Lars wrote:
My electrical theory is fair but not great. Can someone please
advise me.

I have an old Anglepoise lamp with painted metal arms and painted
metal lampshade (Anglepoise model 90). It has a two-core mains
lead. I am in the UK so this is all at 230-240 volts.

Today I touched the outside of the lampshade and got a sort of vey
mild tingle feeling which felt "odd". When I used a mains tester
screwdriver on the exposed metal (at the joint of the lampshade
and support arm) then it glowed as if the metal of the Anglepoise
lamp was live.

I unplugged the lamp and tested the resistence between the live
pin on the mains plug and some exposed metal on the lamp. I got
no resistence reading at all (i.e. it must have been a very high
resistence). I then tested the neutral pin in the same way and
got the same high resistence result.

So the lamp seems ok. But something seems to be wrong!

QUESTION: Is my lamp safe to use and could I get a shock from it
in its present condition?

QUESTION: If my lamp is unsafe then is there a repair I can do?

It's probably just capacitive leakage between the live wire and the
metal, and is unlikely to be serious, but what is serious is that the
metal isn't earthed. The resistance measurements aren't completely
reliable, as presumably they were made with a low-voltage source rather
than a few hundred volts, but they do suggest there isn't a direct short
of wire to metal.

You shouldn't have any appliance with exposed metal parts which are not
earthed. Such an appliance needs three-core cable and all of the metal
parts well earthed. In an anglepoise, in particular, there will be mains
wires flexing every time the lamp is moved. Eventually the insulation
will crack, and a wire will touch the metal body. You really want a good
earth at this point.

I would recommend fitting a three-core cable, making sure the plug fuse
is correct (almost certainly three amps) rather than the default 13 amp
one that came with the plug. Again, particularly with an anglepoise, it
would not be safe to assume that all the metalwork is in good electrical
contact and that earthing at the cable entry point would provide a good
connection at the shade.

For maximum safety, I would replace the existing internal wiring. If
it's really old, then it may have deteriorated significantly,
particularly in the hot area. Probably any paint at the lamp joints will
have worn away long since, but I'd consider using star washers on the
joints and linking around the 'elbows' of the lamp with wires to solder
tags screwed down over the washers. That way, the shade, the part most
likely to be touched, should have good earth continuity.

Maybe you can go on using it as it is for decades more without incident.
Are you feeling lucky...?