On Mon, 05 Apr 2004 10:57:50 GMT, Lurch wrote:

That would also apply to anything plugged directly into the genny.
It'd be no more 'unsafe' than just plugging something in to an
extension lead on the genny.

Not quite, a single appliance on a extension with a L E fault will
only mean that that appliances N and/or E rise above true E. In an
installation the *whole* installations N and/or E rises. In the case
of E rising all the back boxes and fitting screws of the sockets etc
or exposed earthed metal work on any connected appliance or E bonded
fittings (CH pipe work, taps etc) all becomes a shock hazard...

A raised N shouldn't be so much of hazard but could still present a
"surprise".

Also as N and E are quite likely to be interconnected somewhere the
installations E could also rise to the full generator output
voltage.

Where would they be connected?

I hedged that statement a bit. B-) With proper DP break before make
change over switch there shouldn't be a N E connection, other than the
one intended at the generator.

One end of the generators winding needs to be bonded to the frame
of the generator and to local earth and to the main earth terminal
of the installation. It is the bonding of local earth to the main
earth terminal and thus the suppliers earth that can be
problematical with some types of installation.

That is why when using a gennerator you should isolate the suppliers
earthing facility with a link, or just unscrew it, and turn opff the
main switch of the CU or use a changeover switch.

Personally I'd get the type of supply changed such that the suppliers
earth can remain connected or fit a 3P switch. Having to to a manual
disconnect/connect the earth is just asking for it to be left in the
wrong state at some point.

Assuming that the gennys earth terminal also bonds to one of the
generators phases.

I seem to think that most are.

"think"! I'd make damn sure it was, no assumptions or "thinking".

--
Cheers
Dave. pam is missing e-mail