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Old 30th Jan 2019, 8:37 am   #1
Karen O
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Default Why the hole in the top of old 13A plugs?

For years I've seen 13A plugs which have a hole in the top, providing access it seems to the Earth terminal. I've not noticed this in modern times.

What was all that about?
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Old 30th Jan 2019, 9:01 am   #2
Dave Moll
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Default Re: Why the hole in the top of old 13A plugs

I seem to recall that this has been discussed before on this forum, but I can't think what to search for to find the thread.

Although it was often used for attaching an earth lead separate from the (usually two-core) mains flex, I seem to recall that this was stated not to be the purpose. What I don't remember is the purpose stated then.
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Old 30th Jan 2019, 9:27 am   #3
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Default Re: Why the hole in the top of old 13A plugs

https://www.vintage-radio.net/forum/...ad.php?t=88778

Post no. 56
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Old 30th Jan 2019, 10:05 am   #4
Karen O
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Default Re: Why the hole in the top of old 13A plugs?

Thanks - my curiosity is sated
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Old 30th Jan 2019, 10:36 am   #5
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Default Re: Why the hole in the top of old 13A plugs?

It isn't limited to 13A ring-main plugs. I've seen it on 5A & 15A types.
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Old 30th Jan 2019, 10:44 am   #6
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Default Re: Why the hole in the top of old 13A plugs?

Thank you to snowman al for pointing to the thread of which I was thinking and the stated purpose of the hole.
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Old 30th Jan 2019, 11:31 am   #7
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Default Re: Why the hole in the top of old 13A plugs?

Or is it to let the magic smoke out

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Old 30th Jan 2019, 1:10 pm   #8
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Default Re: Why the hole in the top of old 13A plugs?

Quote:
Originally Posted by KeithsTV View Post
Or is it to let the magic smoke out

Keith
That is where the cable goes in.
My dad once waggled an intermittent cable on the vacuum cleaner.
When the magic smoke was released it printed an arrow on the wall pointing to where the fault was
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Old 30th Jan 2019, 4:45 pm   #9
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Default Re: Why the hole in the top of old 13A plugs?

The requirement for earthed plugs to have a visible earth wire terminal goes back at least to Board of Trade Regulations of circa 1910, The requirement is mentioned in the GEC catalogue of 1911, although at that date earthed plugs were only offered for industrial use. The earth terminal of the socket, as well as the plug, had to be visible. Possibly this requirement carried over to early domestic earthed sockets. When I was a boy, dad had a box of old electrical stuff which included two circular surface-mounting 3 pin 5A sockets similar in design to the GEC 2 pin sockets of 1911. The earth terminal of one was outside the cover with the clamping screw and terminal bore exposed so that the end of the earth wire being clamped could be seen. The other (possibly later) differed in that the earth terminal was inside the cover. Unfortunately I no longer have either.
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Old 30th Jan 2019, 5:11 pm   #10
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Default Re: Why the hole in the top of old 13A plugs?

They still exist, this one was bought about five years ago.
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Old 30th Jan 2019, 6:18 pm   #11
Graham G3ZVT
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Default Re: Why the hole in the top of old 13A plugs?

When I was a kid, that rectangular hole was a convenient route for the earth wire of my crystal set.
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