Last updated: 2026-09-05 · 5 min read

Glow Wire Test (IEC 60695) — What Is the Difference Between GWFI and GWIT, and Which Resins Pass at 960°C?

The glow wire test (IEC 60695-2-10/11/12) simulates a heated component pressing against a plastic surface. Two metrics: GWFI (Glow Wire Flammability Index) is the highest temperature at which the material self-extinguishes within 30s; GWIT (Ignition Temperature) is where sustained flaming exceeds 2s. For EU electrical equipment, GWFI 960°C is the minimum — only PPS, PEI, PEEK and mineral-filled nylon pass without additives.

Key Facts

  • The test presses a Nichrome wire (4mm diameter) heated to a set temperature (550–960°C) against the specimen for 30 seconds. GWFI is the highest temperature where no flaming lasts more than 30s after wire removal and the tissue paper beneath does not ignite. GWIT is the temperature where sustained flaming (>2s) occurs — typically 50–100°C higher than GWFI for the same material.
  • GWFI differs from the vertical burn test (UL94 V-0). UL94 uses an open flame — it tests ignitability from a flame source. The glow wire test uses a heated metal surface — it tests ignitability from thermal contact. A resin can pass V-0 but fail the glow wire test at 750°C. Halogenated FR additives that work for UL94 do not necessarily improve GWFI — mineral fillers are more effective for glow wire resistance. See the UL94 flame rating guide for how the two tests differ in mechanism and resin response.
  • The glow wire test is mandatory for electrical equipment sold in the EU (IEC 60335-1, IEC 60950-1, IEC 61439). Required GWFI depends on application: 650°C for non-load-bearing parts, 750°C for load-bearing parts, 850–960°C for parts near live conductors. If your part fails the required GWFI, it cannot be sold in the EU regardless of its UL94 rating.

How Do Common Engineering Resins Compare on GWFI and GWIT?

Resin GWFI (3mm) GWIT (3mm) Additive Required?
PPS GF40 960°C 960°C No (inherent)
PEI (ULTEM) 960°C 960°C No (inherent)
PEEK 960°C 960°C No (inherent)
PA66 GF30 + mineral FR 960°C 850°C Mineral FR
PBT GF30 + mineral FR 960°C 800°C Mineral FR
PC FR grade 850°C 750°C Phosphorus FR
ABS FR grade 750°C 650°C Brominated FR
PA66 GF30 (unfilled) 650°C 550°C No additive

GWFI vs GWIT — GWFI (Glow Wire Flammability Index) is a pass/fail test at a set temperature: the highest temp where the specimen self-extinguishes within 30s. GWIT (Glow Wire Ignition Temperature) is the actual ignition threshold: the temp where sustained flaming exceeds 2s. GWIT is typically 50–100°C higher than GWFI for the same material. Product standards specify GWFI; GWIT is for material comparison only.

PPS, PEI and PEEK achieve GWFI 960°C inherently — the same three resins that achieve inherent V-0 in the vertical burn test. For nylon and PBT, mineral-filled FR grades are needed to reach 960°C. Standard glass-filled grades without FR only reach 650°C GWFI — insufficient for most electrical applications.

What Three Design Rules Govern Glow Wire Compliance for Electrical Parts?

  1. Test at the actual part wall thickness — GWFI drops 100–200°C when wall decreases from 3mm to 1.5mm. The test uses 3mm bars. At 1.5mm wall, GWFI may drop from 960°C to 750–850°C because thinner sections have less thermal mass. Request GWFI data at your actual wall thickness from the resin supplier. If unavailable, mold test bars at your part thickness and test.
  2. Color affects GWFI — carbon black reduces it by 50–100°C; titanium dioxide has minimal effect. Carbon black absorbs heat and promotes pyrolysis. A PPS GF40 that passes 960°C in natural color may only pass 850°C in black. For GWFI 960°C in black, switch from PPS to PEI or PEEK — their inherent flame resistance overcomes the carbon black effect. See the PEI processing guide for PEI parameters at GWFI 960°C in black.
  3. Creepage distance determines required GWFI — proximity to live conductors sets the bar. IEC 60335-1 specifies: parts >3mm from live conductors need GWFI 650°C; parts within 3mm need 750°C; parts in contact need 850–960°C. Design to maximize the distance between plastic and live conductors — even 1–2mm of air gap can reduce the required GWFI from 960°C to 750°C.

