BS 1363 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 line and neutral socket holes, and a fuse in the plug. It has been adopted in many former British overseas territories; Ireland, Malaysia and Singapore have equivalent national standards. 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 replaced the former BS 546 plug, which is still found in old installations or in special applications.
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In 1941 Lord Reith, then the minister of Works and Planning, established committees to investigate problems likely to affect the post-war rebuilding of Britain. One of these, the Electrical Installations Committee, was charged with the study of all aspects of electrical installations in buildings. Convened in 1942, they reported in 1944.[1]
One of the most far reaching recommendations was the introduction of the ring circuit system (often informally called "ring main"). In this, a cable was brought from the fuse or circuit breaker in the distribution board and wired in sequence to a number of sockets in a ring, closed at the distribution board. In the ring circuit, each socket was fed current by wires on both sides of the loop. This contrasts with a system wherein a single cable runs out radially from the distribution board to serve a number of sockets, and a single wire segment must carry all of the current. The ring circuit allowed smaller wires to be used, and saved copper, which was costly immediately after the war. Since the fuse or circuit breaker had to be rated for the maximum current the ring could carry (30 A or 32 A for breaker), each plug connecting to the ring contained its own fuse, rated to protect the appliance flexible power cable.
The plug and socket system defined in BS 1363 is a result of another of the report's recommendations. Britain had previously used a combination of 5 amp and 15 amp round pin sockets, where each socket was wired to an individual fuse at the distribution board. In an appendix to the main report (July 1944), the committee proposed that a completely new socket outlet and fused plug should be adopted as the "all-purpose" domestic standard. One of the principal objectives of the new standard was stated as “To ensure the safety of young children it is of considerable importance that the contacts of the socket-outlet should be protected by shutters or other like means, or by the inherent design of the socket outlet.”[2] This requirement for a new system of plugs and sockets led to the publishing in 1947 of "British Standard 1363 : 1947 Fused-Plugs and Shuttered Socket-Outlets".[3]
Most appliances are connected with BS 1363 plugs. Exceptions include equipment requiring more than 13 amps, remotely switched lighting, and low-power portable equipment, such as shavers, which may be used in several countries. Many bathrooms, particularly in hotels, have 2-pin standard "shaver sockets", which usually accommodate both European and US 2-pin plugs.
Consumer Protection legislation in both the UK[4] and Ireland[5] requires that most domestic electrical goods sold in either country to be fitted with a BS 1363 or IS 401 (as applicable) plug.
The BS 1363 design is used in the United Kingdom and Ireland, Sri Lanka, Kuwait, Bahrain, UAE, Qatar, Yemen, Oman, Cyprus, Malta, Gibraltar, Botswana, Ghana, Hong Kong, Jordan, Macau, Brunei, Malaysia, Singapore, Kenya, Uganda, Nigeria, Iraq, Tanzania, Zambia and Zimbabwe. BS 1363 is also standard in several of the former British Caribbean colonies such as Belize, Dominica, St. Lucia, St. Vincent, and Grenada. It is also used in Saudi Arabia in 230 V installations.
The National Standards Authority of Ireland (NSAI) issued the Irish Standard "I.S. 401 Safety Requirements for Rewireable 13A Fused Plugs for Normal and Rough Use Having Insulating Sleeves on Line and Neutral Pins", which is largely similar to BS 1363. Any relevant plugs originating or sold in the country must pass the Irish Standard or an equivalent standard of a member of the European Union, which includes BS 1363.
The UK, and some other countries, also use the earlier BS 546 round-pin socket standard. BS 546 is limited to old installations or specialised applications where mating with the standard variety is not desired. For example, if a receptacle is connected to a dimmer or a switch of low current capability, use of a BS 546 receptacle and plug is intended to prevent devices other than lighting from being connected. BS 546 is also used in applications where a non-fused plug is wanted.[6]
A BS 1363 plug has two horizontal, rectangular pins for line (commonly termed "live" in the United States, but "line" is the term used in BS 1363, per British practice) and neutral, and above these pins, a larger, vertical pin for an earth connection. Unlike most other types of sockets, the earth pin is necessary for use of the BS 1363 plug, as it is needed to push open a shutter in the socket to allow the line and neutral pins to be inserted. It also polarises the plug, ensuring that the line pin is connected to the correct terminal in the socket. Moulded plugs for unearthed, double-insulated appliances may instead have a non-conductive plastic pin (an Insulated Shutter Opening Device or ISOD), to open the shutters.
