Plugs and sockets for electrical appliances in the United Kingdom originated in the 1870s and were initially two-pin designs. These were initially sold as a mating pair, but gradually standards arose to enable the interchange of compatible devices.
In the United Kingdom, British Standards lists three types of socket-outlet systems primarily for domestic use:
The fuse-in-plug universal polarised maximum 13 A BS 1363. This family of accessories has one universal plug having a user replaceable fuse to suit the needed amperage of the appliance flex and appliance; The unfused polarised BS 546. This family of socket-outlets has four plug types of differing sizes: 2 amps, 5 amps, 15 amps, and 30 amps; The BS 4573 two-pin unpolarised socket and plug. This is a niche application socket-outlet used primarily for shavers and rechargeable toothbrushes.
A distinctive characteristic of the one BS 1363 socket-outlet and the BS 546 socket-outlet family are protective safety shutters behind the socket holes, and optional socket switches.
The BS 1363 universal socket-outlet plug differs from the BS 546 family by incorporating square pins rather than round pins and a user replaceable fuse from 1 A to 13 A.
The BS 1363, universal 13A socket-outlet system and connection units is the dominant type of single-phase socket-outlet system used in the United Kingdom, having only one plug type. The BS 546 socket-outlet family of four types tends to be used for niche applications, although the 5 A version has had a resurgence in switched lighting circuits. The BS 546 30 A plug has near disappeared from the UK market due to poor demand.
Terminology
A plug is the movable part of a socket-outlet connector attached to an electrical device. The socket connects to the power source, either fixed on a building structure or installed on an item of electrical equipment. The plug has protruding pins (male) that fit into matching contact holes (female) in the sockets. Plug-in devices with incorporated plug pins perform other functions than connecting an appliance to a supply circuit and so are not interchangeable with plugs.
Sockets and plugs are designed to prevent exposure of bare energised contacts, to reduce the risk of users accidentally touching energized conductors. Safety features may include plug pins with insulated sleeves and sockets with blocking shutters.
The term plug is in general and technical use in all forms of English, common alternatives being power plug, electric plug, and plug top.Geoffrey Boothroyd (2005), Assembly Automation and Product Design, Second Edition, CRC Press, p. 315 (retrieved 20 December 2013 from Google Books)Patrick Fullick (2001), Physics for AQA, Heinemann, p. 16 (retrieved 1 March 2013 from Google Books)Trevor Linsley (2008), Advanced Electrical Installation Work, Routledge, p. 37 (retrieved 2 March 2013 from Google Books) 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.IEC/TR 60083, Ed. 6.0, IEC, 2009 (retrieved 1 March 2013 from Techstreet) The general term is socket, but there are numerous common alternatives, including power point, plug socket, wall socket, and wall plug.Building Surveys and Reports, James Douglas, John Wiley & Sons, 2010, p. 254 (retrieved 1 March 2013 from Google Books)Wendell Odom (2004), Computer Networking First-Step, Cisco Press, p. 38 (retrieved 1 March 2013 from Google Books)Benjamin Stein (1997), Building Technology: Mechanical and Electrical Systems, John Wiley & Sons, p. 723 (retrieved 1 March 2013 from Google Books) 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.Brian Scaddan (2011), 17th Edition IEE Wiring Regulations: Explained and Illustrated, Routledge, p. 18 (retrieved 6 March 2013 from Google Books) Neutral is usually at or near earth potential, being earthed either at the substation or at the service entrance (neutral-to-earth bonding is not permitted in the distribution board/consumer unit). Line carries the full supply voltage relative to the neutral. The protective earthDave Holland, Jimmy Tzimenakis (1999), Electrical Product Safety, Newnes, p. 58 (retrieved 3 March 2013 from Google Books) 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 (in the context of plugs and sockets) 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". (There is an alternative spelling, 'adapter', but adaptor is the form usually used in standards and official documents.)
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 other types. With the exception of BS 4573 which are round 2-pin reversible plugs and shaver socket-outlets commonly used for electric shavers and toothbrushes, British Standards for plugs specify a bottom entry flex (entry in other types is usually parallel to the axes of the pins). 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. For both BS 546 and BS 1363 sockets, the left-hand contact is neutral and the right-hand contact is line.
British plugs and sockets regulatory system A Statutory Instrument, the Plugs and Sockets etc. (Safety) Regulations 1987, was introduced to specifically regulate plugs and sockets in the United Kingdom. This was revised by the Plugs and Sockets etc. (Safety) 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 (normally BSI, ASTA-Intertek or NEMKO). 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 (BS 4573) but may also be a Europlug (BS EN 50075). 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 (insulated shutter opening device) 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 (AMD 14539) 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 (British) General Electric Company catalogue of 1889. Gustav Binswanger, a German Jewish immigrant, Second Chance: Two Centuries of German-speaking Jews in the United Kingdom, edited by Werner Eugen Mosse, Julius Carlebach, Mohr Siebeck, 1991, p.362 (retrieved 20 December 2013 from Google Books) who founded the General Electric Company,, A Company of Many Parts, A. Heerding and Derek. S Jordan, Cambridge University Press, 1989, p.51 (retrieved 20 December 2013 from Google Books) obtained a patent (GB189516898) in 1895 for a plug and socket using a concentric (co-axial) 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, Electric cooking, heating, cleaning, etc: being a manual of electricity in the service of the home, Maud Lucas Lancaster, Constable & Company, Ltd., 1914, p.312 (retrieved 13 March 2013 from Google Books) Maud Lucas Lancaster mentions an earthed iron-clad plug and socket by the English firm of A. Reyrolle & Company. The 1911 General Electric Company (GEC) 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.John Mellanby (1957), History of Electric Wiring, Ch 10, London: Macdonald. 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 (capacity unspecified), and also a type of two-pole concentric plug and socket (similar to a large version of the concentric connectors used for laptop PC power connections) 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.