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BS 1363
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British Standard BS 1363 specifies the most common type of domestic AC power plugs and sockets that are used in the United Kingdom, Cyprus, Ireland, Malta, Malaysia, Singapore and many former British colonies. Of these, Ireland, Malaysia and Singapore have equivalent standards - IS 401 & 411, MS 589 and SS 145 respectively. In these countries, the system is colloquially also known as the 13 amp plug/socket. Other plug types used in the same area include IEC 309, only used in industrial and some outdoor applications, and BS 546, limited to old installations and specialised applications where either the BS 1363 plug is unsuitable or where mateability with the standard variety is not desired e.g.
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British Standard BS 1363 specifies the most common type of domestic AC power plugs and sockets that are used in the United Kingdom, Cyprus, Ireland, Malta, Malaysia, Singapore and many former British colonies. Of these, Ireland, Malaysia and Singapore have equivalent standards - IS 401 & 411, MS 589 and SS 145 respectively. In these countries, the system is colloquially also known as the 13 amp plug/socket. Other plug types used in the same area include IEC 309, only used in industrial and some outdoor applications, and BS 546, limited to old installations and specialised applications where either the BS 1363 plug is unsuitable or where mateability with the standard variety is not desired e.g. where lamps are controlled by a switch/dimmer.
Trading standards legislation in both the UK and Ireland requires that all normal electrical goods sold in either country should be fitted with a BS 1363 / IS 401 plug.
A BS 1363 plug has two horizontal, rectangular pins for phase (commonly termed 'live') and neutral, and above these pins, a larger, vertical pin for an earth connection.
Unlike with 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 live and neutral pins to be inserted. It also polarises the plug, ensuring that the live pin is connected to the correct terminal in the socket. Moulded plugs for unearthed, double-insulated appliances may substitute this contact with a non-conductive plastic pin to open the shutter. Most non-fixed domestic equipment is connected using the BS 1363 plugs, the main exceptions being equipment requiring more than 13 amperes (e.g. larger electric cookers, which are hard-wired), remotely switched, non-fixed lighting (which use proprietary or BS 546 plugs), 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.
Because typical British circuits (especially ring circuits) can deliver more current than many appliance power cords can safely handle, BS 1363 plugs are required to carry a cartridge fuse. The fuse is manufactured to BS 1362 and are normally rated at 3, 5, 10 or 13 amperes. 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 plugs and sockets are designed to carry up to 250 volts AC, 50 hertz. For information on the safe installation of BS 1363 sockets, see the article on Electrical wiring (UK).
The requirement for sockets to be child safe and include a shutter mechanism dates back to a remarkable and far-sighted wartime committee which resulted in the publication of ‘Post War Building Study No. 11 – Electrical Installations’ in January 1944. In 1947 there followed, as a result of this initiative, "British Standard 1363 : 1947 FUSED PLUGS AND SHUTTERED SOCKET OUTLETS". See this article from the IET
This plug is could be described as one of the the safest in the world and to many outsiders it often seems excessively safety conscious and unduly large. The high extraction force can be inconvenient, particularly for people with weak hands, such as the elderly (plugs with handles, and straps to provide existing plugs with a handle, have been produced but have not been popular). Most wall sockets have built-in switches, reducing the need for plug removal when power is not required. The switch is just for convenience, and is not a regulatory requirement. The large size can make the plugs inconvenient when there are many plugs in a small space, as on power strips. On the other hand the side entry flex (cable) gives the combination of plug and flush socket a low profile to the wall (which is useful if plugging something in behind a cupboard, for example).
Origins
This style of plug appeared in 1946, shortly after the Second World War. Britain had previously used a combination of 5 Amp and 15 Amp round pin sockets where each had to be wired to the distribution board and each provided with its own fuse. As a result of high wartime demands, Britain suffered from a chronic shortage of copper. Further, as a result of enemy action a considerable amount of housing stock had been destroyed. Britain was in the position of having to rapidly rebuild housing for its population and electrically wire it using as little copper as possible.
