Thanks to Johno12345 for the following:

Quote
This is another unusual British socket and plug. It is used for 240V clocks and is rated at 1A. It was often installed above the mantelpiece but this was removed from our reception area during refurbishment after the Sheffield
floods.

I believe that a 4 pin version existed for master/slave clocks also.

Someone might spot what is slightly odd about this example......


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