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"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 connected to either pin of the appliance plug. As with most types of European sockets, Schuko sockets can accept Europlugs. Schuko plugs are considered a very safe design when used with Schuko sockets but they can also mate with other sockets to give an unsafe result.
"Schuko" is a short form of the German term Schutzkontakt (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.
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, Bayerische Elektrozubehör AG, was granted patent DE 489 003 in 1930 for a Stecker mit Erdungseinrichtung (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 center tap giving 110 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 clip,s 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.
- 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 23-16/VII),
- Malta (BS 1363),
- Cyprus (BS 1363),
- The United Kingdom, including Gibraltar (BS 1363)
- Switzerland (SEV 1011)
In Italy, CEI 23-16/VII is the dominant standard, though Schuko is also an approved standard and is in common use. Appliances are sold with either Italian or Schuko-type plugs. Some sockets accept both types, the remainder accepting one or the other. Schuko sockets are most commonly used for larger-rated appliances such as washing machines, and are particularly common in South Tyrol, 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. Newer installations should be adhering to current National standards.
In parts of the Republic of Ireland, Schuko was commonly installed until the 1960s. For safety reasons and to harmonize with the UK (with which Ireland has a long-standing free travel arrangement) and 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 (the traditional Soviet plug used straight 4 mm pins with 19 mm spacing and thus Soviet sockets were able to easily accept europlugs), and has been modified to accept 4.8 mm pins, due to the large volume of imported appliances equipped with the Schuko plug. 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.
When inserted into the socket, the Schuko plug covers the socket cavity (1) 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, 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 (CEE 7/16) and CEE 7/17. Less safely, Schuko plugs can be inserted into many two-pin unearthed CEE 7/1 sockets and into some sockets with a different form of earth connection that will not mate with the earth contacts on the Schuko plug (e.g., some variants of the Danish socket). Many such sockets also lack the cavity required to prevent users from touching the pins whilst inserting the plug.
In Italy, Chile and Uruguay, hybrid versions of Schuko sockets are seen with an extra hole that will take the smaller variant of Italian CEI 23-16/VII plugs. There are also hybrid Schuko sockets with three extra holes and a wider cavity that will also accept the larger variant of Italian plugs.
Schuko sockets are unpolarised; if there is a need to be sure which side is line, the socket's polarity must be tested every time.
The IEC 60906-1 standard was intended to address some of the issues in regards to polarisation and replace Schuko, but the only country to have adopted it is South Africa.
-  Schuko trademark association
- "ABL SURSUM, Company". DE: ABL SURSUM.
- "Patentschrift Nr. 489 003" (PDF). DE: German Patent and Trade Mark Office.
- "DE370538". DE: European Patent Office (EPO).
- Danish Safety Technology Authority
- German standard DIN VDE 0620-1; VDE 0620-1:2010-02 Plugs and socket-outlets for household and similar purposes - Part 1: General requirements (safety requirements)
- German standard DIN 49440-1:2006: Two-pole socket-outlets with earthing contact, 16 A 250 V AC - Part 1: Main dimensions (Schuko sockets)
- German standard DIN 49441:91972 Two-pole plugs with earthing-contact 10 A 250 V≅ and 10 A 250 V–, 16 A 250 V∼: Main dimensions (Schuko plugs)
- IEC/TR 60083
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