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Short circuit

From Academic Kids

For alternate meanings see Short circuit (disambiguation)

A short circuit (sometimes known as simply a short) is a fault whereby electricity moves through a circuit in an unintended path, usually due to a connection forming where none was expected. This unintended path often has a very low resistance which means that a much larger current than normal flows, potentially causing overheating, fire or explosion.

The simplest way to cause a short circuit is to connect the positive and negative ends of a battery together with a low-resistance conductor, like a wire. With low resistance in the connection, high current is generated, causing the cell to output a large amount of energy in a short time. (See also: Ohm's law, power) Caution: Actually performing this experiment could result in the rapid buildup of heat, damage to the wire or cell, a release of toxic fumes, and/or an explosion of the battery. Do not attempt this.

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

A large current through a battery (also called a cell) can cause the rapid buildup of heat, potentially resulting in an explosion or the release of hydrogen gas and electrolyte, which can burn tissue and may be either an acid or a base. Overloaded wires can also overheat, sometimes causing damage or fire to the wire's insulation. High current conditions may also occur with electric motor loads under stalled conditions, such as when the impeller of an electrically driven pump is jammed by some debris.

Damage from short circuits can be reduced or prevented by employing fuses, circuit breakers, or other overload protection, which disconnect the power in reaction to excessive current. Overload protection must be chosen having regard for the maximum prospective short circuit current in a circuit. Wire sizes are specified in building and electrical codes, and must be carefully chosen for their specific application to ensure safe operation in conjunction with the overload protection.

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 flowing and therefore quickly trigger an overcurrent 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 flowing and are therefore less likely to be detected. Possible effects include unexpected energisation of a circuit presumed to be isolated.

The electrical opposite of a short circuit (zero resistance between input voltage and ground) is an open circuit (infinite resistance between input voltage and ground).

It is common for people to incorrectly use "short circuit" to describe any electrical malfunction, regardless of the actual problem.

On occasion, short circuits are instigated intentionally, usually for the purpose of circuit bending.

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