On Fri, 19 Jan 2007 09:40:21 +0000, Dave Liquorice wrote:

On Fri, 19 Jan 2007 01:37:17 +0000, Andy Wade wrote:

As someone else said you mustn't rely solely on an earth provided by
the public mains, but there's no reason not to connect your means of
earthing in parallel with a supplier's earth

Except you can't trust the suppliers earth to remain earth under fault
conditions. It could become live with the mains supply behind it.
Remember there are no overload cut outs in the earth (or neutral) wiring
and that wiring is of a hefty size so lots of current, lots of heat, melt
down or *BIG* bang...

Having pondered about use of a generator under mains failure situations
I've decided the a local earth spike to generator chassis, one phase of
the alternator to chassis, RCD on generator output and extension leads to
the appliances is by far the easiest and safest method. One day the CH/HW
system will be fed via a plug top (still on it's own switched fused spur
though) to enable easy transfer to a generator.

When you do that make the socket an unswitched one, then the boiler has an
isolator (as you have to remove the plug to turn it off), and so complies
with the electrical rules.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards