World Plugs

Plugs & Sockets


Brief history

International standardization of electrical plugs and sockets for domestic use


why so many plugs

Harvey Hubbell's "Separable Attachment Plug"
(patented in 1904) - allowed for non-bulb devices
to be plugged into a light socket for power - was
designed with a simple intention:
"My invention has for its object away with
the possibility of arcing or sparking in making
connection, so that electrical power in buildings
may be utilized by persons having no electrical
knowledge or skill."

Plugs: not immediately in focus

The IEC was founded in 1906 to provide a platform to scientists so that they could build on each other's research and stimulate the development and commercialization of electrical technology and machinery.


In 1904 at the World's Fair in St. Louis scientists and engineers from around the world realized for the first time that standards for electrotechnology were urgently needed.


The exhibits that occupied the Palace of Electricity not only required electricity of numerous different voltages, but also either direct current or 1-, 2-, or 3-phase alternating current, with many different frequencies and variations of connectors and plugs.


Electricity was the new thing and it generated an increased transnational flow of ideas and products.


Scientists realized that they needed common metrics, terminology and symbols to build on each other's research, and to facilitate the development and roll-out of innovations.


During the first years of its existence, the engineers and industry representatives who worked on the IEC platform focused on standards for electrical machinery, including the associated nomenclature and symbols. It was only after the First World War (1914-1918) that their attention turned to the newer applications of electricity in the home and office.


First attempts to standardize plugs and sockets

In the early 1930s the international members of the IEC were made aware of standardization in Europe by the IFK (Internationale Fragens-Kommission - International Questions Commission) based in Holland. The organization comprised delegates from electricity suppliers (generators and distributors) as well as electrical test houses in 12 countries, including some representatives of IEC NCs (National Committees). It focused mainly on the field of electrical power distribution.


The IEC at its meeting in Paris in January 1933 decided that its CA (Committee of Action) should contact the IFK to engage collaboration in matters of mutual interest. In 1934 an IEC/IFK co-operation agreement was signed. As a result the new TC (Technical Committee) 23 was created to deal specifically with the standardization needs of electrical fittings.


The work of TC 23 took a long time to commence. The IEC CA, at its meeting in Torquay, UK in June 1938 and again in Paris, France in June 1939 urged the experts participating in TC 23 to finally schedule their first meeting and to give priority to the question of plugs and sockets. Then World War II broke out and for several years plugs and sockets were far from people's concern.


Starting standardization work

After the war, and its subsequent economic recession, work on domestic plugs and sockets got under way at the first meeting of TC 23 in Luzern, Switzerland in October 1947. By this time, the European work had moved to the CEE (International Commission on Rules for the Approval of Electrical Equipment) and TC 23 discussed a possible co-operation with the CEE in the field of 'Unification of the International Standards relating to sockets, plugs and connectors'.


The CEE work led to the first edition of its publication 7, in 1951. In essence this was simply a selection of the most widely used plugs and sockets in Europe, excluding the UK and Ireland.


At this point the IEC as a whole, and in particular all the experts participating in TC 23, realized that there was very little chance to still achieve agreement on a common standard on plugs. Over the years so many different plug types had been introduced that even in a limited regional area like Europe standardization was highly unlikely.


Nevertheless, in 1957, TC 23 issued the first edition of IEC Publication 83, Standard for plugs and socket-outlets for domestic and similar general use. This publication was essentially a collection of all the European plug and socket designs of CEE 7, as well as those of the USA and Great Britain. Many of the latter were used in a number of countries around the globe.


Rather than an International Standard, this publication was a catalogue of national standards, and this was recognized by giving its second edition in 1975 the status of a Technical Report.


The universal plug and socket system

why so many plugs

IEC-906-1 plug (now IEC60906-1)

In the early 70s, TC 64, Electrical installations, was formed and it was inevitable that, in its considerations of domestic wiring installations, it would face the problem of the plethora of plugs and sockets in use. This provided the IEC with further impetus to find a global solution or, at least, attempt to reduce the number of varieties. With this perspective in mind, the IEC created SC (Subcommittee) 23C, Worldwide plug and socket outlet system, in 1970.


The first drafts of a universal system considered by SC 23C proposed all flat pins and this was pursued for many years. However, at the voting stage, objections grew and, many NCs expressed themselves more in favour of a round pin solution. The other serious problem encountered was in trying to find a unique solution for 125V and 250V distribution systems. After long, and often acrimonious discussions, the SC came to an acceptable solution, which was finally published in 1986 as International Standard IEC 906-1 (now IEC 60906-1) for 250V installations using round pins and in 1992 as IEC 906-2 (now IEC 60906-2) for 125V installations using the familiar US flat pin design.


More recently, in the 1990s, CENELEC, in Europe, was put under pressure by the European Commission to devise a harmonized plug and socket system for Europe. Incredible as it may seem, the economic consequences of the implementation of such a universal system were never assessed (not in Europe, nor elsewhere). The view of the Commission appears to have been based entirely on political considerations!


CENELEC took as its starting point the IEC standard of 1986 and spent thousands of man-hours undertaking the almost impossible task of modifying the design with the aim of ensuring 100% risk-free operation of the system when used in conjunction with all the existing plug types in Europe. Naturally, apart from the technical difficulties, there was the clash of the many vested commercial and political interests and it was not surprising that, after much work and many meetings, CENELEC had to admit defeat and abandon its efforts, much to the chagrin of the Commission.


However, as the IEC continues to point out, internationally agreed standards for domestic plugs and sockets for the 250V and 125V ranges DO exist and are, even today, available to any country that cares to implement them. However, so far only Brazil and South Africa have adopted them.