BS 546
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BS 546 is an old British Standard for domestic AC power plugs and sockets.They are also known as type D (for the 5A 3 pin) and type M (for the 15A 3 pin) in US documentation. When viewed in photographs with no indication of scale, the different ratings look similar but where a photograph shows more than one type the difference in size is obvious. There are 5 different versions that are not interconnectable. Whilst these sockets are no longer used in Britain for general appliances some of the varieties remain in use in other countries and in more specialist applications.
15A sockets were generally given a dedicated 15A circuit. 5A sockets might be on a 15A circuit with multiple sockets or on a dedicated 5A circuit. 2A sockets were generally connected to the lighting circuit which was fused at 5A. Adaptors were available from 15A down to 5A and from 5A down to 2A so in practice it was quite possible for an appliance with the smallest size of flex to be protected only by a 15A fuse. This is a similar level of protection to that seen for portable appliances in other countries but less than that offered by the BS 1363 fused plug that replaced them. Fused BS 546 plugs using a BS 646 fuse are available but are rarely seen in practice.
The 3 pin sockets were not shuttered when BS546 was in common use domestically in the UK but the current revision of the standard does specify them and BS 546 sockets sold in the UK today are shuttered in the same basic manner as BS 1363 ones..
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[edit] 2A 2 pin
This plug did not find general use and is now rarely seen. It was rendered incompatible with the 2a 3 pin variant by variation of the pin gauge and this may have contributed to it's lack of adoption.
[edit] 5A 2 pin
This plug is what became the UK standard shaver plug and is similar but slightly larger than the Europlug. British shaver sockets and adaptors tend to be sized to accept this, Europlugs and two pin American and Australian plugs.
[edit] 2A 3 pin
This plug was used to connect low power appliances to the lighting circuit (and to adaptors from the larger socket types). Sometimes still used to connect lamps (and other lights which aren't attached, or built-in to the fabric of the building - e.g. lights which are mounted on kitchen cabinets, bookshelves etc.) to the lighting circuit but shuttered 2A sockets are rare and unshuttered sockets are not supposed to be used anymore in the UK but can still be found in older buildings.
[edit] 5A 3 pin
This plug was used for moderate sized appliances either being on its own 5A circuit or a multi socket 15A circuit and also on many adaptors (both multi socket 5A adaptors and adaptors that also had 15A pins). Some 5A 3 pin sockets also have 2 extra holes above the live and neutral holes to allow a 5A 2 pin plug to be connected.
India has standardised on this plug and is now almost exclusively used in India, Sri Lanka, Nepal and Namibia. However, this 5A plug, along with its 2A cousin, is sometimes used in the UK for centrally switched domestic lighting circuits, in order to distinguish them from normal power circuits. This is quite common in hotel rooms. This plug was also once used in theatrical installations for the same reasons as the 15A model below, but is now only used for this purpose in schools and other rarely used installations (presumably because those operating multiple installations wanted to standardise on one plug type for all their lights and the 5A plug was unsuitable for larger lights).
[edit] 15A 3 pin
This is the largest version with live and neutral spaced 1 inch apart, and earth is 1⅛ inches away from each of them. Although the preceding type is standard in India, Sri Lanka, Nepal, and Namibia, the 15A version is also used in these countries for larger appliances. Some countries like South Africa use it as the main domestic plug and socket type, where sockets almost always have an on–off switch built into them. The Type M is almost universally used in the UK for indoor dimmable theatre and architectural lighting installations. It is also often used for non-dimmed but centrally controlled sockets within such installations. The main reason for doing this is that fused plugs, while convenient for domestic wiring (as they allow 32A socket circuits to be used safely), are not convenient if the plugs and sockets are in hard to access locations (like lighting bars) or if using chains of extension leads (since it is hard to figure out which fuse has blown). Both of these situations are common in theatre wiring. This plug is also widely used in Israel for air conditioners.
