BS 1363

Top: a typical moulded BS 1363 plug, showing the fuse access from the underside of the plug. Bottom: a typical rewireable plug; the large central screw releases the cover, allowing access to the terminals and also the fuse

BS 1363 is a British Standard which specifies the most common type of single-phase AC power plugs and socket-outlets 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, Hong Kong, Malaysia and Singapore have equivalent 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 and socket-outlets replaced the BS 546 plug and socket-outlets, which are still found in old installations or in special applications.

Origins

BS 1363:1947 "Fused-Plugs and Shuttered Socket-Outlets" which resulted from the report "Post-War Building Studies No. 11, Electrical Installations"

BS 1363 type electrical socket-outlet. The closed shutters block entry of foreign objects

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.

The plug and socket-outlet system defined in BS 1363 is a result of one of the report's recommendations. Britain had previously used a combination of 2 amp, 5 amp and 15 amp round pin socket-outlets. 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. The main report listed 8 points to consider in deciding the design of the new standard. The first of these 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.” Others included flush fitting, no need for a switch, requirements for terminals, bottom entry for the cable, and contact design. The appendix added 5 further "points of technical detail" including requirements that plugs could not be inserted incorrectly, should be easy to withdraw, and should include a fuse.

This requirement for a new system of plugs and socket-outlets led to the publishing in 1947 of "British Standard 1363:1947 Fused-Plugs and Shuttered Socket-Outlets".

One of the other recommendations in the report was the introduction of the ring circuit system (often informally called a "ring main"). In this arrangement a cable connected to a fuse, or circuit breaker, in the distribution board was wired in sequence to a number of socket-outlets before being terminated back at the distribution board, thus forming a ring final circuit. In the ring circuit, each socket-outlet was supplied with current by conductors on both sides of the 'loop.' This contrasts with a system wherein a single cable runs out radially, like a spoke, from the distribution board to serve a number of socket-outlets. 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 requires a fuse, rated to protect the appliance flexible power cable. The ring circuit in the UK requires the use of BS 1363 plugs and socket-outlets, but the BS 1363 system is not limited to use with ring circuits.

Adoption

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 and Ireland requires that most domestic electrical goods sold in either country be fitted with a BS 1363 or IS 401 (as applicable) plug.

The BS 1363 design is used in the United Kingdom, the Republic of 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-outlet 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.

Design

A BS 1363 plug has two horizontal, rectangular pins for line (commonly termed "live" or "hot" 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 socket-outlets, 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-outlet. 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 specifies the dimensions of plug pins and their disposition with respect to each other in precise, absolute terms. BS 1363 socket-outlets are required to mate correctly with BS 1363 plugs (as opposed to the dimensions of the socket contacts being specified). This is checked by means of the use of various gauges which are specified in the standard; these gauges ensure that the socket contacts are correctly positioned and make effective and secure contact with the plug pins. There is no provision for establishing the interchangeability with any other device having plug pins incorporated, but which is not covered by BS 1363 (for example a charger or socket cover) unless that device conforms precisely to the plug pin dimensions specified.

Nominal dimensions

The line and neutral pins have a rectangular cross section 6.4 mm by 4.0 mm, 17.7 mm long and with centres 22.2 mm apart. The protective-earth pin is a rectangular cross section 8.0 mm by 4.0 mm, 22.3 mm long and with a centre line 22.2 mm from the line/neutral pin centre line. The dimensions were originally specified in decimal inches with asymmetric tolerances and redefined as minimum and maximum metric dimensions in BS 1363:1984.

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. The minimum insertion distance from the face of the socket-outlet 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 line or neutral sockets by mistake.

Ratings

BS 1363 plugs and sockets are rated for use at a maximum of 250 V ac and 13 A, with the exception of non-rewireable plugs which have a current rating according to the type of cable connected to them and the fuse fitted. The rating must be marked on the plug, and in the case of non-rewireable plugs the marking must be the value of the fuse fitted by the plug manufacturer in accordance with table 2 of the standard. Typical ratings for non-rewireable plugs are 3 A, 5 A, 10 A and 13 A.

