On Wed, 24 Sep 2008 07:41:31 -0700, mark.hannah wrote:

I would have thought that there was still enough metal-to-metal
contact in a compression joint to maitain continuity?

Yes, if they're done properly with PTFE over the olive rather than on the
thread of the fitting which the nut screws onto (where it is absolutely
useless since this threaded joint does not provide the seal, only
mechanical compression).

Actually neither PTFE nor any other jointing material should be necessary
on compression joints, made with unblemished pipe and new fittings in
clean conditions: it's when one's obliged to re-make joints that
something's often helpful to get it to seal, and here a couple of turns of
tape round the olive or a smidgeon of Boss White/Green/Universal
(according to application) can be used.

--
YAPH http://yaph.co.uk

Things don't like being anthropomorphised.