The BS546 UK standard
BS546 is the old British Standard for round pin plugs and sockets still found in UK and Ireland. Derived types are also found internationally.
The design originally dates from circa 1911, and was first codified into a formal standard as BS 73 in 1915, with later amendments. All these early types are unearthed. It should be noted that it was one of many competing designs, and the use of the word ‘standard’ does not mean it was of better quality, higher safety, or necessarily more official than others commercially available at the time.
In the year 1928 another standard was published, BS 317: Hand-shield and side entry three-pin wall plugs and sockets. Generally this added optional earthing to make 3 pin plugs and sockets.
The 1930 BS 372 (Side entry wall plugs and sockets for domestic purposes) brought both unearthed BS 73 and earthed BS 317 into the same unified standard.
Everything was finally standardised as BS546 in 1934, the current standard. The most recent edition of the standard is from 1950 and still remains in force: Two-pole and earthing-pin plugs, socket-outlets and socket-outlet adaptors for AC (50-60 Hz) circuits up to 250V. Despite technically being superseded by BS1363, it is still current and has been updated several times, most recently in 1999.
1931 image showing the size difference of the two BS372 plugs and example uses: 15A for an electric fire, and 5A for a vacuum cleaner.
Round pin sockets are nowadays only found in very old installations or specific applications. Plugs and sockets are generally identical, but scaled up across the 4 different sizes, to prevent interchangeability: larger old British plugs have higher current ratings. The earth pin on a lower rated plug is the same size as the line or neutral pins on the next bigger plug. For example, on a 5A plug the line and neutral are the same size as the earth of the 2A plug, whilst the (5A) earth is the same size as the line and neutral on the 15A plug.
The BS 546 standard only covers 3-pin plugs (older standards included 2-pin) and the triangular position of the pins provides polarity. Quite often the line and neutral pins are partially insulated to limit the risk of shock from a partially-inserted plug. The plugs have a small aperture at the top to check the earth wire has been connected, which dates from when grounding was not widespread. This requirement has been removed from BS 1363, but has remained in BS 546 for unknown reasons.
BS 546 sockets must have safety shutters, which may pose a problem for now-deprecated 2-pin plugs (which may not be compatible anyway). The need for safetly shutters is increasingly apparent as the higher rated socket outlets have larger apertures; this may not be the case in other similar standards based on BS 546. Sockets may have switches, but this is not a requirement.
BS 646 fuses were included in the standard since the 1934 edition but are very rare. Due to needing more space inside them for the fuse, fused BS 546 plugs can be recognised by their generally square rather than triangular shape. There were only 2A and 5A fuses; 15A was deemed unnecessary inside the plug as the fuseboard already had a 15A fuse. In fact one of the common reasons to use BS546 is to remove the fuse found in BS 1362 plugs, often the case in theatres and lighting.
BS546 standard
BS546 2A UK plug
The smallest plug and socket, the UK 2A plug is only used for individual lights, both historically and today. It is used reasonably rarely, so is not often seen. In fact, the plug is so small as to sometimes make assembly problematic on any but the smallest cables. Pin diameters: earth 0.140 in, line and neutral 0.200 in.
We only stock these as rewireable plugs in white and black.
BS546 5A plug
The next size up, the 5A UK plug, was historically used for small appliances. Nowadays the main function is for lighting on a specific circuit, and in hotels to prevent unauthorised use of the sockets. Pin diameters: earth 0.200 in, line and neutral 0.278 in. Without the earth pin it is the basis for the 0.2A BS 4573 shaver plug used for power in bathrooms. The specification is also the basis of Indian IS 1293 and South African SANS 164-3 standards, both of which changed the units of measurement from inches to millimetres, and increased the current rating to 6A.
We hold these as rewireable plugs in black and white, plus on moulded mains leads to Indian standards.
BS546 15A plug
The largest size domestic plug, the UK 15A plug was used for normal and larger appliances in the past. Current usage is for lighting, especially in theatres and large buildings, although this use is recently decreasing; another use is sometimes in shops for point of sale or other equipment. Pin diameters: earth 0.278 in, line and neutral 0.343 in. It is the basis of Malaysian standard MS 1577 and Singapore’s SS 472.
South Africa and India also used it for SANS 164-1 and IS 1293 respectively, but also changed dimensions to metric and the current rating from 15A to 16A. The UK used adaptors to use the smaller 2A and 5A plugs in the larger 15A sockets, but India has multi-sockets that accept both 6A and 16A plugs.
We stock these in white and black, plus black/transparent to South African specification. We also hold them as moulded power cables in black to both Indian and South African spec.
BS546 30A
The largest of the series, reserved for very high current appliances such as domestic cookers and ovens, or industrial equipment and machines. These plugs and sockets were almost always waterproof, with inline plugs and connectors that screwed together to provide a seal. Pin diameters: earth 0.312 in, line and neutral 0.375 in. They are very rare now as they have long been replaced by IEC 60309. IEC 60309, previously IEC 309, and before that BS 4343, was actually based on the BS546 standard and uses the same diameter pins, but with different spacing and much longer lengths making them funtionally incompatible.
We do not hold these in stock.
Some non-standard BS 1363 plugs use one pin from a BS546 plug to make them not interchangeable.
Please contact us for pricing and advice on any of these parts. We only stock BS546 plugs as rewireables in black and white and 2A, 5A and 15A: we can’t supply 30A. For moulded we can only supply the Indian or South African standard
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