Andrew Gabriel wrote:

I suspect capacitive coupling to a buried cable would do it.
With the plaster all wet and conductive, the capacitance to
something like a light switch drop with both wires live would
be higher than normal.

That was one of my thoughts... although I am not aware of any cables
there (above a window, opposite side of the room from the door). Also
that area of plaster had been hacked back to brickwork and lath without
revealing anything. There is a possibility that there is something
routed above it in the loft - but again that seems less likely since it
is right over to the side of the house away from any lights etc.

I ran a metal detector over the wall and could not find evidence of any
buried metalwork (some parts of the house still have buried pipes from
the old gas lighting!

There is a wall mounted electric radiant heater about 7 foot away that
gets power from a cable drop from the loft though. So that may warrant
further investigation.

However, you should check this out thoroughly, remembering the
death of the MP's daughter just recently after people had noticed
something similar with a metal cutlery rack, which was in fact
live.

Yes point noted! I want to get to the bottom of what was going on
anyway, if even just out of curiosity.

--
Cheers,

John.

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