Glow Wire Testing of Plastics: Standards, Methods, GWFI, GWIT and GWEPT Explained

Glow wire testing is a fire-hazard evaluation method that determines how plastic materials and finished polymer components behave when they come into contact with an electrically heated, glowing metal element. Based on the IEC 60695-2 series of standards and their EN and GB/T equivalents, the method yields key safety indicators such as the glow-wire flammability index (GWFI), the glow-wire ignition temperature (GWIT), and end-product glow-wire flammability (GWEPT). This article explains the testing principles, sample requirements, procedures, acceptance criteria, and typical applications of glow wire testing for plastics.

Technical Overview

Glow wire testing (GWT) simulates the thermal stress that polymeric materials may experience when exposed to a glowing or red-hot metal part, for example an overloaded resistor, a degraded electrical connection, or a conductor carrying fault current. During the test, a standardized loop of nickel-chromium wire is heated electrically to a defined temperature and pressed against the surface of a specimen under controlled force and duration. The behavior of the specimen, including whether it ignites, how long it burns, and whether burning drops fall away, is used to assess its contribution to fire hazard.

The method family is standardized in IEC 60695-2-10 through IEC 60695-2-13, adopted in Europe as the EN 60695-2 series and in China as GB/T 5169.10 through GB/T 5169.13. Numerous product safety standards, such as IEC 60335-1 for household appliances, IEC 60598-1 for luminaires, IEC 62368-1 for audio/video and IT equipment, IEC 60884-1 for plugs and socket-outlets, and IEC 61058-1 for switches, assign glow-wire temperature requirements to components according to their function and proximity to live connections.

• IEC 60695-2-10 / GB/T 5169.10 – Glow-wire apparatus and common test procedure
• IEC 60695-2-11 / GB/T 5169.11 – Glow-wire flammability test for end-products (GWEPT)
• IEC 60695-2-12 / GB/T 5169.12 – Glow-wire flammability index for materials (GWFI)
• IEC 60695-2-13 / GB/T 5169.13 – Glow-wire ignition temperature for materials (GWIT)

Accredited third-party laboratories routinely perform these tests to support product certification, material preselection, quality control, and regulatory compliance for electrical and electronic products worldwide.

Testing Samples

Flat Material Specimens

Material characterization tests (GWFI and GWIT) use flat plaques measuring 60 mm × 60 mm. Preferred thicknesses are 0.75 mm ± 0.1 mm, 1.5 mm ± 0.1 mm, and 3.0 mm ± 0.2 mm, and the thicknesses tested should match the minimum and maximum wall thicknesses used in the end product. A minimum of three specimens is tested at each temperature, and specimens are conditioned for at least 24 hours at 23 °C ± 2 °C and 50 % ± 5 % relative humidity before testing.

Finished Components and End Products

The end-product test (GWEPT) is performed on complete parts or on sections cut from finished goods, mounted in the attitude of normal use. Typical tested items include terminal blocks, switches, socket outlets, connectors, relay housings, coil formers, fan blades, insulating barriers, and enclosure sections located close to current-carrying connections. A layer of tissue paper placed on a pine board approximately 200 mm below the contact point is used to detect ignitable burning drops.

Common Polymer Families

• Engineering thermoplastics: PA6, PA66, PBT, PET, PC, PC/ABS blends, PPS, PPO/PPE
• General-purpose thermoplastics: ABS, PS, HIPS, PP, PE, PVC, PMMA, POM
• Soft and elastic materials: TPE, TPU and silicone-based parts in applicable forms
• Thermosetting materials: phenolic moulding compounds, epoxy, unsaturated polyester, melamine

Both flame-retarded (halogenated and halogen-free) and unfilled or reinforced grades can be evaluated. Test results are specific to the material formulation, thickness, and colour as submitted.

Testing Items

• Glow-Wire Flammability Index (GWFI) per IEC 60695-2-12 / GB/T 5169.12, expressed as the highest temperature, for example 550, 600, 650, 700, 750, 800, 850, 900 or 960 °C, at which the pass criteria are met
• Glow-Wire Ignition Temperature (GWIT) per IEC 60695-2-13 / GB/T 5169.13, reported in °C as the temperature 25 K above the highest temperature at which no sustained ignition occurs
• Glow-Wire Flammability of End Products (GWEPT) per IEC 60695-2-11 / GB/T 5169.11 at the temperature mandated by the applicable product standard, commonly 550, 650, 750, 850 or 960 °C
• Recorded observations: ignition of the specimen, afterflame and afterglow duration, flaming or glowing drops, and ignition of the tissue paper indicator

Testing Methods

Apparatus and Calibration

• Glow wire made of nickel-chromium (NiCr 80/20) alloy, bent into a loop with a 4 mm tip diameter
• Fine-wire thermocouple (0.5 mm diameter) welded to the tip to measure the contact temperature
• Tip temperature verified with pure silver foil, which melts at 960 °C, confirming calibration accuracy
• Contact force of 1.0 N ± 0.2 N applied for 30 s ± 1 s, with penetration depth mechanically limited to 7 mm
• Glow-wire temperature stabilized within ±10 K for at least 60 s before each application

Glow-Wire Flammability Index (GWFI)

The specimen is clamped with its surface vertical, and the heated glow-wire tip is pressed horizontally against it. At a given temperature, the test is passed if, for three consecutive specimens, the material does not ignite, or any flames extinguish within 30 s after removal of the glow wire, and no flaming drops ignite the tissue paper placed below. Testing proceeds through the standard temperature steps, and the GWFI is the highest temperature at which the criteria are satisfied. The result is reported, for example, as GWFI 850 °C (IEC 60695-2-12).