The solution was the ring main system where instead of each socket being individually wired, a cable was brought from the fuse or circuit breaker in the distribution board and wired in sequence to a number of sockets before being taken back to the distribution board and wired to the same fuse or circuit breaker. This provided considerable savings in the copper required to wire the circuit. Since the fuse or circuit breaker had to be rated for the maximum current the ring could carry (30A or 32A for breaker), it was required that the plugs used to connect to the ring each contained their own fuse rated for the appliance that it connected. At first there were several competing designs of plug, but the BS 1363 design displaced all of the others.
Although the need to economise on the use of copper has long passed, the ring main system has proven so successful that Britain retains the system to this day, even in new build houses.
Fuses were originally available in 1, 2, 3, 5, 7, 10 and 13 Amps but by the 1960s this range had reduced to 2(blue), 5(grey), 10(yellow) and 13(brown) Amps. Plugs are normally supplied fitted with a 13A fuse, and householders tended not to replace them with a more appropriate size. Eventually the range was officially reduced to just 3(red) and 13(brown) Amps. 5 Amp fuses have remained freely available, but are coloured black (which does not denote a 5 Amp fuse but an unofficial size) and may be used for appliances that draw a large current at switch-on, but a lower steady load (for example older CRT TV sets). Other fuse sizes remain available albeit hard to find.
Safety measures
Fuses
All plugs with the exception of some plug top power supply units are fused. This is in addition to the fuses or circuit breakers in consumer units/distribution boards.
Prior to the introduction of the 13 amp plug the BS 546 2 A, 5 A and 15 A plugs were used. With this system the only fuses were in the consumer unit. 15 A sockets were generally given a dedicated 15 A circuit. 5 A sockets might be on a 15 A circuit with multiple sockets or on a dedicated 5 A circuit. 2 A sockets were generally connected to the lighting circuit which was fused at 5 A. Adaptors were available to use 5 A plugs in 15A sockets, and from 2A plugs in 5 A sockets, so it was quite possible for an appliance with the smallest size of flex to be protected only by a 15 A fuse.
When the practice of using 30 A ring circuits was introduced (to save copper whilst also allowing more flexibility) it was considered unsafe to allow appliance flexes to be connected to such a high rated circuit with no further protection, and the plug/socket combination had to provide the fuse. It was decided to place the fuse in the plug, and to use a new plug configuration so that older unfused plugs could not be used.
Putting the fuse in the plug also allows a range of ratings to be fitted providing superior protection for smaller flexes. This is especially useful for long small flexes or for extension leads that are not rated at the full 13A. Fuses for fittings to BS 1363 must conform to BS 1362. This specification describes a sand-filled ceramic-bodied cylindrical fuse, 25.4 mm (1") in length, with two metallic end caps of 6.3 mm (1/4") diameter and 5.5 mm long.
BS 1362 specifies breaking-time/current characteristics only for fuses with a current rating of 3 A (marked in red) or 13 A (marked in brown). Examples for the required breaking-time ranges are
- 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.
3 A fuses are intended mainly for small load (< 750 W) appliances, such as radios and lights. 13 A fuses are for larger load (<3.2 kW) appliances such as heating and heavy-duty electric motors.
BS 1362 requires that plug fuses with any other current rating are marked in black. 5 A fuses are also commonly used, for medium load (1250 W max.) appliances such as desktop computers and TV sets. Ratings of 1, 2, 7 and 10 amperes are also produced, but rarely used (1 A as found in some shaving-socket adapters is 20mm long (BS 646) but a BS 1362 version does exist.).
The fuses are mechanically compatible; it is up to the user or appliance manufacturer to use the most appropriate rating.
