Short circuit. The so-called short circuit is the exchange of two conductors of the circuit touch each other, the current does not go through the line of electrical equipment, and the formation of the loop. As the resistance of the wire itself is relatively small, if only through the circuit of this wire, the current will increase sharply, than the normal case of a few times, hundreds of times. With such a large current flowing through such a thin wire, the greater the resistance, the more heat is generated, causing the wire to produce temperatures as high as several thousand degrees Celsius in a very short time enough to ignite flammable materials in the vicinity, causing Fire. Short circuit caused by the line is due to the transmission line used for too long, insulation aging, rupture, loss of insulation, leading to collision of two lines; or chaotic pull the wire, the wire "jacket" mechanical damage, causing a short circuit.