Question

What is SHORT CIRCUIT and how may a short circuit develop

A short circuit is an abnormal low-resistance connection between two nodes of an electrical circuit that are meant to be at different voltages.

In electrical devices, unintentional short circuits are usually caused when a wire's insulation breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended.

In mains circuits, short circuits are most likely to occur between two phases, between a phase and neutral or between a phase and earth (ground).

Such short circuits are likely to result in a very high current and therefore quickly trigger an over current protection device.

However, it is possible for short circuits to arise between neutral and earth conductors, and between two conductors of the same phase.

Such short circuits can be dangerous, particularly as they may not immediately result in a large current and are therefore less likely to be detected. Possible effects include unexpected energisation of a circuit presumed to be isolated.

To help reduce the negative effects of short circuits, power distribution transformers are deliberately designed to have a certain amount of leakage reactance.

The leakage reactance (usually about 5 to 10% of the full load impedance) helps limit both the magnitude and rate of rise of the fault current.