Re: Another unusual plug and some other questions
AFAIK Britmac and Dorman & Smith were unrelated at the time although they are now both under the Electrium banner along with Wylex and others (or is it now a Tyco brand?). The Wandsworth plug with automatic switch operation, that I mentioned above, is also unrelated to the DS. It was made by Wandsworth Electrical Ltd and available in the early 30's. Your MK interlocked type is probably mid 20's - early 30's. They are listed in Sunco 1929 but by 1936 MK seem to have been changing to BS gauges for interlocked types. The 15A is then described as having an earth pin 'not grooved or mutilated in any way.'
The non-BS and interlocking types are rare now, I am working on collecting a comprehensive assortment but with some difficulty. The last time I used Wandsworth was in 2002, in an old hall with wiring from the 1920s that had never been inspected or tested since. DS was in use for tech supplies at the BBC until fairly recently. Below are some mobile phone pics of related catalogue pages. Unfortunately I don't have any examples of either type of plug to hand to reveal the constructional details.
The sharp-eyed reader will have spotted a mistake in my earlier post where I typed 'Wandsworth gauge' instead of 'Walsall Gauge' when referring to the variant-BS1363 with reversed pin orientations.
Lucien
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