(1) overload. Refers to the electrical equipment or wire power or current exceeds its rating. The main hazard of overloading faults is that the conductor converts the electrical energy into heat energy under the condition of overload so that the conductor and its insulation partially overheat. When the required temperature is reached, it can ignite nearby combustibles and form a fire. .

(2) short circuit. Electrical circuit When a short circuit occurs, the electrical circuit branch load will be cut off, the current and load impedance is inversely proportional to the change When the impedance tends to be small, the current tends to be very, so the heat generated is very good at this time if the insurance can not be instantaneous Disconnect, then the wire will fire, resulting in a fire.

(3) contact resistance. Electrical circuit lap, and then contact the contact loose, the voltage between the contacts enough to break through the gap air, the formation of air conduction, if the contact point slightly larger, and coincident peak power supply voltage fluctuations, the arc will be pulled out in the air, light The nearby combustible material creates a fire.