Is overloading the wires and cables causing a fire?

- Oct 11, 2019-

During the use of wires and cables, heat is generated due to the presence of electrical resistance. Overloading can cause too much heat to get together and can cause a fire.

The resistance of wires and cables is generally small, and the heating power can be expressed by the formula q=I^2R. q=I^2R indicates: For a wire and cable in actual use (R is almost constant), the larger the current through the wire and cable, the greater the heating power; if the current is constant, the heating power of the wire and cable It is also constant. The heat released during operation is absorbed by the wire cable itself, causing the temperature of the wire and cable to rise. Although the wire and cable are constantly absorbing the heat released by the work during the operation, the temperature of the wire and cable does not rise without limit. Because the wire and cable absorb heat while constantly venting heat to the outside world, the facts show that the temperature of the wire and cable is gradually increased after the power is applied, and finally the temperature is constant at a certain point. At this constant point, the wire and cable have the same heat absorption and heat release, and the wire and cable are in thermal equilibrium. The ability of wire and cable to withstand higher temperatures is limited, and operation above a certain maximum temperature can be dangerous. This maximum temperature naturally corresponds to a certain maximum current. When the wire and cable exceeds this maximum current, it is overloaded. The overload of the wire and cable directly causes the temperature of the wire and cable itself and its nearby objects to rise. The temperature rise is the most direct cause of such fires. .

The overload causes the insulation of the double-strand wire and cable to break, causing a short circuit, burning the equipment and causing a fire. The double-strand electric wire and cable are separated by the insulating layer therebetween, and the overload causes the insulating layer to soften and break, thereby causing direct contact between the two wires and cables to cause a short circuit and burning the device. At the same time, the high temperature generated by the large current at the moment of short circuit causes the line to ignite and melt, and the generated beads fall to the combustibles to cause a fire. The increase in overload temperature can also directly ignite nearby combustibles. The heat transfer of the overloaded wires and cables can increase the temperature of nearby combustibles. It is possible to ignite and ignite the combustibles with low ignition points nearby. This hazard is particularly acute in warehouses where flammable materials are stored and in buildings that are easy to use and flammable.

Overloading also places the connections in the line under overheating conditions, which accelerates the oxidation process. Oxidation causes a thin oxide film that is not easily conductive at the joint, and the oxide film increases the electric resistance between the contact points, thereby causing a phenomenon such as sparking and causing a fire.