Editing Appliance classes (section)

==Class I==
[[File:Color wire green yellow.svg|thumb|left|upright=0.5|Green ground wire with yellow stripe]]
[[File:Schutzklasse 1.svg|thumb|upright=0.5|Symbol used to mark the Protective Earthing Conductor terminal of Class I equipment]]

Appliance class I is not only based on the basic insulation, but the casing and other conductive parts are also connected with a low-resistant earth conductor. Hence, these appliances must have their chassis connected to [[Ground (electricity)|electrical earth]] (US: ground) by a separate [[Earth (electricity)|earth]] conductor ([[IEC 60446|coloured]] green/yellow in most countries, green in India, USA, Canada and Japan). The earth connection is achieved with a three-conductor mains cable, typically ending with three-prong [[AC connector]] which plugs into a corresponding AC outlet. 

Plugs are designed such that the connection to the protective earth conductor should be the first connection when plugged in. It should also be the last to be broken when the plug is removed.<ref name="ESDBook">{{Cite book|author=J. Lienig|author2=H. Bruemmer|title=Fundamentals of Electronic Systems Design|pages=40–41|chapter=Sec. 3.4.2 Protection Classes|publisher=Springer International Publishing|date=2017|isbn=978-3-319-55839-4|doi=10.1007/978-3-319-55840-0}}</ref>

A fault in the appliance which causes a live conductor to contact the casing will cause a current to flow in the earth conductor. If large enough, this current will trip an over-current device ([[Fuse (electrical)|fuse]] or [[circuit breaker]] [CB]) and disconnect the supply. The disconnection time has to be fast enough not to allow [[fibrillation]] to start if a person is in contact with the casing at the time. This time and the current rating in turn sets a maximum earth resistance permissible. To provide supplementary protection against high-impedance faults it is common to recommend a [[residual-current device]] (RCD) also known as a residual current circuit breaker (RCCB), ground fault circuit interrupter (GFCI), or residual current operated circuit-breaker with integral over-current protection (RCBO), which will cut off the supply of electricity to the appliance if the currents in the two poles of the supply are not equal and opposite.