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Old 7th Feb 2012, 3:39 pm   #73
emeritus
Dekatron
 
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
Default Re: Another unusual plug and some other questions

The string is not original. I didn't have any light-coloured wire handy and only used the string to show up the groove in the photo against the black bakelite of the plug.

I suppose it could have been used to attach it to a BC to 2 pin adaptor: 2 pin 5A plugs with captive 2 pin to BC adaptors were extensively used at a schoolfriend's house that in 1970 still had its original 2 pin 5A sockets in every room. I have a example myself, but the cord used is of far smaller size than the dimensions of the groove in my plug, and why is the end of the pin threaded? Earthed pendant lampholders are seldom found today other than in chandeliers, and I don't believe that it was normal practice to provide an earth at ceiling roses in pre-war installations. Older brass lampolders usually have no means of earthing the brass casing other than via the 1/2" tube that they are screwed on to, even if an earth were available.

Both the threaded pin and the other non-bayonet pin show evidence of having been cropped, no doubt so the plug would mate with a conventional shrouded lampholder. The shiny surface of the groove indicates that it was moulded and not ground out subsequently. There is no electrical connection between the threaded and the non-bayonet pin, and only the conventional pair of terminals in the interior of the plug.
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