"Schuko" is the colloquial name for a system of AC power plugs and sockets that is defined
as "CEE 7/4". A Schuko plug features two round pins of 4.8 mm diameter for the line and
neutral contacts, plus two flat contact areas on the top and bottom side of the plug for
protective earth. Schuko sockets form a cavity into which the plug is inserted. Schuko plugs
and sockets are symmetric AC connectors. They can be mated in two ways, therefore line and
neutral can arrive on either pin at the consuming device. 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, which indicates that plug and socket are equipped with protective-earth
contacts. 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 patent
DE 370538 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 earth connection. 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 a type of plug and 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-on Schuko plugs, and good-quality
rewirable replacements, are a hybrid version with an extra hole that also accommodates
the earth pin of French sockets. French plugs that need to be polarised are configured in
such a way as to only be inserted correctly in grounded sockets, however the old 2-pin
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 standard across Europe and in many other countries
that follow CENELEC standards. European countries that do not use CEE 7/7 are:
Denmark. Ireland but see below,
Italy, Malta,
Cyprus, The United Kingdom, including Gibraltar
Switzerland 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. A minority of 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 in Belgium or France, it is sometimes encountered
in older installations in eastern regions of Belgium and Alsace. Newer installations
should be adhering to CENELEC and older state standards are obsolete.
In parts of the Republic of Ireland, Schuko was commonly installed until the 1960s. For
safety reasons and to harmonize with the UK and avoid having a different outlet type in
Northern Ireland and the Republic of Ireland, the Republic standardized on BS 1363 and IS411.
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 since Schuko
introduction was modified to include its specifications, due to the large volume of imported appliances
equipped with the Schuko plug. This was necessitated by the fact that 4 mm holes in the Soviet
sockets could not accept 4.8 mm Schuko pins without modification. Nowadays most sold and
installed sockets in Russia are Schuko ones, though they may lack grounding wire connection,
especially in older buildings, as this wasn't required by the Soviet wiring regulations.
Safety features
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. Compatibility with other plug/socket types
Schuko sockets can accept two-pin unearthed Europlug and CEE 7/17. Less safely, Schuko
plugs can be inserted into many two-pin unearthed sockets and into some sockets with a different
form of earth connection that will not mate with the earth contacts on the Schuko plug.
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.
See also Europlug
AC power plugs and sockets GOST 7396 Soviet Version
IEC 60906-1 Proposed replacement References
^ "ABL SURSUM, Company". DE: ABL SURSUM. ^ "DE370538". DE: European Patent Office.
German standard DIN VDE 0620-1; VDE 0620-1:2010-02 Plugs and socket-outlets for household and
similar purposes - Part 1: General requirements German standard DIN 49440-1:2006: Two-pole
socket-outlets with earthing contact, 16 A 250 V AC - Part 1: Main dimensions
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 IEC/TR 60083
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