Schuko

[2] Büttner's company, Bayerische Elektrozubehör AG, was granted patent DE 489 003 in 1930 for a Stecker mit Erdungseinrichtung ('plug with earthing device').

At this time Germany used a 220 V centre tap giving 127 V from current pins to earth,[citation needed] which meant that fuse links were required in both sides of the appliance and double pole switches.

CEE 7/6 plugs that need to be polarised are configured in such a way as to only be inserted correctly in earthed sockets, however the old CEE 7/1 2-pin unearthed socket is inherently dangerous with equipment that should be polarised, for example table lamps with an Edison screw lamp but only a single pole inline cord switch in lieu of a double pole switch.

Russia, while maintaining its own mains connector standard, has it largely harmonised with the relevant European regulations since Soviet times.

Nowadays most sold and installed sockets in Russia are Schuko ones, though they may lack a connection to earth, especially in older buildings, as this wasn't required by the Soviet wiring regulations.

A pair of non-conductive guiding notches (4) on the left and right side provides extra stability, enabling the safe use of large and heavy plugs (e.g. with built-in transformers or timers).

Many such sockets also lack the cavity required to prevent users from touching the pins whilst inserting the plug.

In Italy, Chile, Peru and Uruguay, hybrid versions of Schuko sockets (called P 30) are seen with an extra hole that will take the smaller variant of Italian CEI 23-50 plugs.

There are also hybrid Schuko sockets (called P 40) with three extra holes and a wider cavity that will also accept the larger variant of Italian plugs.

The IEC 60906-1 standard was intended to address some of the issues regarding polarisation and replace Schuko, but the only countries that have adopted it are South Africa and Brazil.