Editing Ground (electricity) (section)

== Isolation ==
{{See also|Galvanic isolation}}

Isolation is a mechanism that defeats grounding. It is frequently used with low-power consumer devices, and when engineers, hobbyists, or repairmen are working on circuits that would normally be operated using the power line voltage. Isolation can be accomplished by simply placing a "1:1 wire ratio" transformer with an equal number of turns between the device and the regular power service, but applies to any type of transformer using two or more coils electrically insulated from each other.

For an isolated device, touching a single powered conductor does not cause a severe shock, because there is no path back to the other conductor through the ground. However, shocks and electrocution may still occur if both poles of the transformer are contacted by bare skin. Previously it was suggested that repairmen "work with one hand behind their back" to avoid touching two parts of the device under test at the same time, thereby preventing a current from crossing through the chest and interrupting cardiac rhythms or causing [[cardiac arrest]].<ref name= electricalSafety >{{Cite web |title=Physiological Effects of Electricity |work=Electrical Safety, Direct Current (DC) |publisher=All About Circuits |first1=Tony R. |last1=Kuphaldt |url=https://www.allaboutcircuits.com/textbook/direct-current/chpt-3/physiological-effects-electricity/ |url-status=live |archive-url=https://web.archive.org/web/20240225214454/https://www.allaboutcircuits.com/textbook/direct-current/chpt-3/physiological-effects-electricity/ |archive-date=Feb 25, 2024}}</ref>

Generally every AC power line transformer acts as an isolation transformer, and every step up or down has the potential to form an isolated circuit. However, this isolation would prevent failed devices from blowing fuses when shorted to their ground conductor. The isolation that could be created by each transformer is defeated by always having one leg of the transformers grounded, on both sides of the input and output transformer coils. Power lines also typically ground one specific wire at every pole, to ensure current equalization from pole to pole if a short to ground is occurring.

In the past, grounded appliances have been designed with internal isolation to a degree that allowed the simple disconnection of ground by [[cheater plug]]s without apparent problem (a dangerous practice, since the safety of the resulting floating equipment relies on the insulation in its power transformer). Modern appliances however often include [[power entry module]]s which are designed with deliberate capacitive coupling between the AC power lines and chassis, to suppress electromagnetic interference. This results in a significant leakage current from the power lines to ground. If the ground is disconnected by a cheater plug or by accident, the resulting leakage current can cause mild shocks, even without any fault in the equipment.<ref>{{cite web|url=http://news.cnet.com/8301-17938_105-9852716-1.html|title=Dell laptops in electric-shock shocker|date=17 January 2008|website=CNET |agency=Crave |first1=Rory |last1=Reid |url-status=dead |archive-url=https://web.archive.org/web/20140208184052/http://news.cnet.com/8301-17938_105-9852716-1.html|archive-date=8 February 2014}}</ref> Even small leakage currents are a significant concern in medical settings, as the accidental disconnection of ground can introduce these currents into sensitive parts of the human body. As a result, medical power supplies are designed to have low capacitance.<ref>{{cite web |url=http://www.slpower.com/reference/An113%20Leakage%20Current.pdf |title=Leakage Current |id=AN-113 |publisher=Condor |via=SL Power Electronics |access-date=2013-08-22 |url-status=dead |archive-url=https://web.archive.org/web/20150501203234/http://www.slpower.com/reference/An113%20Leakage%20Current.pdf |archive-date=2015-05-01 }}</ref>

[[Appliance classes|Class II]] appliances and power supplies (such as cell phone chargers) do not provide any ground connection, and are designed to isolate the output from input. Safety is ensured by double-insulation, so that two failures of insulation are required to cause a shock.