Shutters

BS 1363 socket-outlets have shutters on the line and neutral contacts to prevent the insertion of a foreign object into the socket. Most socket-outlets 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. Other countries, for example the USA, are gradually requiring their socket-outlets to be protected by shutters also. Many extension socket-outlets will allow a plug to be inserted upside down, i.e. only the earth pin, defeating the shutter mechanism. This method is sometimes used to allow a Europlug (with two small round pins and no earth pin) to be inserted into the open line and neutral ports.

As in countries using other socket-outlet types, socket covers are sold, putatively to protect children from insertion of metal objects into sockets. According to a UK government publication, the shutters of the BS 1363 socket-outlet make these unnecessary. The UK government does not collect statistics of injury or accidents related to use of socket covers.

The Institution of Engineering and Technology has published an article on socket covers in its journal "Wiring Matters". The article by Mark Coles - the Institution's Technical Regulations Manager concludes that: "Socket-outlets to BS 1363 are the safest in the world and have been since they were first designed in the 1940s. Socket protectors are not regulated for safety, therefore, using a non-standard system to protect a long established safe system is not sensible."

A UK-based group called "FatallyFlawed" notes that none of the available socket covers are made to BS 1363 dimensions and so can introduce hazards, either by damaging socket contacts or by allowing foreign objects to be inserted into the live openings. The FatallyFlawed website displays a statement from the socket-outlet manufacturer MK Electric, "MK goes to great lengths to ensure that all its BS 1363 plugs and sockets are safe. Inserting incorrectly dimensioned products into a socket-outlet can both damage the socket and reduce its safety".

Pin insulation

BS 1363 plug, with a plastic pin insulated shutter opening device (ISOD) and sleeved pins.

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. An early method of sleeving the pins involving spring loaded sleeves is described in the 1967 British Patent GB1067870. The method actually adopted is described in the 1972 British Patent GB1292991. Sleeved pins became part of the standard in 1984.

Other safety features

Internal wiring. Nº1 Cable grip; Nº2 Neutral terminal; Nº3 Earth terminal; Nº4 Line terminal; Nº5 Fuse

The plug sides are shaped to improve grip and make it easier to remove the plug from a socket-outlet. 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 earth wire breaks last.

Counterfeits

Counterfeit plugs and fuses not meeting the standard are commonly available. Legislation was introduced, with the 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. The pressure group PlugSafe reports that since August 2011 over 1000 listings of products including illegal plugs have been removed from the websites of ebay.co.uk and amazon.co.uk. The UK Electrical Safety Council has expressed shock at the magnitude of the problem and published a video demonstrating an exploding plug caused by a counterfeit BS 1362 fuse.

Fuses

BS 1362 fuses (for BS 1363 plugs)

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, which must conform to BS 1362. The role of the plug fuse is to protect the appliance flexible cord.

When the BS1363 plug was first introduced, there were 5 fuses in the official BS1362 range which were (with their specified colour): 2 (blue), 5 (grey), 7 (black) 10 (yellow), and 13 (brown) amps. The 7 amp fuse was deleted from the official range fairly early on, though remained available for many years along with many other sizes from 250 mA upwards. The current version, BS1362:1973, allows any fuse rating up to 13A, with 3 amp (coloured red) and 13 amp (coloured brown) as the preferred (but not mandated) values when used in a plug. All other ratings are to be coloured black (this is why 5 amp fuses are now black instead of grey). Plugs when supplied separately from any appliance should be available with either a 3 or 13 amp fuse fitted, but some are supplied with both (and a few also include the 5 amp size). The fuses are mechanically interchangeable; it is up to the end user or appliance manufacturer to install the appropriate rating. Some suppliers only supply plugs fitted with 13 amp fuses to save duplicating stock

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.

• For 3 A fuses: 0.02–80 s at 9 A, < 0.1 s at 20 A and < 0.03 s at 30 A.
• For 13 A fuses: 1–400 s at 30 A, 0.1–20 s at 50 A and 0.01–0.2 s at 100 A.

Replacement

Plugs for hand-wiring are commonly available and must be provided with instructions. They can be assembled or opened with a screwdriver. Most modern products come fitted with moulded plugs with removable fuse sections.

The secondary school syllabuses in the United Kingdom, Ireland, Hong Kong, Malaysia, and Singapore include the procedure for wiring BS 1363 plugs.

