electrical appliances under IEC 60335-1, where enclosures and parts located near current-carrying connections commonly require 750 °C or 850 °C performance, and other non-metallic parts 550 °C or 650 °C depending on their function.
• Information technology, communication, and audio/video equipment under IEC 62368-1 and the former IEC 60950-1 and IEC 60065, where fire-enclosure materials are frequently qualified by GWFI of 850 °C or a comparable GWIT level.
• Luminaires and lighting components under IEC 60598-1, including lamp holders, terminal compartments, and insulating parts, with typical severities of 650 °C and 850 °C.
• Low-voltage switchgear and controlgear, wiring accessories, plugs and socket-outlets, and terminal blocks under the IEC 60947, IEC 60884, and IEC 60998 families, which frequently specify severities up to 850 °C or 960 °C.
• Medical electrical equipment under IEC 60601-1, where non-metallic parts are evaluated according to their proximity to potential ignition sources.
• Material research and development, incoming quality control, and supplier qualification for engineering plastics such as PC, ABS, PA, PBT, PP, POM, and PVC compounds.

FAQ

The following questions address the most common technical and commercial concerns raised by manufacturers preparing plastic materials and components for glow-wire evaluation at accredited third-party laboratories.

What is the difference between GWFI and GWIT?

GWFI characterizes the ability of a material either to resist ignition altogether or to self-extinguish within 30 seconds after the glow-wire is removed without igniting the tissue paper below, while GWIT characterizes ignition tendency and is reported as 25 K or 30 K above the highest temperature at which no ignition occurs in three consecutive tests. Product safety standards specify one index or the other depending on the function and location of the part.

Which temperature level applies to my product?

The required severity is dictated by the applicable product standard and by the function of the part, for example whether it retains live parts in position, is located near an uninsulated connection carrying significant current, or serves merely as a decorative element. Common requirements range from 550 °C for minor parts to 850 °C or 960 °C for parts in contact with current-carrying connections.

How many specimens should I prepare?

A minimum of three fresh specimens is needed per temperature point, and a complete GWFI or GWIT determination across multiple severity levels typically consumes 10 to 20 specimens. Laboratories generally recommend submitting surplus specimens because re-testing at additional temperatures is frequently required.

Does passing the glow-wire test replace other fire-hazard tests?

No. Glow-wire testing addresses thermal stress caused by electrically heated or glowing elements. It complements other evaluations such as needle-flame testing under IEC 60695-2-2 and horizontal or vertical burning tests under UL 94 and IEC 60695-11-10, and certification schemes often require a combination of these tests.

Can a finished product be tested instead of the raw material?

Yes. IEC 60695-2-11 is designed for end products and components tested in their as-delivered state, whereas GWFI and GWIT are material indices determined on standardized plates. The appropriate route depends on the clauses of the governing product standard.

What are the most common failure modes and remedies?

Typical failures include sustained flaming for more than 30 seconds after withdrawal, flaming droplets that ignite the tissue paper, and burn-through of the specimen. Effective remedies include selecting more thermally stable or flame-retardant grades, increasing wall thickness, adding insulating barriers, and redesigning the part to distance polymeric material from potential ignition sources.