wrote:

On Sunday, 27 May 2018 15:23:21 UTC+1, ARW wrote:
On 27/05/2018 13:07, 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?


If you have an external neutral loss on a PME them you have also lost
the earth.

With a local genny you add a local earth rod, so it's not that simple.


NT

So in theory, especially if you have a fairly low impedance earth, then
someone else's neutral return current can be trying to flow down it.
In our case, sharing a pole transformer with 4 houses with overhead
supply, there won't be that many (if any) multiple earths apart from the
one at the transformer pole and mine. In theory the neutral for all of
us could separate from both transformer and earth near this pole,
leaving the neutral side of the transformer secondary earthed.


--

Roger Hayter