AC power plugs and sockets: British and related types


Plugs and sockets for electrical appliances not hardwired to mains electricity originated in the United Kingdom in the 1870s and were initially two-pin designs. These were usually sold as a mating pair, but gradually de facto and then official standards arose to enable the interchange of compatible devices.
BS 1363, 13 A plugs socket-outlets adaptors and connection units is a British Standard which specifies the most common type of single-phase AC power plugs and sockets that are used in the United Kingdom. Distinctive characteristics of the system are shutters on the neutral and socket holes, and a fuse in the plug. It has been adopted in many former British colonies and protectorates. BS 1363 was introduced in 1947 as one of the new standards for electrical wiring in the United Kingdom used for post-war reconstruction. The plug and socket replaced the BS 546 plugs and sockets, which are still found in old installations or in special applications. BS 1363 plugs have been designated as Type G in the IEC 60083 plugs and sockets standard. In the United Kingdom and in Ireland, this system is usually referred to simply as a "13 amp plug" or a "13 amp socket".
BS 546, Two-pole and earthing-pin plugs, socket-outlets and socket-outlet adaptors for AC circuits up to 250 V is an older British Standard for three-pin AC power plugs and sockets: four sizes with current capacities from 2 A to 30 A. Originally published in April 1934, it was updated by a 1950 edition which is still current, with eight amendments up to 1999. BS 546 is also the precursor of current Indian and South African plug standards. The 5 A version has been designated as Type D and the 15 A as Type M in the IEC 60083 plugs and sockets standard. BS 546 plugs and sockets are still permitted in the UK, provided the socket has shutters. In the United Kingdom and in Ireland this system is usually referred to by its pin shape, simply being known as "round pin plugs" or "round pin sockets". It is often associated with obsolete wiring installations – or where it is found in modern wiring, it is confined to special use cases, particularly switch-controlled lamps and stage lighting.

Concepts and terminology

The International Electrotechnical Commission publishes IEC 60050, the International Electrotechnical Vocabulary.
Generally the plug is the movable connector attached to an electrically operated device's mains cable, and the socket is fixed on equipment or a building structure and connected to an energised electrical circuit. The plug has protruding pins that fit into matching apertures in the sockets. A plug is defined in IEC 60050 as an "accessory having pins designed to engage with the contacts of a socket-outlet, also incorporating means for the electrical connection and mechanical retention of flexible cables or cords". A plug therefore does not contain components which modify the electrical output from the electrical input. There is an erroneous tendency to refer to power conversion devices with incorporated plug pins as plugs, but IEC 60050 refers to these as 'direct plug-in equipment' defined as "equipment in which the mains plug forms an integral part of the equipment enclosure so that the equipment is supported by the mains socket-outlet". In this article, the term 'plug' is used in the sense defined by IEC 60050. Sockets are designed to prevent exposure of bare energised contacts.
To reduce the risk of users accidentally touching energized conductors and thereby experiencing electric shock, plug and socket systems often incorporate safety features in addition to the recessed contacts of the energized socket. These include plugs with insulated sleeves, sockets with blocking shutters, and sockets designed to accept only compatible plugs inserted in the correct orientation.
The term plug is in general and technical use in all forms of English, common alternatives being power plug, electric plug, and plug top. The normal technical term for an AC power socket is socket-outlet, but in non-technical common use a number of other terms are used. The general term is socket, but there are numerous common alternatives, including power point, plug socket, wall socket, and wall plug. Modern British sockets for domestic use are normally manufactured as single or double units with an integral face plate and are designed to fit standard mounting boxes.
Electrical sockets for single phase domestic, commercial and light industrial purposes generally provide three electrical connections to the supply conductors. These are termed neutral, line and earth. Both neutral and line carry current and are defined as live parts. Neutral is usually at or very near to earth potential, being earthed either at the substation or at the service entrance. Line carries the full supply voltage relative to the neutral. The protective earth connection allows the exposed metal parts of the appliance to be connected to earth, providing protection to the user should those exposed parts inadvertently come into contact with any live parts within the appliance. Historically, two-pin sockets without earth were used in Britain, but their use is now restricted to sockets specifically designated for shavers and toothbrushes.
An adaptor is defined in IEC 60050 as "a portable accessory constructed as an integral unit incorporating both a plug portion and one or more socket-outlet portions".

Common characteristics

There are certain characteristics common to British mains plugs and sockets intended for domestic use. The brass pins appear relatively solid and large compared to others. British Standards for plugs have always specified side entry flex. Since 1934, the contacts of a socket have been specified in terms of the pins of the plug, rather than by specifying the contact dimensions. The pins of both round pin and rectangular pin plugs are arranged in a triangular fashion, the earth pin being the larger and longer pin at the apex. Earthed sockets are designed to be incompatible with two-pin plugs. Both BS 546 and BS 1363 sockets, when viewed from the front with the earth uppermost, have the line aperture at the lower right.

