Schuko

"Schuko" () is a registered trademark referring to a system of AC power plugs and sockets that is defined as " CEE 7/3" (sockets) and "CEE 7/4" (plugs). A Schuko plug features two round pins of 4.8 mm diameter (19 mm long, centers 19 mm apart) for the line and neutral contacts, plus two flat contact areas on the top and bottom side of the plug for protective earth ( ground). The socket (which is often, in error, also referred to as CEE 7/4) has a predominantly circular recess which is 17.5 mm deep with two symmetrical round apertures and two earthing clips on the sides of the socket positioned to ensure that the earth is always engaged before live pin contact is made. Schuko plugs and sockets are symmetric AC connectors. They can be mated in two ways, therefore line can be connected to either pin of the appliance plug. As with most types of European sockets, Schuko sockets can accept Europlug of the German term ' (literally: protective contact), which indicates that plug and socket are equipped with protective-earth contacts (in the form of clips rather than pins). Schuko connectors are normally used on circuits with 230  V, 50  Hz, for currents up to 16  A.

History

The Schuko system originated in Germany. It is believed to date from 1925 and is attributed to Albert Büttner, a Bavarian manufacturer of electrical accessories. Büttner's company, , was granted patent DE 489 003 in 1930 for a ('plug with earthing device'). Büttner's patent DE 370 538 is often quoted as referring to Schuko, but it actually refers to a method of holding together all of the parts of a plug or socket with a single screw which also provides clamping for the wires; there is no mention of an earth connection in DE 370538. At this time Germany used a 220 V centre tap giving 127 V from current pins to earth, which meant that fuse links were required in both sides of the appliance and double pole switches. Variations of the original Schuko plug are used today in more than 40 countries, including most of Continental Europe.

France, Belgium, the Czech Republic, Slovakia and Poland use the CEE 7/6 plug and CEE 7/5 socket with the same size and spacing of the main pins but with a male protective-earth pin on the socket instead of the earth clips, and without the guiding notches at the sides. Most modern moulded Schuko plugs, and good-quality rewirable replacements, are a hybrid version ("CEE 7/7") with an aperture that accommodates the earth pin of CEE 7/5 sockets. 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. The safety of polarisation was not helped by several years of confusion when the correct connection of sockets was transposed.

CEE 7/7 has now become the ''de facto'' plug standard in many European countries, and in some other countries that follow CENELEC standards. European countries that do not use CEE 7/7 are:
*Denmark (CEE 7/17 and Danish standard 107-2-D1 are widely used, they accept CEE 7/7 plugs but without compatibility for earth connections. CEE 7/5 and CEE 7/3 sockets with child-proof shutters have been allowed since 2008/2011, but people are not using them yet).
*Ireland (BS 1363 / Equivalent Irish Standard: IS 401) but see below,
*Italy (CEI 23-50),
*Malta (BS 1363),
*Cyprus (BS 1363),
*The United Kingdom, including Gibraltar (BS 1363)
*Switzerland (SN 441011)

In Italy, CEI 23-50 is the dominant standard and it includes also Schuko sockets (P 30 = CEE 7/3) and plugs (S 30 = CEE 7/4, S 31 = CEE 7/7, S 32 = CEE 7/17). Appliances are commonly sold with Schuko-type plugs (as well as Europlug, with its cultural, economic and tourist connections with Austria.

Although Schuko has never been a standard (or the de facto norm) in Belgium or France, it is sometimes encountered in older installations in eastern regions of Belgium and Alsace.

In Ireland, Schuko was commonly installed until the 1960s. For safety reasons and to harmonize with the UK and thereby avoid having a different outlet type in Northern Ireland and the Republic of Ireland, the Republic standardized on BS 1363 (transposed into Irish Standards as IS 401 (Plug) and IS 411 (Socket outlet). Schuko has been phased out of use in Ireland and will be encountered very rarely. Some hotels provide a Schuko outlet alongside BS 1363 outlets for the convenience of visitors from the Continent.

Russia, while maintaining its own mains connector standard, has it largely harmonised with the relevant European regulations since Soviet times. The original Soviet standard was mostly compatible with europlug) and establishes protective-earth connection through the earth clips (2) ''before'' the line and neutral pins (3) establish contact, thereby preventing users from touching connected pins. 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).

Some countries, including Portugal, Finland, Denmark,Danish Safety Technology Authority
/ref> Norway and Sweden, require child-proof socket shutters; the German DIN 49440-1:2006-01 standard does not have this requirement.

Compatibility with other plug/socket types

Schuko sockets can accept two-pin unearthed Europlug

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