Editing Short circuit

{{Short description|Electrical circuit with negligible impedance}}
{{Other uses}}
{{more citations needed|date=July 2019}}[[File:Crossed wires.JPG|thumb|Tree limbs cause a short circuit, triggering an [[electrical arc]] during a storm.]]

A '''short circuit''' (sometimes abbreviated to '''short''' or '''s/c''') is an [[electrical network|electrical circuit]] that allows a [[Electric current|current]] to travel along an unintended path with no or very low [[electrical impedance]]. This results in an excessive current flowing through the circuit.
The opposite of a short circuit is an '''open circuit''', which is an infinite [[Electrical resistance and conductance|resistance]] (or very [[high impedance]]) between two nodes.

== Definition ==
A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different [[voltage]]s. This results in an [[electric current]] limited only by the [[Thévenin's theorem|Thévenin equivalent resistance]] of the rest of the network which can cause circuit damage, [[Overheating (electricity)|overheating]], [[fire]] or [[explosion]]. Although usually the result of a [[Electrical fault|fault]], there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensing [[Crowbar (circuit)|crowbar circuit protectors]].

In [[circuit analysis]], a ''short 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.

== Examples ==
A common type of short circuit occurs when the positive and negative terminals of a [[Battery (electricity)|battery]] or a [[capacitor]] are connected with a low-[[electrical resistance|resistance]] [[Electrical conductor|conductor]], like a [[wire]].  With a low resistance in the connection, a high [[Current (electricity)|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 of [[hydrogen]] gas and [[electrolyte]] (an [[acid]] or a [[base (chemistry)|base]]), which can burn tissue and cause blindness or even death. Overloaded wires will also [[Overheating (electricity)|overheat]] causing damage to the wire's insulation, or starting a fire. 

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

In [[Mains electricity|mains]] circuits, short circuits may occur between two [[Polyphase system|phases]], between a phase and [[Ground and neutral|neutral]] or between a phase and [[Ground and neutral|earth]] (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 of [[Leakage inductance|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]].
[[File:Melting an iron nail.webm|thumb|Short-circuiting a 3000 [[farad]] [[supercapacitor]] through an iron nail resulted in a 1000 [[amperes]] current. This caused the iron nail to melt, eject [[Spark (fire)|sparks]], and eventually break, becoming an open circuit.]]
A short circuit may lead to formation of an [[electric arc]]. The arc, a channel of hot ionized [[plasma (physics)|plasma]], is highly conductive and can persist even after significant amounts of original material from the conductors has 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.<ref>{{cite web | title = Lab Note #105 ''Contact Life - Unsuppressed vs. Suppressed Arcing'' | publisher = Arc Suppression Technologies | date = April 2011 | url = http://www.arcsuppressiontechnologies.com/arc-suppression-facts/lab-app-notes/ | access-date = February 5, 2012 | archive-date = September 30, 2018 | archive-url = https://web.archive.org/web/20180930071357/http://www.arcsuppressiontechnologies.com/arc-suppression-facts/lab-app-notes/ | url-status = live }}</ref>

== Damage ==
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.<ref name="pdh">{{cite web |url=https://www.pdhonline.com/courses/e204/e204content.pdf |title=Introduction to Short Circuit Analysis |website=PDHonline |last=Bhatia |first=A. |access-date=3 July 2019 |at=sec. What causes a short circuit? |archive-date=3 July 2019 |archive-url=https://web.archive.org/web/20190703040023/https://www.pdhonline.com/courses/e204/e204content.pdf |url-status=live}}
*{{cite web |last=Bhatia |first=A. |title=Introduction to Short Circuit Analysis |type=Synopsis |url=https://www.pdhonline.com/courses/e204/e204.htm |website=PDHonline}}</ref> Damage from short circuits can be reduced or prevented by employing [[Fuse (electrical)|fuses]], [[circuit breaker]]s, or other [[overload 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 large [[home appliance]]s  require protective devices set or rated for higher currents than lighting circuits. [[Wire gauge]]s specified in building and electrical [[building code|codes]] are chosen to ensure safe operation in conjunction with the overload protection. An overcurrent protection device must be rated to safely interrupt the maximum [[prospective short-circuit current]].

In an improper installation, the overcurrent from a short circuit may cause [[ohmic 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 (electricity)|overheating]] is a common cause of [[fire]]s. 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.

== Related concepts ==
In [[electronics]], the ideal model (infinite [[Gain (electronics)|gain]]) of an [[operational amplifier]] is said to produce a ''virtual short circuit'' between its input terminals because no matter what the output voltage is, the [[difference 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 a [[virtual ground]] because its potential is (ideally) identical to that of the ground.<ref>{{cite book |title=Basic Electronics |date=March 2011 |url=https://books.google.com/books?id=_zytO-iXdxUC&pg=PA184 |access-date=20 April 2011 |publisher=I. K. International Pvt Ltd |pages=184– |id=GGKEY:9NLKFQ9D0F2 |archive-date=2 May 2013 |archive-url=https://web.archive.org/web/20130502181149/http://books.google.com/books?id=_zytO-iXdxUC&pg=PA184 |url-status=live }}</ref><ref>{{cite book |author=Robert Spence |title=Introductory Circuits |url=https://books.google.com/books?id=mTnCz_zYmWsC&pg=PT99 |access-date=20 April 2011 |date=5 September 2008 |publisher=John Wiley and Sons |isbn=978-0-470-77971-2 |pages=99– |archive-date=2 May 2013 |archive-url=https://web.archive.org/web/20130502174336/http://books.google.com/books?id=mTnCz_zYmWsC&pg=PT99 |url-status=live }}</ref> An ideal operational amplifier also has infinite [[input impedance]], so unlike a real short circuit, no current flows between the terminals of the virtual short.<ref>{{cite book |author1=U.A.Bakshi |author2=A.P.Godse |title=Linear Integrated Circuits |url=https://books.google.com/books?id=-zAe0P33BAcC&pg=SA4-PA2 |access-date=20 April 2011 |date=1 January 2010 |publisher=Technical Publications |isbn=978-81-8431-773-2 |pages=4– }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

== See also ==
{{Portal|Electronics}}
* [[Annealing by short circuit]]
* [[Breaking capacity]]
* [[Conditional short-circuit current]]
* [[Short-circuit test]]
* Other [[electrical fault]]s:
** [[Ground fault]]
* [[Ohm's law]]
* [[Overcurrent]], electrical overload

==References==
{{Reflist}}

==External links==
*{{Wiktionary-inline|short circuit}}
*{{Commons category-inline}}
* [http://www.thecircuitdetective.com/locate_electrical_fault.php#shor Troubleshooting Strategy for US/Canadian Homes] from The Circuit Detective

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[[Category:Electricity]]
[[Category:Electrical engineering]]
[[Category:Safety]]
[[Category:Fire prevention]]
[[Category:Fire protection]]