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Ashort circuit (sometimes abbreviated to "short" or "s/c") is anelectrical circuit that allows anelectric current to travel along an unintended path with no or very lowelectrical impedance. This results in an excessive current flowing through the circuit.
The opposite of a short circuit is anopen circuit, which is an infiniteresistance (or veryhigh impedance) between two nodes.
A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at differentvoltages. This results in a current limited only by theThévenin equivalent resistance of the rest of the network which can cause circuit damage,overheating,fire orexplosion. Although usually the result of afault, there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensingcrowbar circuit protectors.
Incircuit analysis, ashort circuit is defined as a connection between two nodes that forces them to be at the same voltage. In an 'ideal' short circuit, this means there is no resistance and thus no voltage drop across the connection. In real circuits, the result is a connection with almost no resistance. In such a case, the current is limited only by the resistance of the rest of the circuit.
A common type of short circuit occurs when the positive and negative terminals of abattery or acapacitor are connected with a low-resistanceconductor, like awire. With a low resistance in the connection, a high current will flow, causing the delivery of a large amount of energy in a short period of time.
A high current flowing through a battery can cause a rapid increase of temperature, potentially resulting in an explosion with the release ofhydrogen gas andelectrolyte (anacid or abase), which can burn tissue and cause blindness or even death. Overloaded wires will also overheat causing damage to the wire's insulation, or starting a fire.
In electrical devices, unintentional short circuits are usually caused when a wire'sinsulation breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended.
Inmains circuits, short circuits may occur between twophases, between a phase andneutral or between a phase andearth (ground). Such short circuits are likely to result in a very high current 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 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 ofleakage 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.
A short circuit may lead to formation of anelectric arc. The arc, a channel of hot ionizedplasma, is highly conductive and can persist even after significant amounts of original material from the conductors have evaporated. Surface erosion is a typical sign of electric arc damage. Even short arcs can remove significant amounts of material from the electrodes. The temperature of the resulting electrical arc is very high (tens of thousands of degrees), causing the metal on the contact surfaces to melt, pool and migrate with the current, as well as to escape into the air as fine particulate matter.[1]
Within milliseconds, a short circuit can deliver a fault current that is hundreds or thousands of times higher than the normal operating current of the system.[2]
In an improper installation, theovercurrent from a short circuit may causeohmic heating of the circuit parts with poor conductivity (faulty joints in wiring, faulty contacts in power sockets, or even the site of the short circuit itself). Such overheating is a common cause offires. An electric arc, if it forms during the short circuit, produces high amount of heat and can cause ignition of combustible substances as well.
In industrial and utility distribution systems, dynamic forces generated by high short-circuit currents cause conductors to spread apart. Busbars, cables, and apparatus can be damaged by the forces generated in a short circuit.
Damage from short circuits can be reduced or prevented by employingfuses,circuit breakers, or otheroverload protection, which disconnect the power in reaction to excessive current. Overload protection must be chosen according to the current rating of the circuit. Circuits for largehome appliances require protective devices set or rated for higher currents than lighting circuits.Wire gauges specified in building and electricalcodes are chosen to ensure safe operation in conjunction with the overload protection. An overcurrent protection device must be rated to safely interrupt the maximumprospective short-circuit current.
Inelectronics, the ideal model (infinitegain) of anoperational amplifier is said to produce avirtual short circuit between its input terminals because no matter what the output voltage is, thedifference of potential between its input terminals is zero. If one of the input terminals is connected to the ground, then the other one is said to provide avirtual ground because its potential is (ideally) identical to that of the ground.[3][4] An ideal operational amplifier also has infiniteinput impedance, so unlike a real short circuit, no current flows between the terminals of the virtual short.[5]
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