Editing AC power plugs and sockets (section)

=== Earthing (grounding) ===
A third contact for a connection to [[Ground (electricity)|earth]] is intended to protect against insulation failure of the connected device. Some early unearthed plug and socket types were revised to include an earthing pin or phased out in favour of earthed types. The plug is often designed so that the earth ground contact connects before the energized circuit contacts. The assigned IEC [[appliance classes|appliance class]] is governed by the requirement for earthing or equivalent protection. Class&nbsp;I equipment requires an earth contact in the plug and socket, while Class&nbsp;II equipment is unearthed and protects the user with [[Appliance classes#Class II|double insulation]].

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