Folding plugs

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 unpolarised connector. In 2009 the ThinPlug received a "Red Dot" award for product design, the first products incorporating it are due to go on sale in June 2011. Another design concept, the Folding Plug, featuring a pivot which allows the plug's pins to be aligned vertically, won the Brit Insurance design of the year award in 2010, but as described in the promotional video it does not meet BS 1363, and has not been approved for sale in the UK as a plug. In 2012 a USB AC adapter was introduced with folding blades compatible with a BS 1363 socket-outlet.

• Folding plugs
• 
  The SlimPlug folding plug
• 
  The SlimPlug folding plug with pins retracted
• 
  The ThinPlug folding plug
• 
  The ThinPlug folding plug with earth pin folded

Variants

Several manufacturers have made deliberately incompatible variants for use where connection with standard plugs and socket-outlets 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.

The Walsall Gauge 13 A plug, which has each pin rotated 90°, was used by the BBC for technical power supplies, and socket-outlets for these plugs can be seen in some London Underground stations.

• Variant plugs
• 
  Walsall Gauge 13 A plug (bottom) compared to regular BS 1363 plug
• 
  Walsall Gauge 13 A plug
• 
  MK 13 A Plug with a T-shaped earth pin

Plug adaptors

Tripler (left) and doubler (right). The tripler has a red fuse carrier visible.

Plug adaptors permit two or more plugs to share one socket-outlet, or allow the use of a plug of different type. There are several common types, including double- and triple-socket blocks, shaver adapters, and multi-socket strips. Adaptors which allow the use of non-BS 1363 plugs, or more than two BS 1363 plugs, must be fused.

Doublers and triplers

BS 1363 allows doublers to be unfused and in practice fused doublers are very rare. Triplers are required to be fused.

Shaver adaptors

The purpose of these adaptors is to accept the 2 pin plugs of shavers, they are required to be marked as such. Shaver adaptors must have a 1 A BS 646 fuse. They must accept UK shaver plugs complying with BS 4573 and also Europlugs and American 2 pin plugs.

Conversion plugs

Conversion plug suitable for europlug, empty, europlug inserted and closed

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 socket-outlets. An example would be Class 2 appliances from mainland Europe which are fitted with moulded europlugs. Similar converters are available for a variety of other plug types. Unlike a temporary travel adapter, conversion plugs, when closed, resemble normal plugs, although larger and squarer. The non-BS 1363 plug is inserted into the contacts, and the hinged body of the conversion plug is closed and fixed shut to grip the plug. There must be an accessible fuse. Conversion plugs may be non-reusable (permanently closed) or reusable, in which case it must be impossible to open the conversion plug without using a tool.

The Plugs and Sockets, etc. (Safety) Regulations 1994 permit domestic appliances fitted with non-BS 1363 plugs to be supplied in the UK with conversion plugs fitted, but not with conversion plugs supplied for fitting by the consumer.

Connection units

Switched and unswitched fused connection units, without sockets, use BS 1362 fuses for connection of permanently wired appliances to a socket-outlet 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-outlet circuit, to protect spurs off a ring circuit with more than one socket-outlet, and sometimes to switch feeds to otherwise concealed socket-outlets for kitchen appliances.

Chronology

An early MK plug to original version of standard. Note the unsleeved Line & Neutral pins, and the inspection hole for the purpose of making the connection of an earth conductor visible with the cover in place (as required by BS 1363:1947 clause 15.)

BS 1363 is periodically revised, and with supplements and amendments issued between major revisions. BS 1363:1984 and earlier versions dealt only with 13 A plugs and socket-outlets. From 1989 onwards the standard was rearranged into five parts as follows:

• Part 1: Rewirable and non-rewirable 13 A fused plugs;
• Part 2: Switched and unswitched socket-outlets;
• Part 3: Adaptors;
• Part 4: 13 A fused connection units: switched and unswitched.
• Part 5: Fused conversion plugs

The following chronology shows revisions, supplements and significant amendments.

June 1947: BS 1363:1947 "Fused-Plugs and Shuttered Socket-Outlets" published.

May 1950: BS 1363:1947 Amendment 3, title changed to "Specification for two-pole and earthing-pin fused-plugs and shuttered socket-outlets for A.C. circuits up to 250 Volts (not intended for use on D.C. circuits)".

January 1957: BS 1363:1947 Amendment 5, added clause permitting operation of shutters by simultaneous insertion of two or more pins (in addition to original method using only earth pin).

