Moulded mains plug failure

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Hi, I've got a vintage Scope soldering iron, direct 240V connection (no
transformer, the cord goes straight into the iron). It dates from early
80s IIRC, and has given faithful service over all this time. No model
number marked so I can't provide it here, it has a red handle. Recently
it stopped working, to my surprise the problem was at the plug end of the
cord, not the iron end. The element resistance is fine, and the element
to shaft resistance is off the scale (haven't meggered it).

The mains plug is moulded and sealed. For all 3 leads including earth,
the resistance from the plug pin to the associated lead is erratic,
varying from many K to many megs. Might there be some sort of protective
device built into the plug, such as fusing? Strange though that the earth
wire continuity has gone. All in all it sounds like a straight age
failure, just wonder if there's something else there that I should be
aware of. Any suggestions on possibilities? TIA

Re: Moulded mains plug failure
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The wires have broken, a fairly common problem on moulded plugs.

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If you are really interested perform surgery and cut the rubber off with
a stout knife and investigate if there is something strange tell us

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That's a common problem, the wires have simply broken through fatigue,
there is almost certainly no protection device in the plug. Just
replace the plug.
But personally I wouldn't bother, bin it and get a proper temperature
controlled station.

Dave.

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...and AFAIK, you should NEVER, under any conditions, have less than close
to zero ohms continuity between an earth pin and the frame of an
appliance...



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But you should get less than one ohm if you measure between the earth
and neutral in a GPO socket.

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Eh ? What has that got to do with the price of fish ?

Graham



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I think the point he was getting at was the the earth could fail first, and
you'd be blissfully unaware of it until the fatal shock.

Hence ELCBs / RCCDs should be mandatory in ALL installations.

Graham


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For him, it might have sentimental value.
I have a Portable CTV (Akai) purchased in 1995. Works like brand new.
I would'nt part with it.

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In the early days, it was common to cut off ANY moulded plug (from
new) and replace it with a standard
aftermarket plug, there were that many failures.  One I remember was a
70's vintage Hanimex fluorescent desk lamp where moving the cord
around near the plug caused the light to go on and off.

Other problems with moulded plugs from that era is the cord outer
sheath coming free from where its attatched to the entrance to the
plug, exposing the coloured wires inside. While the plug will still
work, its not very safe.

The few moulded plugs I managed to hack apart years ago typically used
spot welding or direct crimping to the pin to make the electrical
connection. Obviously it isn't good enough in some cases.



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I bought an inexpensive but decent looking 4 way extension lead from a local
supermarket some years ago.

It didn't 'feel right'. I examined it and no, it wasn't welded but used
standard screw down connections made by cheap Chinese workers.

The thing that 'didn't feel right' was a single strand of copper wire attached
to the live connection of one of the outlets that had 'missed the hole'. I
corrected it.

Heads you lose, tails you lose.

Graham



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   As opposed to shoddy British labor?


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Re: Moulded mains plug failure
On Mon, 29 Dec 2008 07:23:48 -0600, bruce varley

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AFAIK British mains plugs (not the moulded type) protect the active
wire with a user replaceable fuse. I doubt that your plug is anything
out of the ordinary.

I've had to replace the mains cable on my old Micron temperature
controlled soldering station twice, but then I'm in the habit of
packing my iron away after each use. Both times the break was at the
iron end. BTW, I've since dropped the hand-piece and fractured the
ceramic element inside, so if anyone needs the unit (cat # T2441, 60W)
for spares, they are welcome to it.

- Franc Zabkar
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Please remove one 'i' from my address when replying by email.

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The moulded type also have fuses inserted from the 'bottom face'.
http://en.wikipedia.org/wiki/File:Bs1363-plug.jpg

However I did once find ONE with no visible fuse. Maybe it was internal and
'one-shot' ?

It's great to have the safest electrical system in the world !

Graham


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   The safest system is the one that was never built.



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Re: Moulded mains plug failure



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I'm sure you could contribute very positively to that.

Graham


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   Certainly.  Anyone could. by following any of your rejected designs.


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Re: Moulded mains plug failure



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NO design of mine has EVER been rejected. In fact I've turned design
failures into commercial successes.

Don't believe me ? I'll get a PhD to send you an email.

Graham


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  Great, you know a 'pointy headed dunce'.  I'll bet he has a 154 IQ,
too?


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Re: Moulded mains plug failure



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Have worked with.


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One of the most able engineer-directors I've ever met.


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Probably more actually.

Graham


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