In the process of operation, wires and cables will be heated due to the existence of resistance. Generally, the resistance of the conductor is very small, and its heating power can be expressed by the formula q = I ^ 2R. Q = I ^ 2R shows that for a section of conductor in actual use (r has been basically constant), the greater the current passing through the conductor, the greater the heating power; if the electric flow is constant, the heating power of the conductor is also constant. The heat released during operation will be absorbed by the conductor itself, which will cause the conductor temperature to rise. Although the conductor is constantly absorbing the heat released by the work done by the current during the operation, its temperature will not rise unrestricted. Because the conductor is absorbing heat and releasing heat to the outside, the fact shows that the temperature of the conductor rises gradually after being electrified, and the temperature is constant at a certain point after Zui. At this constant point, the heat absorbing and releasing power of the conductor are the same, and the conductor is in the state of heat balance. The ability of the conductor to withstand high temperature operation is limited, and exceeding a certain Zui high temperature operation will cause danger. The high temperature of this Zui naturally corresponds to a certain Zui current. If the conductor exceeds this Zui current, it is overloaded. The overload of the conductor directly causes the temperature of the conductor itself and its nearby objects to rise. The temperature rise is the direct cause of this kind of fire.
Overload leads to the damage of insulation layer between two strands of wires, causing short circuit, burning equipment and fire. The double wires are separated by the insulating layer between them, and the overload makes the insulating layer soften and damage, which leads to the direct contact between the two wires, causing 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 fire and fuse, and the molten bead produced falls to the combustible to cause the fire. Overload temperature rise can also directly ignite nearby combustibles. It is possible for the combustibles with lower ignition point to ignite and cause fire. This kind of danger is especially prominent in the storehouse where inflammable materials are stored and in the buildings which are easy to use and combustible to decorate.
Overload also makes the connection in the circuit overheat, which accelerates its oxidation process. Oxidation causes a thin layer of oxide film which 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 fire.
So, how to prevent the fire caused by overload of wires and cables?
1. In the process of line design, the capacity of the site should be accurately verified, the possibility of new capacity in the future should be fully considered, and the appropriate type of conductor should be selected. The larger capacity, the thicker conductor should be selected. Line design and reasonable selection are the key steps to prevent overload. If the design and selection are improper, it will leave a congenital hidden danger that is difficult to rectify. Some small projects and places are not carefully designed and selected. It is very dangerous to choose and lay lines at will. The bearing capacity of the original circuit shall be fully considered for new electrical appliances and electric equipment. If the original line does not meet the requirements, it shall be redesigned and reconstructed.
2. The line shall be laid by electricians in accordance with relevant specifications. The laying conditions of the line directly affect the heat dissipation of the conductor. Generally speaking, the laying of the line should not pass through easy, combustible materials and stacking, which will lead to poor heat dissipation and heat accumulation of the wire, the possibility of igniting combustible materials around, and increase the risk of fire under overload; The lines laid in the ceiling of public entertainment places shall be protected by steel pipes to separate the ceiling from the lines. In case of overload and short circuit, even if there are molten beads, they will not fall to avoid fire.
3. Strengthen the management of electricity use, avoid disorderly wiring and grounding, and use mobile socket carefully. Disorderly wiring, disorderly grounding and use of mobile socket are actually adding electrical equipment to a certain line, increasing the amount of current and possibly causing overload. The mobile socket jack is obviously more than the fixed socket on the wall. If too much electrical equipment is used on the mobile socket, the original line will be difficult to bear. For equipment and electrical appliances with high power, separate lines should be set, and mobile sockets should not be used as wiring sources.
4. Speed up the renovation of old lines and eliminate fire hazards. Old enterprises, old residential areas and other units, due to the long service life, many lines have been aging, beyond the service life. Even though the current carrying capacity of some lines is not large, the aging lines are also difficult to bear such current carrying capacity, which also has the danger of overload. Especially in the old residential areas, the lines have been aging for a long time, but with the improvement of people's living standards and the increase of household appliances, the power consumption is still rising year by year. For old lines, timely supervision and coordination should be carried out to promote their rectification as soon as possible, so as to eliminate fire hazards and ensure safety.
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