The Influence Of Current Overload On Wires And Cables

During the use of the wire and cable, heat will be generated due to the existence of resistance. Overloading may cause excessive heat to gather together, which may cause a fire. The resistance of wire and cable is generally very small, and its heating power can be expressed by the formula q=I^2R. q=I^2R indicates that: for a piece of wire and cable in actual use (R is basically constant), the greater 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 will be absorbed by the wire and 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 of the current during operation, their temperature will not rise indefinitely. Because the wires and cables are absorbing heat, they are also constantly radiating heat to the outside world. The facts show that the temperature of the wires and cables gradually rises after being energized, and finally the temperature is constant at a certain point. At this constant point, the heat absorption and heat dissipation power of the wire and cable are the same, and the wire and cable are in a state of thermal equilibrium. The ability of wires and cables to withstand higher temperature operation is limited, and operation exceeding a certain maximum temperature will be dangerous. This maximum temperature naturally corresponds to a certain maximum current. Wires and cables running beyond this maximum current are overloaded. Overloading of wires and cables directly causes the temperature of the wires and cables themselves and their nearby objects to increase. The increase in temperature is the most direct cause of this type of fire. .

Overload damages the insulation layer between the double-stranded wires and cables, causing a short circuit, burning the equipment, and causing a fire. The double-stranded wires and cables are separated by the insulating layer between them. Overloading softens and destroys the insulating layer, which leads to direct contact between the two wires and cables, causing a short circuit and burning equipment. At the same time, the high temperature generated by the large current at the moment of short-circuit causes the line to catch fire and fuse, and the resulting molten beads fall to combustibles and cause a fire. The increase in overload temperature can also directly ignite nearby combustibles. The heat transfer of overloaded wires and cables will increase the temperature of nearby combustibles. For nearby combustibles with low ignition point, it is possible to ignite them and cause a fire. This danger is particularly prominent in warehouses that store flammable materials and buildings that are easy to use and combustible decorations.

Overload also puts the connections in the line under overheating conditions, which accelerates the oxidation process. Oxidation produces a thin layer of oxide film that is not easy to conduct electricity at the connection point. The oxide film increases the resistance between the contact points, resulting in ignition and other phenomena, causing a fire.

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