Rewirable BS 1363 plugs are always sold fitted with a fuse, usually 13 A. This fuse must be changed if fitting the plug to an appliance or flex which requires a fuse with a smaller rating. Plugs with smaller fuse sizes already fitted are sold but are not as common.
Shuttering
British power outlets incorporate shutters on the phase and neutral contacts to prevent someone from pushing a foreign object into the socket. On most sockets these are opened by the earth pin which is longer than the others and must always be present (though on Class 2 (double insulated) equipment with moulded-on plugs or euro converter plugs (see later) and on class 2 power supply units it may be plastic). A notable exception to this method of opening shutters are sockets made by MK. These use a proprietary system which seems to depend on the shape of the phase and neutral pins and does not depend on the earth pin. Some older sockets simply require equal pressure to be placed upon the phase and neutral shutters (towards the outer edges so as to stop insertion of 4-mm plugs). On sockets which use the earth pin to open the shutters, said shutters can be opened by inserting an object into the Earth hole (a screwdriver works well for this). Electricians do this frequently to allow them to insert test probes into sockets. The 4-mm pin European plug types (CEE 7/16, GOST 7396) will fit in after doing this, and 4.8-mm ones (CEE 7/4, 7/7 or 7/17) will go in if forced. However the lack of earth connection (if the plug has it) and the fact that BS 1363 sockets will often only be protected by a 30 A or 32 A fuse or breaker (which is much higher than the wiring regulations permit for other non-industrial socket types) means this is not recommended. Despite the built-in shuttering there is a widespread but false perception that objects can be inserted into sockets, and there are many "safety socket covers" available which pander to this. Unfortunately these plug-in devices serve as ideal means to disable the internal shutters (when plugged in upside down) and result in decreasing safety, not improving it. Some of the most popular types on the market actually allow objects such as paper clips to be inserted alongside the line pin of the socket cover. The campaign was founded in August 2008 to raise awareness of this issue.
Pin insulation
The phase and neutral pins on modern plugs have insulated bases to prevent finger contact with pins and also to stop metal sheets (for example, fallen blind slats) from becoming live if lodged between the wall and a partly pulled out plug. A downside to this prong insulation is that it may contribute to damaged sockets not making good contact with the prongs, which may even melt the latter. No such problems exist with healthy sockets.
Dimensions
The live 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 centred on the symmetry plane, is 22.73±0.5 mm long and has a cross section 3.975±0.075 mm wide and 7.925±0.125 mm height. The centre lines of the live/neutral pins and the protective pin are vertically 22.23±0.13 mm apart.
(These dimensions may be more easily remembered in the original imperial units, which are not mentioned in the current standard: 1/4±0.005 inch wide by 5/32±0.0025 inch high, and 0.695±0.02 inch long. They are 7/8±0.005 inch horizontally from each other, and the same distance vertically from the earth pin, which is 0.895±0.02 inch long. The pin lengths were presumably originally 0.7 and 0.9 inches, and assigned an asymmetric tolerance of +0.005/-0.015.)
Others
- The plug base is broadened near the pins to help keep fingers away from the pins (this was a very early modification to the standard, which was later improved by the use of the insulated pin bases described above).
- The plug sides are shaped to improve grip and make it easier to remove the plug from a socket without placing fingers behind the plug where the pins are.
- The plug is polarised, so that it cannot be inserted with the phase and neutral pins reversed. This feature is important to make sure the fuse is in the phase side of the supply.
- The cable always enters the plug from the bottom, thus making it difficult for people to unplug the (quite firmly fitting) plug by tugging on the cable. This practice — possible with many other plug designs — can be hazardous as it can damage the cable insulation causing shorts or tear the conductors, leading to overheating or even internal arcing across the resulting break in the conductor. On the other hand this tight fitting and bottom entry of cable means that the stresses on the cable when it is pulled hard (by for example tripping over it) are even higher.
