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).

It doesn't look like the earth cable in this example actually goes to
most of the houses. https://goo.gl/maps/QGxRssmS2mkMJuKV8 and https://
goo.gl/maps/YEC7HKgHGvnC1Qy57 shows only two wires over the road to the
house.

The fifth wire terminates here https://goo.gl/maps/DqQoYJcoJCVptT2E7 -
you can see that only four wires continue to the last pole, with the
second from bottom missing.

Where the line branches at Chapel Lane, there are again only four wires,
and there's another four-wire branch just past at https://goo.gl/maps/
DqQoYJcoJCVptT2E7 . And the line ends here https://goo.gl/maps/
zovrrTaZbFnAePZP7 - where you can clearly see that the underground cable
does not connect to the earth wire, only the phases and neutral.

So I think there's a good chance this earth wire is mostly, or even
completely, redundant. It's possible that it's been converted to PME but
the separate earth wire not been removed. .

Mike