Wire and cable in the process of operation, due to the presence of resistance will heat. Wire resistance is generally very small, its heating power can be expressed by the formula q = I ^ 2R. q = I ^ 2R shows: for a section of the actual use of the wire (R has been basically constant), the greater the current through the wire, the greater the heating power; if the current flow is constant, the heating power of the wire is also constant. In the operation of the heat released will be absorbed by the wire itself, thus causing the wire temperature rise. Wire in the operation process, although constantly in the absorption of current work released heat, but its temperature will not rise indefinitely. Because the wire in the absorption of heat at the same time, but also in the external heat release, the facts show that the conductor is energized after the gradual increase in temperature, and finally the temperature is constant at a certain point. In this constant point, the wire absorbs and releases heat with the same power, the wire is in thermal equilibrium. The ability of the conductor to withstand higher temperatures is a limit, more than a maximum temperature operation will be dangerous. This maximum temperature naturally corresponds to a maximum current, the conductor more than the maximum current operation is overload. Overloading of the conductor directly leads to an increase in the temperature of the conductor itself and of the objects in its vicinity. This increase in temperature is the most direct cause of this type of fire.

　　Overloading the double stranded conductor insulation layer damage caused by a short circuit, burning equipment, causing a fire. Double-stranded wires separated by the insulation layer, overloading the insulation layer softens and destroys, which leads to direct contact between the two strands of wire caused by short-circuit, burn equipment. At the same time short-circuit instantaneous high current generated by the high temperature of the line fire, fusion, resulting in melting beads fall to combustible materials to start a fire. Overload temperature rise can also directly ignite nearby combustible materials. Overloaded wire heat transfer so that the temperature of nearby combustibles rise, the nearby low ignition point of combustibles, it will ignite the fire caused by the fire is possible. In the storage of flammable goods in the warehouse and the use of easy, combustible decoration of the building, this danger is particularly prominent.

　　Overloading also puts the connections in the line under overheating conditions, which accelerates the oxidation process. Oxidation so that the connection point at the production of a thin layer of oxidized film is not easy to conduct electricity, the oxide film increases the resistance between the contact points, thus generating phenomena such as ignition, causing fires.

So, how to prevent fire due to wire and cable overload?

　　1, in the line design process, should be accurately approved the place capacity, give full consideration to the possibility of new capacity in the future, choose the right type of wire. Large capacity, should choose a thicker wire. Line design, reasonable selection is a key step in the prevention of overload. If the design and selection of improper, will leave difficult to rectify the inherent pitfalls. Certain small projects, places do not seriously design selection. Arbitrary selection, laying lines, which is very dangerous. New electrical appliances, electrical equipment should give full consideration to the original line capacity. The original line does not meet the requirements, should be redesigned, remodeling.

　　2, the line should be in accordance with the relevant specification requirements, so that qualified electricians construction laying. Laying conditions of the line directly affects the heat dissipation of the wire. Generally speaking, the line should not be laid through the easy, combustible materials, stacks, which will lead to poor heat dissipation of the wire, heat accumulation, resulting in the possibility of igniting the surrounding combustible items, increasing the risk of fire caused by overload; public entertainment venues should be laid in the ceiling of the line should be protected by wearing a steel pipe in order to make the ceiling and the line isolated, in the case of overloading, short-circuit even if the melting beads will not fall off, to avoid a fire! Occurrence.

　　3、Strengthen the management of electricity, avoid messy wiring, messy lines, careful use of mobile sockets. Messy wiring, messy wiring, the use of mobile sockets is actually in a section of the line to add a power device, increasing the flow of electricity may cause overload. Mobile socket jacks significantly more than the wall of the fixed socket, if the mobile socket on the use of too much electrical equipment, the original line must be difficult to bear. For larger power equipment, electrical appliances should be set up a separate line, should not use the mobile socket as a wiring source.

　　4, to speed up the renewal and transformation of the old lines to eliminate fire hazards. Old enterprises, old neighborhoods and other units, due to the use of time is relatively long, many lines have been aging, more than the use of life. Part of the line even if the load capacity is not large, but the aging line is difficult to withstand such a load capacity, but also has the danger of overloading shown. Especially in old residential areas, the line has long been aging, but with the improvement of people's living standards, the increase in household appliances, its electricity consumption is still rising year by year, really adding insult to injury. For the old lines, should be timely supervision, coordination, as soon as possible to urge its rectification, in order to eliminate fire hazards, to ensure safety.