British plugs and sockets regulatory system

A Statutory Instrument, the Plugs and Sockets etc. Regulations 1987, was introduced to specifically regulate plugs and sockets in the United Kingdom. This was revised by the Plugs and Sockets etc. Regulations 1994. The guidance notes to the 1994 regulations state:
The regulations include a requirement that all plug types must be tested and certified by a nominated approval body. They also require that all mains appliances for domestic use in the UK be supplied with approved BS 1363 plugs, but there is an exception for plugs fitted to shavers and toothbrushes which are normally a UK shaver plug but may also be a Europlug. The regulations also contain a provision for the approval of non-BS 1363-conforming plugs when "the plugs are constructed using an alternative method of construction which provides an equivalent level of safety in respect of any risk of death or personal injury to plugs which conform to BS 1363 and is such that plugs of that type may reasonably be expected to be safe in use". Certifying bodies have used this provision by developing their own standards for novel devices, thus allowing the introduction of innovative developments; an example is the plastic ISOD which was originally approved against either an ASTA Standard or the BSI PAS 003before becoming incorporated into BS 1363-1:1995 at the second amendment in 2003.
There is no European Union regulation of domestic mains plugs and sockets; the Low Voltage Directive specifically excludes domestic plugs and sockets. As such, no relevant retained EU law applies. EU countries each have their own regulations and national standards and CE marking is neither applicable nor permitted on plugs and sockets. Despite this CE marking is sometimes fraudulently used, especially on universal sockets.

Early history

When electricity was first introduced into houses, it was primarily used for lighting. As electricity became a common method of operating labour-saving appliances, a safe means of connection to the electric system other than using a light socket was needed. According to British author John Mellanby the first plug and socket in England was introduced by T. T. Smith in 1883, and there were two-pin designs by 1885, one of which appears in the General Electric Company catalogue of 1889. Gustav Binswanger, a German Jewish immigrant who founded the General Electric Company, obtained a patent in 1895 for a plug and socket using a concentric contact system.
The earthed consumer plug has several claimants to its invention. A 1911 book dealing with the electrical products of A. P. Lundberg & Sons of London describes the Tripin earthed plug available in 2.5 A and 5 A models. The pin configuration of the Tripin appears virtually identical to modern BS 546 plugs. In her 1914 book Electric cooking, heating, cleaning, etc Maud Lucas Lancaster mentions an earthed iron-clad plug and socket by the English firm of A. Reyrolle & Company. The 1911 General Electric Company Catalogue included several earthed sockets intended for industrial use.

British two-pin plugs and sockets

The earliest domestic plug and socket is believed to be that patented by T. T. Smith in 1883. This was shortly followed by patents from W. B. Sayers and G. Hookham; these early designs had rectangular plugs with contact plates on either side. In 1885, two-pin plug designs appeared and in 1889 there were two-pin plugs and sockets in the GEC catalogue. The 1893 GEC Catalogue included three sizes of what was described as Double plug Sockets with capacities described not in amps, but as "1 to 5 lights", "5 to 10 lights" and "10 to 20 lights". These were clearly recognisable as two-pin plugs and sockets, but with no indication as to pin size or spacing, they were sold as pairs. The same catalogue included lampholder plugs for both BC and ES lampholders, and also a type of two-pole concentric plug and socket in the "1 to 5 lights" and "5 to 10 lights" capacities. Crompton and Company introduced the first two-pin socket with protective shutters in 1893, and the Edison & Swan Company was also manufacturing two-pin plug and sockets in the 1890s.
By the time the 1911 GEC Catalogue was published two-pin plugs and sockets were being offered with specifications in amps, but still with no indication as to pin size or spacing. The Midget Gauge was rated at 3 A, the Standard Gauge rated at 5 A, and the Union Gauge rated at 10 A. Also offered were two-way and three-way "T pieces" or multi-way adaptors for the 3 A and 5 A plugs, two-way only for the 10 A. Versions of the concentric plug and socket were now offered rated at 5 A and 10 A. At the same time Lundberg were offering the 2.5 A Dot, 5 A Universal, and 15 A Magnum, and Tucker were offering a range of 5 A, 10 A and 20 A plugs and sockets.
BS 73 Wall plugs and sockets was first published in 1915, and revised in 1919 with the addition of 15 A and 30 A sizes. By the 1927 revision of BS 73 four sizes of two-pin plugs and sockets were standardized: 2 A, 5 A, 15 A, and 30 A. This was later superseded by BS 372:1930 part 1 Two-pin Side-entry Wall Plugs And Sockets for Domestic Purposes. Following the introduction of BS 4573 in 1970 there were no longer any UK domestic uses for two-pin sockets except for shavers, so BS 372 was renamed "Two-pin Side-entry Wall Plugs And Sockets For Special Circuits" and subsequently withdrawn.
Current rating30 A15 A5 A2 A
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