Historical Background

A service of PlugSafe

The first mains plugs and sockets were two-pin devices developed in Britain in the early 1880s, and by the end of that decade British plugs had taken on a form which is familiar today, sturdy devices with two round pins made of solid brass.  By 1911 we know that plugs with a third earthing pin were in use in Britain, these were similar to those subsequently standardized in BS 546. 

Meanwhile, in the USA, mains plugs came much later, usually attributed to Harvey Hubbell in 1904.  These early American designs used thin flat blades which could be stamped out cheaply by the new mass production methods then making a first appearance.  The initial US design of two blades in tandem was soon replaced by the parallel blades in use there today.  A variation of those early American types with blades placed at an acute angle was patented in 1915, and in 1930 that became the basis of the plug used in Australia (and also a number of other countries including China), although its use died out in in America prior to NEMA standards. 

What became the predominant plug in mainland Europe, also having two solid round pins, was established by the 1920s when Albert BŁttner added side earthing contacts which would connect with sprung clips located in a socket recess.  At that time continental supplies were typically across two phases with no neutral connection, so the fact that there was no polarization in this ‘Schuko’ connector was not important, but the subsequent move to line and neutral supplies left the Schuko with a fundamental disadvantage that exists to this day, there is no way to distinguish between line and neutral.  The French avoided this problem by adopting an earthing pin in the socket itself.  There were various other designs used in Europe, including the Italian, Swiss and Danish types still used today.  A century ago the idea of portable electric appliances being routinely carried between countries simply did not exist, so the proliferation of different plug types throughout the world was of no particular significance, but things look very different today.

As described in the article The remarkable evolution of BS 1363 (IET Wiring Matters, Winter 2013), Britain introduced a completely new type of plug in 1947.  Malcolm Mullins has described the process that led to that change in The origin of the BS 1363 plug and socket outlet system (IET Wiring Matters, Spring 2006), but essentially a new and thoroughly modern system was designed taking into account safety, the desire for a single UK plug type, and the projected needs of a post-war society with an increasing variety of electrical appliances.  It is interesting to reflect that Britain was the only major industrialized country to make such a move, and others are still using plug designs barely adapted from those developed in the early 20th century.

Naturally, with the increase in international trade and foreign travel, consideration was given to the possibility of achieving some international standardisation.  The first IEC discussions on this took place shortly before WWII, so came to a premature halt.  They resumed in 1947 (a few months after the introduction of BS 1363), but made no actual progress.  It was not until 1970 that an IEC committee called “Worldwide plug and socket outlet system” was created.  This committee recognized the importance of distinguishing between 115V and 230V systems as a fundamental safety issue.  In 1986, after years of disagreement, the committee produced IEC 906-1 (now IEC 60906-1) for use on 200V to 250V systems.  This has the live pin spacing common to most European systems, but with a third pin for earthing set in a position which made it non-interchangeable with any other earthed plug.  It subsequently adopted the existing American plug and socket as IEC 906-2 (now IEC 60906-2) for use on 100V to 130V systems. 

Later, in the 1990s, the European Commission urged CENELEC to devise a harmonized European system which would accept all of the existing plug types; it appears that this was done with no consideration of the economic consequences!   CENELEC took IEC 60906-1 as its starting point, but unsurprisingly found that to produce a safe solution was not possible, the project was abandoned. 

IEC 60906-1 has so far been adopted only by South Africa which is in the early stages of a transition to its use.  In Brazil a new national standard was based on IEC 60906-1, but does not conform to it.  There are two versions, both of which have ratings and pin sizes differing from the original.  Brazil also commits the inexplicable folly of using both versions for 115V and 230V systems, only a label distinguishes between the two!

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