On Sun, 21 Sep 2008 15:03:16 -0700, jim wrote:

would earthing the existing metal conduit and thus not needing RCDs be
a goer? Or have I missed something....

I think you'd have to guarantee that the conduit formed a good earth for
its entire length so that when muggins blasts through it with his electric
drill and contacts the live conductor it passes enough current to earth to
operate the circuit protective device (fuse/MCB/whatever). Unless the
conduit is substantial screwed steel that's unlikely to be the case: most
conduit I've seen in domestic installations is rolled thin metal
sheet joined with similarly flimsy clamps at junctions, none of it
guranteed to give a good circuit.

--
John Stumbles

Fundamentalist agnostic