Museum of Plugs and Sockets logo, small Bayonet Cap (B22d-2)
BS 52 sockets, plugs and adapters
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BS 546
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 phased out


Use of bayonet sockets and plugs.

BS 52 gives specifications for  bayonet lamp-caps lampholders and B.C. adapters (lampholder plugs).
Originally bayonet sockets were used in the UK for 'lighting', whereas BS 546 sockets were meant for applications that needed more 'power'.
Lighting and Power were charged for different tariffs.
Depending on the tariffs it could be attractive to plug an electric iron into a light socket. Because bayonet sockets have no earth connection it was a dangerous method of saving money. Information given by David Fisher.

However, lighting tariff was not always the lowest rate.
Gareth Foster has found a notice of the London Electricity Board, informing customers that:
"The following Tariff will come into operation in respect of electricity consumed after the first meter reading following June 30th, 1948.
   Rate 1A: LIGHTING  2 d. per unit.
   Rate 2A: HEATING AND COOKING  1 d. per unit.
   Rate 3A: POWER  1 d. per unit."
An alternative reason for using light sockets is a lack of sufficient sockets. A light socket above the dinner table is also convenient for connecting a toaster or kettle.


Bayonet lampholder with 5A 2pin outlets Bayonet adapter with swich BC lighting plug Bayonet Cap plug

BC plug, exploded view

1 B22d-2* bayonet lamp holder with two BS 372 Part I outlets.   {JM}
* B = Bayonet; 22d = diameter in mm; 2 = double contacts. This type is also known as BC = Bayonet Cap.
Brand name: Anchor, a large Indian plug, socket and switch manufacturing company. Bayonet light bulb mounts are the standard fitting in - among others - India and Bhutan. India uses plugs according to IS 1293, which is derived from BS 546.
2 Two-way BC adapter with switch (red knob). The star with BG is an older type of logo used by the company British General.
3 BC lampholder plug complying with BS 52 standard. The plug fits in a B22 bayonet lamp holder (see nos. 1 and 2).   {DF}
4, 5 BC adapter plug that is composed of two parts: an outlet that fits in a B22d-2 lamp holder (bottom right) and a standard 2-pin 5A BS 372 Part I plug (bottom left). Instead of this plug each other 2-pin 5A, or shaver plug can be used. Image no.5 shows and exploded view of this ingenious device.   {DF}

Bayonet cap adapter plug with variable pin spacing
Bayonet cap adapter plug with variable pin spacing

6, 7 Adapter plug with two pins (5 mm diameter) which spacing is adjustable between 15 and 24 mm. Pins are connected to a B22d-2 bayonet outlet. The adapter fits a variety of outlets, but it is questionable whether sockets have existed that could accept the adapter with 5 mm pins positioned only 15 mm apart. Characteristics of BS 546 plugs/sockets are given on the BS 546 main page.
The adapter has been designed by The General Electric Company Ltd, London and William Manchester of Union Works, North Wembley, Middlesex. U.K. Patent no. 251068-A for 'An improved electric connector or adapter' was published on April 29, 1926. {PC}


Find more examples of bayonet cap material on the page devoted to classic South African plugs and sockets.


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BS 546
D i g i t a l   M u s e u m   o f
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P l u g s   a n d   S o c k e t s
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Bayonet lamp