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Principle of the Glow Wire Test Instrument

The glow wire test instrument simulates the situation where insulating materials or other solid combustible materials within equipment that are prone to flame spread may ignite due to a hot wire or hot component.

Under certain conditions, such as fault current flowing through a conductor, component overload, and poor contact, some components may reach a certain temperature and cause the nearby parts to ignite. This test is conducted under such circumstances.

The working principle of the glow wire test instrument:

A nickel-chromium wire (U-shaped hot wire head) of specified material and Φ4mm is heated to the test temperature (300℃ to 1000℃) by a large current, and then the test sample is horizontally scalded for 30 seconds at a specified pressure (1.0N).

The fire hazard of finished electrical and electronic equipment is determined by whether the test specimen and the bedding material ignite or sustain combustion. After the test, the scorching time, ignition time (Ti), flame extinction time (Te), and flammability index (GWFI) are recorded.

Glow wire tip:

The temperature of the glow wire is measured by a fine thermocouple with a nominal diameter of 0.5mm, made of nickel-chromium and nickel-aluminum (Type K) wires, suitable for continuous operation at temperatures up to 960°C. The welding point of the thermocouple is located inside the armored sheath, and the metal of the armored sheath should be able to withstand a temperature of at least 1050°C for the thermocouple used to measure the temperature of the glow wire.

Calibration of glow wire temperature:

1. Place the silver foil (purity 99.8%, thickness 0.06mm, 2mm square) required by the standard at the center of the top of the hot wire tip.

2. Heat the glow wire tip to an appropriate value until the silver foil melts. At this point, the value indicated by the thermometer should be 960±15°C as required by the relevant standard.

Note: The metal of the armored sheath of the thermocouple used to test the temperature of the glow wire should be able to withstand a temperature of at least 1050°C. It is recommended to use imported thermocouples.