"Tom B" wrote in message
...
On Sat, 24 Jul 2004 12:33:03 +0100, "Farmer Giles" wrote:


"Tom B" wrote in message
.. .
On Fri, 23 Jul 2004 21:24:13 +0100, Lurch

wrote:

On Fri, 23 Jul 2004 17:56:18 +0000 (UTC), Tom B
strung together this:

Errrr... I must be missing something here. What is the point of
connecting all
the bits of metal together but not to earth? This doesn't "make
everything in
the bathroom at the same voltage". It just makes them all
'floating',
just the
same as if you leave them individually 'floating'.

By cross-bonding everything you are holding them all at the *same *
floating potential. If you don't cross-bond them then they are at
*different* floating potentials.
How come?

If they are floating there is no source (or sink) of current to do any
damage.


Current source and current sink are two entirely different things - and
have
nothing to do with the subject under discussion.

Errr... best stick to the farming :-)

Actually I am a graduate electrical engineer with over 30 years experience -
it is you who clearly do not know what you are talkinf about.




Let me try one last time to explain my point:

Voltage on its own is not dangerous - think of birds sitting on the 22kV
power
line. Wearing suitably insulated shoes, and with one hand in your
pocket, you
can touch a live point without getting a lethal shock .
If you then with the other hand touch a piece of metal that is not
electrically
connected to anything else ('floating') then again you are still quite
safe. (Ok
you pedants out there, there may be a very small leakage current, I'm
trying to
keep this simple).

However, if you now earth the piece of metal and repeat the exercise you
are
very likely to die. (Assume no RCDs here, only 30A fuses)

You can not of course get a lethal shock by touching two separate isolated
pieces of metal. The key word here is 'isolated'.

In other words in some circumstances it can be more dangerous to bond
than
not. . I think others were making the same point.

The point you are making is about potential difference. The point you
introduced about source and sink current has nothing to do with it. If all
metalwork is cross-bonded then you create an equipotential zone and no PD
can occur - and therefore no current can flow.