Position of ground contact sleeve with respect to major keyway for various voltages and frequencies. The colour codes correspond to the nominal voltage.
* Clock positions not normed and free for use for special applications.
**Clock positions not used.
Plugs and sockets with rated voltages above 50V must have an earth contact. To prevent incorrect insertion, a nose on the plug fits into a keyway in the receptacle, thus ensuring that the earth contact pin or tube is correctly positioned in accordance with the required electrical standard. The earth contact positions for the various frequencies and voltages are assigned a clockface position, in accordance with table 104 taken from EN 60309-2:1999 + A1:2007 + A2:2012.
Unintentional incorrect mating is prevented by the fact that the contact pin for the protective conductor has a larger diameter than the outer conductor contact pins and thus can not be inserted into the outer conductor contact sockets. It must not be possible for the user to change the position of the protective contact or any existing N-contact to the groove of a socket or nose of a plug. It must also be prevented to be able to use a plug insert in a socket or coupling housing.
On rewirable plugs and sockets the contacts must be marked with symbols as follows:
The contact tubes of receptacles and connectors with rated voltages above 50V must be arranged clockwise as viewed from the front.