- The plug is firmly fitting and therefore difficult to dislodge by accidental knocks or strains on the cord
- The design of the earth pin ensures that the earth path is connected before the live pins, and remains connected after the live pins are removed.
- The design of the earth pin being of a larger dimension prevents it from being inserted into the phase or neutral sockets should this be attempted in error
- Should the cable be tugged from the plug, the designed lengths of the internal wires should mean that the live wire is disconnected first, followed by the neutral and finally the earth. This ensures that an abused plug will fail safely.
Replacement
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 flat-head and/or cross-head screwdriver - modern plugs often have external screws which accommodate both types but the terminal screws inside are more often flat-headed; the cross-head and combination screw-heads tend to be made to accommodate Pozidriv rather than Phillips screwdrivers but this varies between manufacturers. Most modern products come fitted with moulded plugs with removable fuse sections (these plugs can only be easily removed by cutting off), with some exceptions such as most lamps which usually have normal hand-wired plugs along with a label with wiring instructions wrapped around the flex.
The secondary school physics syllabuses in England and Wales, Northern Ireland, Scotland, Ireland and Hong Kong 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).
Euro converter plugs
Some manufacturers/distributors use a special type of plug for conversion of Class 2 appliances from mainland Europe which are fitted with moulded europlugs. Unlike a travel adaptor these plugs when closed look fairly similar to normal plugs, although larger and squarer. Inside are two metal clips into which the metal ends of the europlugs pins are clipped. The body of the converter plug is shaped to grip the europlug. The hinged lid is then shut to cover the connections to the europlug and is screwed shut. These plugs have a plastic earth pin and a fuse accessible from the outside and in some cases 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.
These adaptors are usually supplied fitted on all recent Class 2 Sony electrical products with fixed wiring (and not IEC C7 cables) sold in the British Isles instead of typical moulded plugs, probably as a measure to reduce costs by fitting the same plug for all European markets .
Countries of use
This design is not only in use in the United Kingdom and Ireland, but also in Sri Lanka, Bahrain, UAE, Qatar, Yemen, Oman, Cyprus, Malta, Gibraltar, Botswana, Ghana, Hong Kong, Macau, Brunei, Malaysia, Singapore, Kenya, Uganda, Nigeria, Iraq, Tanzania 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 230v installations although 110V installations using the NEMA connector are more common.
In the Republic of Ireland 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 Republic, must pass the Irish Standard or an equivalent standard of a member of European Union, which includes BS 1363.
The UK, and some of these other countries, also use the older BS 546 round-pin socket standard.
In some continental European countries (e.g., Germany), the BS 1363 system is today often used for low-voltage (12 V or 24 V) DC connections in photovoltaic systems, because it provides easily available high-current connectors with fixed polarity that cannot accidentally be connected into higher-voltage schuko system and europlug sockets.
Variants
Several manufacturers have made deliberately incompatible variants for use where intermatability with standard plugs and sockets is not acceptable. Examples include filtered supplies for computer equipment and cleaners' supplies in public buildings/areas (to prevent visitors plugging things in). The most commonly seen variant is one made by MK which has a T-shaped earth pin.
The Walsall Gauge 13 A plug was used by the BBC for technical supplies and sockets for these plugs can be seen in some London Underground stations.
In 2006, a British company, Ridings Ltd, invented a folding British BS1363 plug, called the
. This was granted a and is the to be granted an approval to BS1363.
Other devices covered by BS 1363
As described above, BS 1363 specifies 13 A plugs and sockets. It also specifies the following devices:
- Adaptors, which permit two or more plugs to share one socket.
- Switched and unswitched fused connection units, which take the same BS 1362 fuses as the plugs. These are the standard means of connecting permanently wired appliances to a socket circuit (most often but not always a 30 A ring circuit). They are also used in other situations where a fuse and/or switch 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 (20 A DP switches are also sometimes used for this but doing so can easily violate the rule of no more non-fused spurs than sockets on the ring).
See also
Footnotes
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