A short circuit occurs when current flows along an unintended low-resistance path between conductors that should not be in contact. The most common form involves a live conductor touching a neutral conductor, causing a sudden large surge of current.
The circuit breaker or fuse on that circuit responds by disconnecting it, which prevents sustained damage to the wiring. Although the protective device is working correctly, the underlying fault must be identified and repaired before the circuit can be returned to service.
Short circuits are caused by a range of factors. Damaged cable insulation that allows conductors to touch is a common cause, as are loose connections at sockets, switches, light fittings or junction boxes where conductors have worked free over time.
Physical damage to cables from screws or nails inserted through walls or floors can also create a short circuit by breaching the insulation. In some cases, the fault originates within a connected appliance rather than in the fixed wiring.
Identifying the precise location of a short circuit requires systematic testing of the affected circuit. The engineer isolates sections of wiring and accessories in sequence, measuring insulation resistance between conductors, until the fault is localised to a specific section of cable or a particular fitting.
The repair then involves replacing the damaged cable section, re-making connections that have failed, or replacing a faulty accessory. Where a cable fault extends across a significant length of circuit, a partial rewire of that run may be the most appropriate solution.
Once repaired, the circuit is re-tested to confirm that insulation resistance and continuity values meet the requirements of BS 7671 before it is returned to service. If you suspect a short circuit, leave the affected circuit off where it can be isolated safely.
Do not touch hot or damaged controls, open the consumer unit or repeatedly reset protection. For fire or smoke suggesting one, get out, stay out and call 999.
Engineers covering Poole and the surrounding area can be contacted through this site to arrange a diagnosis and repair.