"Harry Bloomfield"; "Esq." wrote in message
...
When did building regs (or normal electrician practice) change from using
metal to using plastic conduits? I can imagine metal conduits would block
any volt stick, especially if the conduit was earthed.

Why would you expect them to work through metal or screening? Either metal
or plastic conduits are in use.

As I said above, I *wouldn't* expect them to work through metal conduits. I
presume that was one of the reasons (along with cost, weight and ease of
cutting) for conduits mostly being plastic nowadays. Though maybe *good*
conduit tracers can detect either induced voltage from live wires, for wires
in plastic conduits, or can detect the alteration of a magnetic field (metal
detector principle) for metal conduits, irrespective of whether there's a
current flowing. Usually, the ability to trace where buried wires go is more
important than to detect which wires are live - usually it's for working out
where it's safe to drill or nail into a wall when putting up a picture etc.

I'm not sure how the batteries in my B&Q detector last as long as they do,
because there's no on/off switch: it's permanently on and just bleeps (but
very unreliably) when you put the tip near a current-carrying wire.