BS 1363 part 1 is the specification for the plug. As there are no moving parts in a plug it is practicable to define the dimensions of the plug in an absolute manner. BS 1363 part 2 contains the specifications for sockets, to allow some flexibility in design the socket is defined partly in terms of the plug with which it will be used.
BS 1363 sockets have shutters on the line and neutral contacts to prevent the insertion of a foreign object into the socket. Most sockets use the original method of shutters opened by the earth pin ( or plastic ISOD) alone. Alternatively, shutters may be opened by simultaneous insertion of line and neutral pins. Some recent designs require all three pins to be inserted simultaneously.
Automatic shutters for protection dates back to at least 1927.[7] Other countries, for example the USA [8], are gradually requiring their sockets to be protected by shutters also. Many extension sockets allow a plug to be inserted upside down, defeating the shutter mechanism. This method is sometimes used to allow a European-style plug (with two small round pins and no earth pin) to be inserted into the open line and neutral ports. Socket covers are sold, putatively to protect children from insertion of metal objects into socket pins. The shutters of the BS 1363 make these unnecessary, and improperly inserted covers can defeat the shutter mechanism. [9]
Initially, BS 1363 did not require the line and neutral pins to have insulating sleeves. Plugs made to the recent revisions of the standard have insulated sleeves to prevent finger contact with pins, and also to stop metal objects (for example, fallen window blind slats) from becoming live if lodged between the wall and a partly pulled out plug. The length of the sleeves prevents any live contacts from being exposed while the plug is being inserted or removed.
The line and neutral pins have a rectangular cross section 6.35±0.13 mm wide and 3.975±0.075 mm height. They are 17.7±0.5 mm long and their centre lines are horizontally 11.115±0.065 mm on either side of the symmetry plane of the plug. The protective-earth pin is 22.73±0.5 mm long and is 3.975±0.075 mm wide and 7.925±0.125 mm high. The centre lines of the line/neutral pins and the protective pin are vertically 22.23±0.13 mm apart. The millimetre dimensions were soft-converted from the original inch dimensions which no longer appear in the standard.
Dimensions are chosen to provide safe clearance to live parts. The distance from any part of the line and neutral pins to the periphery of the plug base must be not less than 9.5 mm. This ensures that nothing can be inserted alongside a pin when the plug is in use, and helps keep fingers away from the pins (this was a very early modification to the standard). The minimum insertion distance from the face of the socket to the first point of contact with a live part is 9.6 mm.
The longer earth pin ensures that the earth path is connected before the live pins, and remains connected after the live pins are removed. The earth pin is too large to be inserted into the phase or neutral sockets by mistake.
The plug is polarised, so that the fuse is in the line side of the supply. The standard specifies retention force for the contacts, so that the plug is difficult to dislodge by accidental knocks or strains on the flexible cord. The flexible cord always enters the plug from the bottom, discouraging removal by tugging on the cable, which can damage the cable. The internal arrangement of the terminals ensures that if the cable is pulled out of the plug, the line wire breaks first.
As with many other commodities, counterfeit plugs and fuses not meeting the standard are occasionally found. Legislation [10] was introduced, with last revision in 1994, to require plugs sold to meet the technical standard. Counterfeit products are regularly seized when found, to enforce the safety standards and to protect the trademarks of imitated manufacturers. [11]
Because typical British ring circuits can deliver more current than appliance flexible power cords can handle, BS 1363 plugs are required to carry a cartridge fuse. [12]) The fuse is manufactured to BS 1362. The maximum load that can be placed on a socket is 13 A; triple and larger sockets are fitted with a 13 A fuse of the same type used in the plugs. The former BS546 standard relied on different sized sockets, and fuses installed at the consumer unit to protect both the permanent wiring and the appliance flexible cord.
Fuses are available in different ratings and are colour coded: 2 (black or blue), 3 (red), 5 (black or grey), 10 (black or yellow), and 13 (brown) amps. BS 1362 requires fuses with any other current rating to be marked in black. The most common ratings are 3 and 13 amps. Plugs when supplied separately from any appliance come with a 13 A fuse. The fuses are mechanically interchangeable; it is up to the end user or appliance manufacturer to install the appropriate rating.
