6. Fire Hazard of a Coiled Electric Cord Insulated with Synthetic Rubber

Y. Hagimoto, K. Kinoshita; Summary of 22th Symposium on Safety Engineering, 1992 (I do not know the real name in English.)

Abstracted by translator

Temperature of a coiled cord covered with cloth exceeded 300 C with current of 12.5 Amps. The rubber was carbonised and the cloth started flameless combustion. Electrical energy dissipated in the cord of 200 C is about two times as large as that of 0 C.

Various insulating materials such as chloroprene rubber, neoprene rubber, phenolic resin, uric resin and lauan, a kind of wood, were carbonised in various temperature from 300 to 1000 C. Synthetic rubber showed high conductivity enough to cause short circuit when it was carbonised above 400 C. Other materials carbonised above 700 C showed high conductivity enough to cause short circuit.

These materials were put in a very small case and were heated in a electrical heating box. As they were packed in a very small case, they did not burn and became carbonised in the atmosphere of high temperatures. Low DC voltage was applied to the carbonised material and the DC current flowing through the material was measured. The circuit for this measurement is shown in No. 97. Electrical resistance of the material was calculated from the voltage and the current. figure 2, 3, 4 and 5 shows the relation between the resistance and the current of rubbers, phenolic resin, uric resin and lauan respectively. These figures shows the resistance is low enough to cause an arc discharge if AC 100V is applied to the carbonised materials. If they are used as an insulating material of wiring circuit, they will cause a short circuit.

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