"Stefek Zaba" wrote in message
...
BigWallop wrote:

No it doesn't. Neutral and earth points are taken from the place at
earth
mass, so how can a short across neutral and earth cause an imbalance
between
them, when they are already short circuited together at the point where
they're both connected to earth mass. It can only happen when one of
the
conductors of either earth or neutral has risen or dropped below the
potential at which they where both connected to earth.


Sigh. My last word follows, you're welcome to have the real last word.

If you persist in the mistaken belief that 'neutral and earth points'
are in all non-fault situations already 'shorted together' at zero
resistance, I'm sure there's nothing I can say which will shake your
belief. The fact that the belief is wrong, will mislead you in doing
fault-finding on RCD trips (and propagating the belief would mislead
others), doesn't take into account the finite resistance of copper
conductors, and that in the case of current-balance RCDs the *location*
of any such 'final' bonding of N to E is crucial in understanding how
the current flow divides up between a through-the-RCD path and an
around-the-RCD path - all of that is is just sad; at least until such
time as parts of that belief affect the safety of others.

I don't doubt that the bulk, and quite possibly all, of the work you do
both personally and professionally in the electrical sphere is both safe
and competent. If part of your mental model about how it all works is
interestingly non-standard, it doesn't matter that much. Hell, one could
go through an entire career in electrical installation and design work
believing that current was carried by little green worms (which don't
like wriggling through narrow wires), or indeed that it was the mass
movement of electrons themselves, without doing anything dangerous...

Stefek


Please begin reading he http://www.tlc-direct.co.uk/Book/5.1.1.htm and
continue through the menu list until you reach the end. Maybe then some of
what I've been trying to explain will become clearer.

Thanks for the discussion on this though, it has made me mentally revise
many of my very early lessons from many, many years ago. :-)