On Tue, 24 Nov 2009 11:10:26 +1100, Sylvia Else wrote:

the net result would be a
large overvoltage on one set of appliances.

It would be across both sets, but......

My electrician says it's not an issue, but I can't see why.

The neutral is actually grounded to the earth for such a case; hence MEN
(Multiple Earth Neutral), so the neutral would actually travel through
the ground to your neighbours earth stake and back into the neutral phase
there.

If the USA Godzilla remake is to be believed, all your earth worms will
come to the surface as an indicator, (or is that only for correct DC
connections?).

If you are worried about such an event happening, dump a bucket of wter
on your earth stake quarterly and encourage your neighbours to do the
same.