In article ,
Me wrote:
But in my house, re-wired in 1982, all the cables in the walls are less
than 50mm deep and in plastic oval conduit

I don't think plastic conduit would offer any protection from nails -
especially fine sharp ones like for picture hanging.

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*Gaffer tape - The Force, light and dark sides - holds the universe together*

Dave Plowman London SW 12
RIP Acorn