Schuko (), also designated as plug Type F, is a connector (plug/socket) system used in much (but not all) of Europe. It 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) as part of the CEE 7 standards. As with most types of European sockets, Schuko sockets can accept "Type C" Europlugs. Schuko is a syllabic abbreviation 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, although e.g. South Korea uses them at 60 Hz for historical reasons.
Description
A Schuko plug features two round pins of 4.8 mm diameter (19 mm long, centres 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. 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.
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, 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 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.
Safety features
When inserted into the socket, the Schuko plug covers the socket cavity (1), thereby preventing users from touching connected pins. It also establishes protective-earth connection through the earth clips (2) before the line and neutral pins (3) establish contact. 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, Sweden, and Italy 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.
The CEE 7/7 plug is a hybrid which includes both side earthing strips, as in CEE 7/4 Schuko, and an earthing aperture, as in the CEE 7/6 plug. It can therefore achieve an earth contact with both CEE 7/3 (Schuko) and CEE 7/5 sockets. 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. Schuko sockets are unpolarised; there is no way of differentiating between the two live contacts (line which is approximately 230 V to earth and neutral which is approximately 0 V to earth) unless the voltage to earth is measured prior to use. Although Schuko is incompatible and the pin spacing should not allow it, as the Schuko pins are slightly closer together, it is possible to dangerously force many Schuko round pin plugs (where the plastic is compliant enough) into many UK BS 1363 rectangular pin sockets, using a match or other probe to push into the earth shutter release. Due to the minimal contact area that must transmit high current, there is risk of overheating and thus fire. Where earthing is required, no earth contact will be made as Schuko plugs use side contacts for earthing rather than a third pin, and BS 1363 sockets have shutters that require the longer earth pin to be entered to open the line and neutral shutters, which prevent Europlugs and Schuko plugs from being inserted. 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.
Use within Europe
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