Electrical fault

An electrical fault is a problem with an electronic device that causes electrical current to flow incorrectly.

The best known type of electrical fault is a short circuit, where current flows between two places where it should not. "Short circuit" is often used improperly to mean any kind of electrical fault. Short circuits and open circuits, where current does not flow between two places where it should, are the simplest types of electrical fault.

Types of fault

Closed versus open

Many electrical faults can be categorised as closed circuit faults and open circuit faults. In a closed circuit fault, current flows between parts of the circuit where it should not; in an open circuit fault, it does not flow between parts of the circuit where it should. These types of fault don't care about how much current there is, just whether it is flowing and in what direction.

The simplest open circuit fault is caused by physical damage to a conductor, like a broken wire. They can also be caused by problems in manufacturing components. The term "open circuit" is normally only used for a full disconnection: a decrease in current, such as a high resistance connection, is not an open circuit fault.

The simplest example of a closed circuit fault is a short circuit, where the two connected points are treated as having (nearly) zero electrical resistance, usually because a piece of conductor is connecting them. Another common closed circuit fault that is not a short circuit is caused by a diode exceeding its breakdown voltage.

Transient versus persistent

An electrical fault that can be resolved by disconnecting power from the system and then reconnecting it is called a transient fault. If a fault is not transient, it is persistent.

An example of a transient fault is caused when lightning strikes near a power line. The electromagnetic induction from the strike can disrupt power transmission, but does not physically damage the cables. Disconnecting and reconnecting the cable with circuit breakers allows transmission to resume. If the cable is instead damaged by falling debris, it creates a persistent fault which must be repaired.