In message ,
"BigWallop" wrote:


"wanderer" wrote in message
...
On 7 May 2004 12:27:25 -0700, Lobster wrote:

snipped (quite a bit)

Would be grateful for some clarification!

HTH - I've simplified things quite a bit but the basics are there - the
pedants will be along in a minute to argue about the terminology! :-)


No. You're right. All the basics are in there and you explain it to the best
understanding you can without going into all the techie thingies.



The scary thing about PME is that there is a possible failure mode where
the power is off, but everything is still live, and unearthed. This
would be the case where somehow someone cuts through the supply
company's neutral just before it enters your house, but not the live.

As has been said, the supply company goes to great lengths to earth the
neutral (hence "multiple") as securely as possible to prevent this, and
the use of concentric cable makes it extremely unlikely, but having PME
makes it even more important that main and supplementary bonding is
correctly used.

Actually, come to think of it, there is a possible failure mode in a
TN-S system where the earth disappears but L&N are still live. That
could be quite dangerous too, if a fault develops in your
installation...

Maybe we should all go back to candles :-)

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... I've used Basic so long, my brain has gonesub permanently