On 17/04/2021 00:06, NY wrote:
On 16/04/2021 23:02, Mike Humphrey wrote:
On Fri, 16 Apr 2021 18:46:38 +0100, NY wrote:
What are the circumstances when overhead mains wiring has an extra earth
wire, rather than the earthing being done at each house? I've never seen
it before. Come to think of it, why do some installations have a neutral
wire and some don't - are there cases where the nett load is expected to
be unbalanced on the three phases, requiring an extra neutral?

A neutral is required - the houses will have a single phase supply, so
will connect to one phase and neutral. Where you won't see a neutral is
on the HV lines - the neutral is created at the transformer.
A separate earth cable on overhead cabling is unusual - most often it's
PME (so combined N/E) or TT (an earth rod at the house).

Are you saying that overhead mains wiring is *always* 4-wire (or 5-wire
if there's a PE), with every house connected to one phase and neutral?
And not houses connected to two of the phases? I *thought* I'd seen
three wires rather than 4 in some cases. But I may well be
mis-remembering it.

Der!!! I *am* misremembering it. Neutral should be virtually at earth
potential (*), not at one of the phase potentials. Of *course* there has
to be a separate neutral line to make this happen ;-)


(*) I believe in some installations, neutral is actually bonded to earth
at the premises.