"Scott" wrote in message
...
On Fri, 16 Apr 2021 20:36:02 +0100, charles
wrote:

In article , NY wrote:
"charles" wrote in message
...
In article , Peter Able
wrote:
On 16/04/2021 15:57, NY wrote:
I'm used to seeing three-wire (three phases) overhead mains wiring
from poles along a street. Sometimes you get four-wire (three
phases
plus neutral). Modern wiring is a single larger cable which is the
three (or four) wires twisted together. In each case, two wires
(between two phases, or one phase and neutral) go to each house,
with a different phase for each house or group of houses.

But I'm mystified about five-wire mains. As far as I could see, all
five wires were the same thickness and were each fastened to the
same type of insulator on the wooden poles - so probably not
three-wire mains and telephone.

What would the fifth wire be used for?

Telephones - well it is around here.

PA

In the UK you can't mix mains and telephone. 5 wire 3 phases, neutral
&
earth.

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?

Are you saying that telephone wires in the UK always require separate
poles and can't be carried on electricity poles?

that certainly used to be the safety requirement. Nobody wanted 240v on
their telephone.

I would have thought 240V at the exchange would be an even bigger
problem.

Nope, they have to have some protection against lightning strikes
and that works for 240 volts too. In fact many street power lines
have 11KV lines at the top of the poles too and sometimes someone
drives into a pole and brings it down, with the 11KV lines with it.