The main cause of a short circuit is when two bare wires touch each other. This causes extra current to flow through the circuit, which can be dangerous. Two bare wires typically come into contact with each other when the insulation around the wires deteriorates.
Short circuits can occur in both AC and DC circuits and typically result in a blown fuse or a tripped breaker. Because of the increased amount of energy flowing through the circuit, it also becomes hot, which can cause fires. Fuses, or circuit breakers, are designed to prevent this, as long as they are installed correctly.
In addition to touching wires and deteriorated insulation, there are other things that sometimes cause a short circuit. These include faulty or poorly installed wiring that causes the wires to touch each other, overloading the circuit and faulty units including switches, plugs and cords.
When a circuit shorts, it is important to locate the source. This can be done by resetting the breaker and trying to trace the short circuit back to the switch, receptacle or electrical appliance. For example, if the breaker trips once a particular electrical appliance is turned on, the short circuit is likely to be in that appliance. All switches and appliances should be turned off before attempting to locate the faulty circuit.