Glow-wire test IEC 60695-2-11 — ignition risk of plastic enclosures

Almost every piece of electrical installation equipment — from a junction box to a distribution board — has a plastic enclosure. That enclosure must not only function mechanically and electrically, but also survive a realistic fault scenario: an internally glowing or overheated component (a loose terminal connection, an overloaded contact resistance) glowing locally against the inside of the enclosure. The glow-wire test per IEC 60695-2-11 simulates exactly that scenario.

What the test simulates

The glow-wire test mimics a glowing internal fault source — for example an overheated wire element or a glowing resistance from a poor connection — pressed against a plastic part of the enclosure. An electrically heated wire loop (the "glow wire") is brought to a standardised test temperature and pressed against the plastic surface under test for a fixed time (typically 30 seconds). It is then assessed whether the material:

ignites and self-extinguishes within a specified time after removal of the glow wire (without flaming droplets that could ignite underlying material), or
does not ignite at all.

The question is therefore not whether the material is non-combustible — almost no plastic is — but whether a localised, glowing fault source can cause a self-propagating fire that spreads beyond the point of direct contact.

GWFI versus GWIT: two different test results

GWFI (Glow-Wire Flammability Index): the highest test temperature at which the material may ignite, but self-extinguishes within the allowed time without flaming droplets that ignite underlying material. GWFI therefore describes flame self-extinguishing performance.
GWIT (Glow-Wire Ignition Temperature): the lowest test temperature at which the material actually ignites (with a flame burning for longer than a few seconds). GWIT is by definition at or above GWFI for the same material and therefore describes the ignition threshold itself.

Both values are expressed in degrees Celsius and correspond to specific test temperatures prescribed by the standard (among others 550, 650, 750, 850, and 960 C), not a freely chosen value. A manufacturer typically reports the test result at one of these standardised temperatures ("passed at 750 C GWFI"), not a continuous, arbitrary value.

Which test temperature for which application

The required test temperature depends on the risk level of the application and is typically differentiated in product standards (for example for switchgear and distribution assemblies, junction boxes, terminal blocks) according to the position of the part:

Parts that directly carry or enclose current-carrying connections (for example a terminal block, a contact carrier) are usually tested at the highest prescribed temperature, because a glowing fault scenario is most likely to occur directly here.
Parts that do not carry current-carrying components but are in their vicinity (for example an enclosure or cover) are often tested at a lower, but still relevant, temperature.

This explains why different plastic parts within one and the same device can be certified against different glow-wire temperatures, depending on their function and position.

Practical significance for material selection and assessment

When assessing installation equipment — particularly non-CE-marked or questionable equipment, or when replacing a part with a non-original alternative — it is relevant to verify that the plastic used actually has a glow-wire certification appropriate to its position within the device. A plastic part without (or with too low) a glow-wire classification at a position where it can come into direct contact with a glowing fault source increases the risk that a locally limited connection fault escalates into a self-propagating fire within the enclosure — one of the recognised causes of electrical fires, which is also relevant as background in the overview of fire-extinguishing media for electrical installations.

Typical mistakes

Assuming CE marking automatically guarantees an adequate glow-wire classification — CE marking confirms conformity with the applicable directives, but the specific glow-wire test temperature and whether it is appropriate for the application must be separately verified from the product documentation or test certificate.
Confusing GWFI and GWIT — a material that "passes" at a given temperature under GWFI may still ignite at that same temperature; it is the self-extinguishing performance that has been approved, not the absence of ignition.
Replacing a part with a visually similar plastic alternative without checking whether that material has the same glow-wire classification as the original, particularly for parts that carry current-carrying connections.
Assessing the test temperature of the enclosure as a whole instead of per part — different plastic components within the same device can, depending on their function, be certified against different temperatures.