A short circuit occurs when the live and neutral conductors in a circuit make unintended contact, creating a path of very low resistance that allows a large surge of current to flow. The circuit breaker protecting that circuit responds by tripping almost instantly.
Unlike an overload — where current increases gradually as more appliances draw power — a short circuit typically causes an immediate and complete loss of power to the circuit, often the moment a particular appliance is switched on or a cable is disturbed. Common causes include cable insulation that has deteriorated or been physically damaged, a failed internal connection within a socket, switch, or light fitting, a faulty appliance with damaged internal wiring, and mechanical damage to a hidden cable — for example, where a nail or screw has been driven through a cable during building work or DIY alterations.
Before an electrician visits, switch off the tripped breaker and note whether the trip happened when a specific appliance was turned on. If you suspect a particular appliance, unplugging it before the electrician arrives allows testing to begin with the circuit clear of connected equipment.
Do not attempt to trace cable routes by probing walls or removing fixings yourself. To locate a short circuit, the electrician de-energises the circuit and uses insulation resistance test equipment to confirm whether the fault is in the fixed wiring or a fitting.
Progressive isolation — disconnecting sections of the circuit in turn — narrows down the fault location. Where the fault is in a cable, the damaged section is repaired or replaced.
Where a fitting is the source, it is replaced and the surrounding cable integrity checked before the circuit is tested and restored to use.