BS 546 - AbsoluteAstronomy.com

BS 546 is a pre-Second World War British Standard for domestic AC power plugs and sockets

Domestic AC power plugs and sockets

AC power plugs and sockets are devices for removably connecting electrically operated devices to the power supply. Electrical plugs and sockets differ by country in rating, shape, size and type of connectors...

that is also the precursor of current Indian and South African plug standards. This plug is also used in Singapore to a limited extent. 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 6 different versions that are not interconnectable. Whilst these sockets are no longer used in Britain for general appliances (although still permitted by the UK wiring regulations

BS 7671

British Standard BS 7671 "Requirements for electrical installations" is the national standard in the United Kingdom for low voltage electrical installations....

), some of the varieties remain in use in other countries and in more specialist applications (a notable example being stage lighting). The current edition of the standard was issued in 1950, with supplements since issue.

Prior to the development of the BS 546 standards there were around two dozen different types of power socket in use throughout Britain with different types in use in different cities.

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 from 15 A down to 5 A and from 5 A down to 2 A so in practice it was quite possible for an appliance with the smallest size of flex to be protected only by a 15 A 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

BS 1363

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...

fused plug that replaced them. Fused BS 546 plugs using a BS 646 fuse are available but are rarely seen in practice.

In theory, 15 A plugs were to be used for larger appliances such as electric heaters, while smaller appliances such as radios or table lamps were supposed to use 5 A. In practice this was found to be inconvenient, and in many households the 15 amp plug was used for everything. Adaptors were available which allowed 2 or 5 amp plugs to be used in 15 amp sockets.

The 3-pin sockets were not shuttered when BS 546 was in common use domestically in the UK. The current revision of the standard does specify shutters similar to those of BS 1363

BS 1363

. Current UK wiring regulations require socket outlets installed in homes to be shuttered. The three pin variety had the larger top pin as the earth connection, the left hand pin as neutral and the right hand pin as live http://www.irishstatutebook.ie/1987/en/si/0172.html (when looking at a socket or at the rear of a plug).

The three pin 2 A, 5 A, and 15 A, connectors of BS 546 are duplicated by Group B1 of the GOST 7396 standard.

2 A 2 pin

This plug did not find general use and is now rarely seen. It was incompatible with the 2 A 3 pin variant by variation of the pin gauge and this may have contributed to its lack of adoption.

5 A 2 pin

This plug became the UK standard shaver plug (BS 4573) and is similar but slightly larger than the Europlug

Europlug

The Europlug is a flat, two-pole domestic AC power plug that is generally supplied moulded on the end of an appliance's flex or a power cord, designed for voltages up to 250 V and currents up to 2.5 A...

(and the pins are only 16mm apart). British shaver sockets and adaptors tend to be sized to accept this, Europlugs and two pin American and Australian plugs.

2 A 3 pin

This plug was used to connect low power appliances (and to adaptors from the larger socket types). It is sometimes still used to connect lamps to a lighting circuit.

5 A 3 pin

This plug was used for moderate sized appliances, either on its own 5 A circuit or on a multi socket 15 A circuit, and also on many adaptors (both multi socket 5 A adaptors and adaptors that also had 15 A pins). Some 5 A 3 pin sockets also have two extra holes above the live and neutral holes to allow a 5 A 2 pin plug to be connected.

India has standardised on this plug as Indian Standard IA6A3, rated at 6A / 250V, and it is now almost exclusively used in India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, Sri Lanka

Sri Lanka

Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...

, Nepal

Nepal

Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...

and Namibia

Namibia

Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...

. This 5 A plug, along with its 2 A cousin, is sometimes used in the UK

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

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 15 A model below.

15 A 3 pin

This is the largest plug in domestic use. Live and neutral are spaced 1 inches (25.4 mm) apart, and earth is 1+1/8 in away from each of them. The 15 A version is also used in Pakistan

Pakistan

Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

, India

India

, Sri Lanka

Sri Lanka

, Nepal

Nepal

, and Namibia

Namibia

for larger appliances. In India it is rated at 16 A under Indian Standard IA16A3. Some countries like South Africa

South Africa

The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

use it as the main domestic plug and socket type as South African standard SABS 164. Sockets almost always have an on–off switch built into them. This type is almost universally used in the UK for indoor dimmable theatre and architectural lighting installations, and for centrally controlled sockets. Fused plugs 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

Israel

The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

, Malaysia and Singapore

Singapore

Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...

for air conditioners

Air conditioning

An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

and washing machines.

30 A 3 pin

The 30 A plug is the largest of the family and is slightly larger than the 15 A plug. This was used for high power industrial equipment up to 7.2 kW, such as industrial kitchen appliances, or dimmer racks for stage lighting. Plugs and sockets were usually of an industrial waterproof design with a screw locking ring on the plug to hold it in the socket against waterproof seals, and sockets often had a screw cap chained to them to be used when no plug was inserted to keep them waterproof. Use of the BS 546 30 A plugs and sockets diminished through the 1970s as they were replaced with BS 4343 (which later became IEC 60309) industrial combo plugs and sockets.

Characteristics of BS 546 plugs

	type ? 30A	type M 15A	type D 5A	type ? 2A
Diameter L and N pins	7.92 mm	7.06 mm	5.08 mm	3.56 mm
Diameter earth pin	9.53 mm	8.71 mm	7.06 mm	5.08 mm
Centre distance between L and N pin	36.50 mm	25.40 mm	19.05 mm	14.48 mm

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