On Monday, 28 May 2018 00:18:33 UTC+1, Johnny B Good wrote:
On Sun, 27 May 2018 05:55:32 -0700, tabbypurr wrote:
On Sunday, 27 May 2018 13:07:31 UTC+1, Roger Hayter wrote:

I brief thought experiment involving connecting a generator frame and
neutral output to an earthing stake (about 100ohm if lucky) and then
opening the main service isolating switch to the house and connecting
the house electrics to the generator leads to the possibility, with an
external neutral fault in the supply system, the generator live being
up to 750 peak wrt real earth. Is this a danger that should be
prevented, and if so, how? It would seem to involve isolating the
house protective earth from the utility supply while the generator was
connected?

The point of multi-point earthing is to stop the house earth connection
going live. It does happen, but the risk is low and accepted.

240v rms is 330v pk so 660v pk on the live in the most exceptional
circumstances. Not much of a risk, and dwarfed by what else would be
going on.


If you must assume a worst case scenario,

I don't

let's at least get the basic
calculations right. :-)

I did. The problem with your worst case calc is it's based on a string of highly improbably events all occurring at once. So improbable that I wonder if it's ever occurred in the UK. Which makes it fairly immaterial.


NT