The test procedure is used to examine the fire resisting properties of products if, during the application or in the case of a fault, heated or glowing parts could be considered as a short-time ignition source. Loose connections or bad contacts cause punctually high temperatures on electrical articles, their components and their parts. Attention should also be paid to the fire risk in connection with textile seat coverings, tablecloths,or curtains, e.g. after coming into contact with a lighted cigarette. For this reason, prototypes of all articles which could be a source of danger if they contact with ignition sources should be subjected to the Glow-wire Test.
The ignition source is imitated by an electrically heated wire loop against which the sample is pressed with a constant force. A miniature jacket thermocouple serves as a sensor for the loop temperature.
The sample has to be fastened to a carriage on which, by means of a tensioning cord, a weight
with a force of 1 N is effective in the direction of the wire loop. Scales enable the reading of the flame height and the depth of penetration. Approx. 200 mm below the wire loop a board of pine wood, covered with a layer of tissue paper, is mounted. This device enables to judge the danger of a fire spreading through burning drops or glowing parts falling from the sample.
The specimen and, if necessary, a base shall be attached relative to the wire loop in such a way to represent the most unfavourable practical case. The scales of the measuring device shall be adjusted and the penetration depth of the loop shall be limited by the adjustable stop. After returning and covering the specimen the loop shall be heated up to the specified temperature.
When the loop has maintained the testing temperature for at least 60 seconds, the specimen can be briskly led up to the loop. From the moment of contact, an operation time of exactly 30 seconds must be kept. Then the penetration depth is read and the specimen is slowly returned to its starting position. During and after the operation the burning behaviour of the specimen and the tissue paper on the wooden board has to be observed.