Glow-Wire Ignition Temperature (GWIT)

For GWIT, specimens are exposed to a series of increasing temperatures. At each temperature, three specimens are evaluated, and the observation of interest is whether ignition occurs, defined as flaming or glowing that persists for longer than 5 s after removal of the glow wire, or any ignition of the tissue paper. The GWIT is the temperature 25 K above the highest tip temperature at which three consecutive specimens show no ignition. Product standards frequently set GWIT limits 25 K above the applicable glow-wire temperature, for instance 775 °C where a 750 °C glow-wire requirement applies.

End-Product Glow-Wire Flammability Test (GWEPT)

The finished part is mounted as in normal service, and the glow wire is applied to the most onerous positions, typically adjacent to current-carrying connections, at the thinnest sections, or on surfaces where ignition is most likely. The usual acceptance criteria require that no flame or glowing persist for more than 30 s after removal of the glow wire and that the tissue paper and adjacent parts not be ignited; individual product standards may define additional or alternative criteria.

Applications

• Household and similar electrical appliances (IEC 60335-1): enclosures and decorative parts at 550 °C; parts supporting or in contact with current-carrying connections at 750 °C, raised to 850 °C for unattended appliances
• Luminaires and lighting components (IEC 60598-1): insulating parts retaining live parts and parts near ignitable components tested at temperatures between 650 °C and 960 °C depending on location and luminaire type
• Audio/video, information and communication equipment (IEC 62368-1 and its predecessor IEC 60950-1): material preselection and component evaluation at 550 °C, 650 °C or 750 °C
• Plugs, socket-outlets and couplers (IEC 60884-1), switches (IEC 61058-1), and automatic electrical controls (IEC 60730-1): glow-wire requirements for parts that retain or are in contact with live parts
• Low-voltage switchgear and controlgear assemblies: verification of polymeric parts in accordance with the IEC 60947 series
• Material development, incoming inspection, supplier qualification, and certification support by manufacturers and accredited third-party laboratories

FAQ

What is the difference between GWFI and GWIT?

GWFI describes how well a material resists sustained burning after contact with a hot element, meaning the highest temperature at which flames self-extinguish within 30 s and no drips ignite the tissue paper. GWIT identifies the threshold temperature at which the material first sustains ignition, reported as 25 K above the highest temperature at which no ignition occurs. The two values are complementary and are often quoted together, for example GWFI 960 °C and GWIT 775 °C.

Which glow-wire temperatures are most commonly required?

The most frequently specified temperatures are 550 °C, 650 °C, 750 °C, 850 °C and 960 °C. The exact requirement depends on the product standard, the function of the part, whether it supports a current-carrying connection, and whether the appliance operates while attended or unattended.

How does glow-wire testing differ from needle-flame and UL 94 burning tests?

Glow-wire tests apply a hot solid element and evaluate ignition caused by thermal contact, whereas the needle-flame test (IEC 60695-2-2) applies a small gas flame and UL 94 or IEC 60695-11-10 tests apply a burner flame to assess flame propagation. The methods are complementary: glow-wire data address faults involving overheated components, while flame tests address exposure to small open flames.

Can material test results replace testing the finished product?

No. GWFI and GWIT values characterize a material at a defined thickness and provide a basis for preselection, but the geometry, wall thickness, proximity to other parts, and heat dissipation of the final component can change its fire behavior. Product standards therefore require the end-product glow-wire test on the actual part unless a specific material-route clause applies.

How many specimens are required, and how is testing organized?

At least three consecutive specimens must meet the criteria at each temperature. For GWFI and GWIT, laboratories typically test a temperature ladder, so a full characterization may require ten or more specimens. Each exposure lasts 30 s, but the complete sequence, including conditioning, calibration checks, and multiple temperature steps, usually takes several working days.

Are GB/T and EN versions of the standard equivalent to IEC 60695-2?

Yes. GB/T 5169.10 through GB/T 5169.13 and the EN 60695-2 series are national and regional adoptions of the corresponding IEC standards, with substantially identical apparatus, procedures, and criteria. Results from accredited third-party laboratories aligned with IEC 60695-2 are therefore widely accepted across markets.

What are the most common failure modes?

Failures typically involve afterflame longer than the permitted time, flaming drips that ignite the tissue paper, or ignition at a temperature below the level required by the product standard. Corrective actions usually include selecting a higher flame-retardant grade, increasing wall thickness, or redesigning the part so that the material is farther from potential heat sources.