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See also the entry in the mains power plug article on the British three-pin plug.
A BS 1363 plug has two horizontal, rectangular pins for live and neutral, and above these pins, a larger, vertical pin for an earth connection. Unlike many other plugs, the earth pin is mandatory as it is needed to open the shutters. It also polarises the plug. Moulded plugs for unearthed, double-insulated appliances can substitute this contact with a plastic pin.
These plugs are required to carry a cartridge fuse, manufactured to BS 1362, which can be rated at 3, 5, 10 or 13 amperes. The maximum load that can be placed on a socket, including double and triple sockets, is 13 amps. The double sockets are unfused, so it is possible to draw up to 26 amps before hitting the rated current of any overcurrent protection. However when drawing up the standard it was decided to only require double sockets to be able to take 13A total!. Most sockets can stand more than this at least in the short term but continuous running at 26A WILL result in a damaged socket. Surprisingly however this has not posed a problem in practice probably because of the fact that very few domestic appliances draw the full 13A for any significant time. Triple and larger sockets are fitted with a 13 amp fuse of the same type used in the plugs.
The plugs and sockets are designed to carry up to 250 volts AC, 50 hertz. The UK power system is officially 230V +10% -6%. However, in reality, voltages are generally closer to 240 volts than 230, as the old standard before European harmonisation was 240V +-6%, and most supplies installed to the old standard meet the new standard.
This plug is often referred to as the safest in the world and to many outsiders it often seems excessively safety conscious and somewhat clunky to those not familiar with it. The high extraction force can be inconvenient, particularly to people with weak hands, such as the elderly. To counter this plugs with handles and traps to fit existing plugs and provide a handle have been produced but never really caught on. The large size can make the plugs inconvenient when there are many plugs in a small space, as on extension strips.
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All plugs with the exception of a few wall warts are fused. This is in addition to fuse boxes or circuit breakers in houses. This is done for two reasons: First, to better protect different types of appliance, and second, to allow high current 32A socket circuits to be used safely. These circuits are usually but not always in the form of ring final circuits (informally known as ring mains). Fuses for fittings to BS 1363 must conform to BS 1362. This specification describes a sand-filled ceramic bodied fuse, 1" in length and 1/4" in diameter.
British power outlets incorporate shutters on the live 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 wall warts 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 live and neutral pins and does not depend on the earth pin. Some older sockets simply require equal pressure to be placed upon the live and neutral shutters (towards the outer edges so as to stop insertion of 4mm 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. 4mm pin European plug types (CEE 7/16, Gost 7396) will fit in after doing this and 4.8mm 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 30A or 32A fuse or breaker (which is much higher than the wiring regs permit for other non industrial socketIndustrial power plug is used here to refer to those power connectors that, unlike mains power plugs, are not used for the average domestic appliance but rather for more heavy-duty applications such as arc welders, cranes, cinemas, large cooking ranges et types) means this is not recommended.
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