Editing Double switching (section)

[[image:Single switching.svg|frame|right|A single-switched relay can close inadvertently in response to a single false feed current.]]
[[image:Double switched.svg|frame|right|A double-switched relay cannot close inadvertently with the application of the same current. At least two separate faults would be required to allow this relay to close inadvertently.]]

'''Double switching''', '''double cutting''', or '''double breaking''' is the practice of using a multipole [[switch]] to close or open both the positive and negative sides of a [[Direct current|DC]] [[electrical circuit]], or both the hot and neutral sides of an [[Alternating current|AC]] circuit. This technique is used to prevent [[Electric shock|shock hazard]] in electric devices connected with unpolarised [[AC power plugs and sockets]]. Double switching is a crucial safety engineering practice in [[railway signalling]], wherein it is used to ensure that a single false feed of [[electric current|current]] to a [[relay]] is unlikely to cause a [[wrong-side failure]]. It is an example of using [[Redundancy (engineering)|redundancy]] to increase safety and reduce the likelihood of failure, analogous to [[double insulated|double insulation]]. Double switching increases the cost and complexity of systems in which it is employed, for example by extra relay contacts and extra relays, so the technique is applied selectively where it can provide a cost-effective safety improvement.