BS 1362 specifies sand-filled ceramic-bodied cylindrical fuses, 1" (25.4 mm) in length, with two metallic end caps of 1/4" (6.3 mm) diameter and roughly 1/5" long. The standards specifies breaking time versus current characteristics only for 3 A or 13 A fuses.
Plugs for hand-wiring are commonly available and are usually attached with instruction cards displaying recommended wire lengths. They can be assembled or opened with a screwdriver. Most modern products come fitted with moulded plugs with removable fuse sections.
The secondary school physics syllabuses in the United Kingdom, Hong Kong and Singapore include the procedure for wiring BS 1363 plugs, as well as the concept of a ring circuit and a radial circuit (except in Hong Kong). In Malaysia, however, the procedure for wiring BS 1363 plug are taught in Living Skills subject (Kemahiran Hidup) for Form 1 (secondary school year 1) students.
In Ireland, secondary school students learn the procedure for wiring BS 1363 plugs as well as other wiring concepts.
Due to the size of the BS 1363 plug, attempts have been made to develop a compatible folding plug. As of May 2011 two of these have been approved for sale, the SlimPlug and the ThinPlug. SlimPlug is available only as part of a complete power lead terminating in an IEC 60320 C7 unpolarized connector.[13] In 2009 the ThinPlug received a "Red Dot" award [14] for product design, the first products incorporating it[15] are due to go on sale in June 2011. Another design concept, the Folding Plug, [16] featuring a pivot which allows the plug's pins to be aligned vertically, won the Brit Insurance design of the year award in 2010,[17] but as described in the promotional video it does not meet BS 1363, and has not been approved for sale in the UK.
Several manufacturers have made deliberately incompatible variants for use where connection with standard plugs and sockets is not acceptable. Examples include filtered supplies for computer equipment and cleaners' supplies in public buildings and areas (to prevent visitors plugging things in). The most commonly seen variant is one made by MK that has a T-shaped earth pin.
Sockets for Walsall Gauge 13 A plugs can be seen in some London Underground stations.
Plug adapters permit two or more plugs to share one socket. There are several common types, including double- and triple-socket blocks, shaver adapters, and multi-socket strips.
BS 1363 allows doublers to be unfused and in practice fused doublers are very rare. Current standards require triplers on the other hand to be fused so there is a fuse there to protect them if overloaded. Older triplers do not have a fuse. In the photo the adapter on the left is a tripler and the red fuse carrier can easily be seen.
The main purpose of these adapter is to accept the 2 pin plugs of UK shavers, as marked on such adapters. These adapters usually have a 1 A or 2 A BS 646 or BS 1362 fuse. As well as the British Shaver plugs they are generally designed to accept Europlugs and American 2 pin plugs and sometimes Australian 2 pin plugs. In many cases Schuko and French plugs will also fit but there is no earth contact with such plugs. The current rating of the adapter should also be considered before connecting equipment other than shavers.
A conversion plug is a special type of plug suitable for the connection of non-BS 1363 type plugs (to a recognized standard) to BS 1363 sockets outlets. An example would be Class 2 appliances from mainland Europe which are fitted with moulded europlugs. Unlike a temporary travel adapter, these plugs, when closed resemble normal plugs, although larger and squarer. The europlug is inserted into two metal clip contacts, and the hinged body of the conversion plug is closed and screwed shut to grip the europlug. A tool must be used to remove the conversion plug. These plugs have a plastic earth pin and an accessible fuse. In some cases the plugs are fitted with screws that are made to be difficult to unscrew. Similar converters are available for a variety of other plug types but do not seem to be seen much in practice.
For example, conversion plugs are supplied for British sales of recent Class 2 Sony electrical products with permanently fixed flexible cords, instead of moulded BS1363 plugs.
BS 1363 is periodically revised, with major revisions issued in 1967 and 1984, and supplements issued between major revisions. BS 1363:1984 and earlier versions dealt with only 13 A plugs and sockets. In 1995 the standard was revised and divided into four parts as follows:
In 2008 a fifth part was added:
Switched and unswitched fused connection units, without sockets, use BS 1362 fuses for connection of permanently wired appliances to a socket circuit. They are also used in other situations where a fuse or switch (or both) is required, such as when feeding lighting off a socket circuit, to protect spurs off a ring circuit with more than one socket, and sometimes to switch feeds to otherwise concealed sockets for kitchen appliances.