On Fri, 18 Jan 2008 14:02:20 -0800 (PST) someone who may be
robgraham wrote this:-

If on the other hand there is an expectation that the fitting should
be earthed, then the OP does have a problem as it is not acceptable to
consider the conduit as a an earth as it will have mechanical joints
in it that may have suffered corrosion over the years The solution
is I'm afraid to pull the two cables back through, pulling in new
cables plus an earth cable.

Pull them back to where? All the way to the consumer unit? That
might be difficult in many conduit systems, as there is unlikely to
be a wire going all the way even if there is space in the conduit.

An alternative is to measure the impedance of the conduit. Despite
the statements of some, conduit can make a perfectly good protective
conductor provided it was installed and maintained properly. A short
flying lead connected to a bolt tapped into the box is then all that
is needed. However, it is vital to measure the PSC at the box and
check that a small copper conductor can cope with this. It may be
necessary to use a larger size than would be standard in a T&E
cable.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54