what is glow wire test？

I. Overview

The glow wire test is a standardized test method used to evaluate the flame resistance of electrical and electronic products and their materials under simulated overheating or fault conditions. This test simulates high-temperature heat sources generated by electrical components due to overload, short circuit, or poor contact, examining the ignition characteristics, burning duration, and ignition of surrounding materials when in contact with a high-temperature metal wire, thereby assessing their fire risk in actual use.

As an important component of a series of fire hazard testing standards developed by the International Electrotechnical Commission (IEC), the glow wire test has been adopted as a mandatory safety test item by major global certification systems (such as CE, CCC, UL, etc.) and is widely used in household appliances, information technology equipment, automotive electronics, and rail transportation.

II. Test Principle

The core of the glow wire test lies in simulating flameless heat sources that may occur under real-world operating conditions. The test apparatus mainly consists of the following parts:

● Glow Wire Assembly: Typically made of a U-shaped ring using a 4 mm diameter nickel-chromium (Ni/Cr) alloy wire, possessing good high-temperature resistance and electrical stability.

● Heating System: Heats the glow wire using a low voltage and high current to reach a preset temperature (typically between 550℃ and 960℃).

● Temperature Control System: Utilizes thermocouples to monitor the temperature at the tip of the glow wire in real time, ensuring temperature deviation is controlled within ±10℃ during the test.

● Mechanical Transmission Mechanism: Controls the glow wire to approach the sample at a specified speed (10–25 mm/s), maintain contact for a specified time (usually 30 s), and then automatically withdraw.

● Observation and Recording System: Includes a flame detection sensor, a timer, and a standard silk paper laid underneath to determine whether ignition occurs and whether the molten droplets initiate secondary combustion.

During the test, the tip of the glow wire is vertically pressed into the sample surface with a pressure not exceeding 1.05 N, with a penetration depth limited to 7 mm ± 0.5 mm. During this period, the operator or automated system must record the following key parameters:

● Whether a visible flame occurs;

● Flame duration (Te);

● Whether the molten droplets ignite the silk paper below;

● Sample self-extinguishing time.

III. Relevant Terminology and Evaluation Indicators

According to the IEC 60695 series of standards, the glow wire test involves three core concepts, each corresponding to different testing purposes and evaluation methods:

1. Glow Wire Flammability Index (GWFI)

As defined in IEC 60695-2-10 / GB/T 5169.10, GWFI refers to the highest glow wire temperature at which a standard-sized specimen (typically 30 mm × 6 mm × thickness) does not produce sustained combustion (i.e., the flame extinguishes within 30 seconds after the glow wire is removed and does not ignite the paper) in three consecutive tests under specified conditions. This index is used for grading the flame retardant properties of materials and is commonly used for raw material screening and quality control.

For example: A GWFI of 850℃ for a certain plastic material indicates that it passes the test at 850℃ but fails at 900℃.

2. Glow Wire Ignition Temperature (GWIT)

As defined in IEC 60695-2-12 / GB/T 5169.12, GWIT refers to the lowest glow wire temperature at which a sample can ignite at a specific heating rate. Unlike GWFI, GWIT focuses on the critical point of "initial ignition" rather than overall flammability. Its testing process is more refined, typically starting at a lower temperature and gradually increasing until the first stable flame is observed.

GWIT values are generally higher than GWFI because even if the material is ignited, it may possess rapid self-extinguishing capabilities.

3. Finished Product Glow Wire Test (GWT or GWEPT)

Performed according to IEC 60695-2-11 / GB/T 5169.11, this is a practical application-level test for the final product or its components (non-standard specimens). The test temperature is clearly specified by the product safety standard (e.g., 750°C or 850°C is commonly used for household switches). The judgment criteria are:

● The sample does not ignite; or

● Although it ignites, the flame extinguishes within 30 seconds after the hot wire is removed, and the molten droplets do not ignite the underlying silk paper.

This method is closer to actual use scenarios and is the main basis for type testing and certification testing.

IV. Applicable Standards System

The glow wire test follows a complete international standards framework, mainly including:

The above standards have been converted into Chinese national standards GB/T 5169.10~13 series and incorporated into several industry mandatory specifications, such as:

● GB 4706.1 "Safety of household and similar electrical appliances - Part 1: General requirements"

● GB 4943.1 "Information technology equipment - Safety - Part 1: General requirements"

● UL 746A (USA) on short-term performance evaluation of polymer materials

V. Application Scenarios and Significance

The glow wire test is particularly suitable for evaluating non-metallic materials that may come into contact with high-temperature components during normal operation, including but not limited to:

● Housings of switches, sockets, and terminals;

● Relay and transformer frames;

● Circuit board supports;

● Internal insulation partitions of household appliances;

● Connector sheaths for automotive wiring harnesses.

Compared to open flame tests (such as UL94 horizontal/vertical burning tests), the glow wire test better reflects the slow heat accumulation effect caused by resistance heating, and is particularly suitable for evaluating material behavior in the absence of an external flame source. Therefore, it plays an irreplaceable role in preventing electrical fires.

Furthermore, with the development of new energy vehicles, energy storage systems, and smart grids, the requirements for the heat resistance of materials in high-power-density devices are increasing, further highlighting the importance of the glow wire test.

VI. Recommended Products:Glow-wire tester

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Glow-wire testerwill stipulate the material (diameter 4mm, Ni77/Cr20±1) and the shape of U-shaped heating wire with a high current heating to the test temperature (200 ℃ ~ 1250 ℃) 1min, after the prescribed pressure (1.0N) vertical scalding test specimens for 30s, depending on whether the test specimens and bedding ignition or holding time to determine the electrical and electronic equipment products.

The flammability, glow-wire ignition temperature (GWIT), flammability and glow-wire flammability index (GWFI) of solid insulating materials and other solid combustible materials are determined.

VII. Conclusion

The glow wire test is a rigorous and widely used scientific method for fire safety assessment. By accurately simulating thermal stress conditions in electrical faults, it effectively identifies the potential fire risks of materials under extreme conditions. Through the proper application of the three indicators—GWFI, GWIT, and GWT—manufacturers can optimize material selection during the product design phase, improving overall safety while meeting global market compliance requirements.

In the future, with advancements in testing technology and the widespread adoption of intelligent equipment, the glow wire test will continue to improve in terms of data acquisition accuracy, result repeatability, and automation, providing stronger technical support for the inherent safety of electrical products.