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What is the purpose of the gap on the live pin of this plug?

I've never seen this before and was why this gap was their since the plug is only for an alarm clock.

The gap goes down the middle of the live pin to half way down the pin the pictures below show the plug.

enter image description here

enter image description here

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    \$\begingroup\$ Probably purely mechanical reasons, since the top forms one end of the fuse holder and needs a certain degree of 'springiness'. \$\endgroup\$ – brhans Aug 2 '16 at 0:31
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    \$\begingroup\$ That's a very old plug, and could no longer be legally sold. There should be insulation around the first 8-10mm of the pins, so that if tiny fingers get in there before the connection breaks ... you get the picture. \$\endgroup\$ – Brian Drummond Aug 2 '16 at 10:06
  • \$\begingroup\$ The clock has chips dated 1980 on it and because you had to wire plugs yourself back then the plug itself probably predates that which would explain the lack of insulation. I just found it to be very odd as I've never seen a design like that before, thanks everyone for your answers :) \$\endgroup\$ – bob1252 Aug 2 '16 at 20:49
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The live pin has a gap because the part on the other side of the plastic forms the fuse clip. The gap will have no affect on the current-carrying capacity of the pin, but the two parts on either side of the gap form the fuse clip as your photo shows very nicely. Clever design.

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As you probablly know british BS1363 plugs have a fuse, normally one of the fuse clips is on top of the live pin, while the other is attatched to the live terminal.

On most plugs the fuse clips are made out of peices of springy sheet metal rivited to the pin and the terminal. In this case though it seems the manufacturer has machined the fuse clip and the pin out of a single peice of metal.

But the fuse-holder needs to be springy enough to allow the fuse to be inserted and grip the fuse once it is. Presumablly they couldn't acheive the right level of springyness by machining the top alone, so they cut a slot which acts as a lever and allows the fuse to be inserted without requiring excessive force and without bending the metal beyond it's elastic limit.

The other fuse clip seems to be of a more conventional design.

This plug is clearly old, pin insulation was introduced to the BS1363 standard in the 1984 revision, though i'm not sure when it became mandatory for plugs to follow the new revision. I suspect it would be difficult to implement pin insulation on a plug with such a slot.

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