January 1957: BS 1363:1947 Supplement No. 1 added specification for surface mounted socket-outlets.

1957: Complementary standard published, BS 2814:1957 "Two-pole and earthing-pin flush-mounted 13-Amp switch socket-outlets for A.C. circuits up to 250 Volts". A separate standard specifying a switched version of the BS 1363 socket-outlet for use with BS 1363 plugs.

December 1960: BS 1363:1947 Supplement No. 2, added specification for Resilient Plugs.

December 1961: BS 2814:1957 Amendment 2, title simplified to "13 Ampere Switch Socket-Outlets".

1962: BS 2814:1957 Supplement No. 1 added specification for surface mounted switch outlets.

September 1967: BS 1363:1967 "Specification for 13A plugs, switched and unswitched socket-outlets and boxes" published. This standard superseded both BS 1363:1947 and BS 2814:1957. Only 3A and 13A fuses are specified. Resilient Plugs are included.

August 1984: BS 1363:1984 "Specification for 13A fused plugs switched and unswitched socket-outlets" published. This standard superseded BS 1363:1967. Changes include introduction of sleeved pins on Line and Neutral, metric dimensions replacing inches, specifications added for non-rewireable plugs and portable socket-outlets. The standard was aligned, where possible, with the proposed IEC standard for domestic plugs and socket-outlets.

February 1989: BS 1363-3:1989 "13A plugs socket-outlets and adaptors - Part 3: Specification for adaptors" published. This new standard covers adaptors for use with BS 1363 socket-outlets and includes conversion adaptors (those which accept plugs of a different type), multiway adaptors (those which accept more than one plug, which may or may not be of a different type) and shaver adaptors. All adaptors (except for those accepting not more than two BS 1363 plugs) require to be fused. All socket-outlets, including those to other standards, must be shuttered.

1994: A Product Approval Specification, PAS 003:1994, "Non-Rewireable 13A Plugs with Plastic Socket Shutter Opening Pins" published. PAS 003 allowed for the design and approval of plugs without earthing intended for class II applications only.

February 1995: BS 1363-1:1995 "13A plugs socket-outlets adaptors and connection units - Part 1: Specification for rewireable and non-rewireable 13A fused plugs" published. This standard, together with BS 1363-2:1995, supersedes BS 1363:1984. The provisions of PAS 003 are incorporated, but the plastic pin is redesignated as an "ISOD"

September 1995: BS 1363-2:1995 "13A plugs socket-outlets adaptors and connection units - Part 2: Specification for 13A switched and unswitched socket-outlets" published.

September 1995: BS 1363-3:1995 "13A plugs socket-outlets adaptors and connection units - Part 3: Specification for adaptors" published. Supersedes BS 1363-3:1989

November 1995: BS 1363-4:1995 "13A plugs socket-outlets adaptors and connection units - Part 4: Specification for 13A fused connection units switched and unswitched" published. A new standard.

August 2008: BS 1363-5:2008 "13A plugs socket-outlets adaptors and connection units - Part 5: Specification for 13A fused conversion plugs" published. A new standard.

May 2012: BS 1363-1:1995 +A4:2012 (Title unchanged) published. This amended standard allows switches to be incorporated into plugs, and introduced new overload tests amongst others. BS 1363-1:1995 will remain current until 31 May 2015.

May 2012: BS 1363-2:1995 +A4:2012 (Title unchanged) published. This amended standard adds a requirement that it shall not be possible to operate a shutter by the insertion of a two-pin Europlug, and introduced new temperature rise tests amongst others. BS 1363-2:1995 will remain current until 31 May 2015.

May 2012: BS 1363-4:1995 +A4:2012 (Title unchanged) published. Minor changes to BS 1363-4:1995 which will remain current until 31 May 2015.

November 2012: BS 1363-3:1995 +A4:2012 (Title unchanged) published. This amended standard adds a requirement that it shall not be possible to operate a shutter by the insertion of a two-pin Europlug, and added specifications for switched adaptors amongst others. BS 1363-3:1995 will remain current until 31 December 2015.

References

• British Standard BS 1363: 13 A plugs, socket-outlets, adaptors and connection units
• British Standard BS 1362: General purpose fuse links for domestic and similar purposes (primarily for use in plugs). 1973.