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Wire and cable in the course of operation, due to the presence of resistance will be hot. The resistance of the conductor is generally very small, its heating power can be expressed by formula Q=I^2R. Q=I^2R shows that: for a section of the actual use of the Wire (R has been basically constant), the more current through the wire, the greater the heating power; If the electrical flow is constant, the heating power of the conductor is also constant. The heat emitted during the operation is absorbed by the conductor itself, causing the lead temperature to rise. While the conductor is in the process of absorbing the current to work out the heat release, but its temperature will not increase without limit. Because the wire in the endothermic, but also continuously to the outside heat, the fact that the wire after the temperature gradually rise, the final temperature is constant at a certain point. At this constant point, the wire absorbs and radiates power uniformly, and the conductor is in a thermal equilibrium state. There is a limit to the ability of the conductor to operate at a higher temperature, and it is dangerous to run above a certain maximum temperature. This maximum temperature naturally corresponds to a maximum current, which is overloaded when the conductor exceeds this maximum current. The conductor overload leads directly to the temperature of the conductor itself and its nearby objects. Temperature rise is the most direct cause of this type of fire.
Overload causes the insulating layer between the two strands to cause short-circuit, burn the equipment, and cause a fire. The two-strand conductor is separated by insulating layer, overload causes the insulating layer to soften and destroy, thus causes the two strands direct contact to cause the short circuit, the burning loss equipment. At the same time short-circuit instantaneous high temperature caused by the circuit fire, fuse, the resulting bead fell to the combustible fire caused. Overload temperature rise can also directly ignite nearby combustible material. The heat transfer of overload conductor causes the ambient combustible temperature to rise, and it is possible to ignite the combustible material near the ignition point. In the storage of flammable materials and the use of easy, combustible decoration of the building, this danger is particularly prominent.
Overload also causes the connection in the line to overheat, which accelerates the oxidation process. Oxidation makes the junction point of a thin layer of oxide film that is not conductive, the oxide film increases the resistance between contact points, thus creating a spark and other phenomena, causing fire.
So how do you prevent a fire from overloading the wire and cable?
1, in line design process, should accurately approve the site capacity, fully consider the possibility of new capacity, select the appropriate type of wire. Large capacity, thicker wire should be selected. Line design, reasonable selection is the key step to prevent overload. If the design of improper selection, will leave difficult to rectify the congenital hidden danger. Some small projects, places do not carefully design selection. It is very dangerous to choose and lay the line randomly. New appliances, electrical equipment should be fully considered the original line to withstand capacity. The original line does not meet the requirements, should be redesigned, modified.
2, the line should be in accordance with the relevant specifications, so that the electrician qualified personnel to lay the construction. The laying condition of the line directly affects the heat dissipation of the conductor. Generally speaking, line laying should not cross the easy, combustible material, stacking, this will lead to poor cooling of the conductor, heat accumulation, the possibility of igniting combustible goods around the ignition, increased the risk of fire caused by overload; public places of entertainment decorate the ceiling should wear steel pipe protection, so that the ceiling and line separated, in overload, Short circuit and so on, even if there is no melting bead will not fall, to avoid fire.
3, strengthen power management, avoid disorderly wiring, disorderly lap line, use mobile socket carefully. Disorderly wiring, disorderly lap line, the use of mobile sockets is actually in a certain section of the line to add electrical equipment, increased the flow of electricity may cause overload. Mobile socket Jack significantly more than the wall of fixed sockets, if the mobile socket on the use of excessive electrical equipment, the original line must be unbearable. For the higher power equipment, electrical appliances should be set up a separate line, it is inappropriate to use mobile sockets as the wiring source.
4, speed up the old line of the renovation, eliminate fire hazards. Old enterprises, old residential areas and other units, due to the use of a long time, many lines have been aging, more than the service life. Some lines of the load flow even if not small, but the aging line is difficult to withstand such load flow, but also has the danger of overload. In particular, the old residential areas, the line has long been aging, but with the improvement of people's living standards, household appliances, the increase in electricity consumption is still rising year by quarter, really worse. For the old line, should be timely supervision, coordination, as soon as possible to promote its rectification, to eliminate fire hazards, to ensure safety.