Creepage distance — the shortest path along the surface of an insulating material between two live conductors. IEC 60335-1 uses creepage distance to determine the required GWFI: >3mm = 650°C, within 3mm = 750°C, in contact = 850–960°C. Increasing creepage by even 1–2mm can drop the required GWFI by 200°C, opening up more resin options.

Glow wire test (IEC 60695-2-10/11/12): Nichrome wire at 550–960°C pressed on plastic for 30s. GWFI: highest temp self-extinguishes in 30s. GWIT: temp where sustained flaming >2s. Mandatory for EU electrical equipment. PPS/PEI/PEEK pass 960°C inherently. Wall thickness and color affect results.

  • Required GWFI confirmed by creepage distance — >3mm from live parts: 650°C; within 3mm: 750°C; in contact: 850–960°C.
  • Tested at actual part wall thickness — GWFI drops 100–200°C when wall decreases from 3mm to 1.5mm.
  • Color package verified — carbon black reduces GWFI by 50–100°C; natural or white grades have higher margin.
  • Inherent GWFI 960°C resins evaluated — PPS, PEI, PEEK without additives; mineral FR for nylon/PBT.
  • Both GWFI and UL94 V-0 required — design to the stricter test; PPS/PEI/PEEK pass both without FR additives.

Frequently Asked Questions

What is the difference between GWFI and GWIT, and which one do I need to specify?

GWFI measures the highest temperature at which the material self-extinguishes within 30s — it is a pass/fail test at a set temperature. GWIT measures the temperature at which the material sustains flaming for more than 2s — it is the actual ignition threshold. Product standards (IEC 60335, IEC 60950) specify the required GWFI (typically 850°C or 960°C). GWIT is used for material comparison — a higher GWIT means more margin against ignition.

For part approval, GWFI is the relevant metric. If your product standard requires GWFI 850°C at 3mm, the part is tested at 850°C and must self-extinguish within 30s with no tissue paper ignition.

Can a resin pass the vertical burn test (V-0) but fail the glow wire test?

Yes — the two tests use different ignition mechanisms. The vertical burn test uses an open flame; the glow wire test uses a heated metal surface. A halogenated FR PC that passes V-0 at 1.5mm may only pass GWFI 750°C because brominated FR works against flame chemistry but not against hot-surface ignition.

Conversely, a mineral-filled PPS that passes GWFI 960°C needs no FR additive for V-0 because its aromatic backbone resists both flame and hot-surface ignition. For equipment that must meet both V-0 and GWFI 960°C, PPS, PEI and PEEK are the only options without additives.

Does the glow wire test apply to products sold in North America?

Not directly — North American standards (CSA C22.2 No. 60335-1) reference the glow wire test but with lower requirements: 650°C for non-load-bearing parts, 750°C for load-bearing parts. For IT equipment, the North American standard does not require the glow wire test — it uses the vertical burn test (UL94 V-0) instead.

If your product is sold globally (both EU and North America), design to the stricter requirement — GWFI 960°C covers both markets and simplifies the approval process by using a single resin grade for all regions.

Key Takeaways

  • Glow wire test (IEC 60695): hot wire at 550–960°C for 30s.
  • GWFI: highest temp self-extinguishes in 30s. GWIT: ignition threshold.
  • Mandatory for EU electrical: 650–960°C depending on proximity to live parts.
  • PPS/PEI/PEEK pass 960°C inherently. Mineral FR needed for nylon/PBT.

Send the part drawing with the required GWFI, the wall thickness and the color — the quotation specifies whether the resin achieves the GWFI inherently (PPS, PEI, PEEK) or requires a mineral-filled FR grade, and whether the color package affects the rating.

Sources: IEC — IEC 60695-2-10/11/12 Glow Wire Test Methods and IEC 60335-1 Appliance Safety Standard · BASF — Ultramid GWFI Data Sheets and Electrical Application Guidelines · Plastics Technology — Glow Wire Flammability Testing and Resin Comparison Data · Society of Plastics Engineers (SPE) — Electrical Flammability Technical Papers · MatWeb — Material Property Database with GWFI and GWIT Values

— Arthur, Tooling Engineer at aCatMould