*Five* wire overhead mains cables

Now, with an image, there's something to go on.

Looking at the second link, the fourth cable from the top terminates at a house further on to right, and at a pole further to the left. It looks to be thinner, and is not obviously driven from 3-phase drives?

So who knows?

And wouldn't you - even if was only meant for for this or that, use an cable insulator/anti-rubbing item of the same kind as already in use in that area?

PA

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?

With the phone wires on (as far as I could see) the same brown porcelain insulators as the 240 V mains wires?

This is the wiring

Only four wires coming from the pole mounted transformer, the fifth wire just seems to go from pole to pole down the street

TN-S system (not TN-C-S)

L1, L2, L3, N, PE

On 16/04/2021 16:25, NY wrote: ...

The top three are the three phases. The bottom one is neutral and the one between, which, if you look carefully is not insulated, is earth.

It was a common arrangement in some areas.

In the Uk you can't mix mains and telephone. % wire 3 pases, neutral & earth.

See photo here (it's not good, and you'll have to zoom in a bit)

A temporary 500kW generator was required recently to cover for some work on a nearby substation. It was connected up to the overhead lines nearby. There were five cables from the generator to the lines. The upper three were connected to, I expect, the three live phases (they are the upper three cables with the yellow insulated connectors). There were two further connectors (uninsulated?). They are the lower two in the photo, and both appear to be connected to the fourth line( below the three live phases), which I assume is the neutral. Would those two connections be neutral and earth from the generator to make a common neutral/earth connection?

Depends what you mean by mix. Both around here - and in NY's links - you can see telephone lines sharing the poles.

There'll always be some imbalance. Different loads, and not every third house on the same phase.

They do, but in both wires - so that's ok (theoretically)

PA

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?

I thought they picked up hum if they ran parallel to an electricity cable.

We have an extra cable, not insulated around here which is a low voltage data signal carrier.

How come I am having problems in my flat where my final extension has a hum and the cable runs very close to the electric ring main. The other extensions do not have this issue.

The setup shown is typical of pre-war rural area electricity distribution systems, which are as I describe.

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.

P1, P2, P3, N, E

It is an optical illusion the phone line is below the mains wiring (and in prehistory the mains was probably insulated but not any more). Ours failed by having strips of the rubber insulation fall off and short adjacent phases in bad wet weather with much arcing and sparking.

The phone line goes from low position on an electric pole to a higher phone pole set back from the electricity lines so there is no danger of them rubbing together. Phone is below mains wiring on our poles.

My own village was wired about like this until the insulation fallign off kept bring the entire network down. It was replaced by three core aluminium conductors platted around a steel hawser down the middle.

The new wiring proved strong enough to resist a tree falling across it although the supporting poles ended up like bananas and one side of the street was disconnected from supply. I have a picture of it somewhere. My hedge has still not quite recovered from the damage.

The poles now have little plaques on "unsafe: do not climb".

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.

The fifth wire terminates here

Where the line branches at Chapel Lane, there are again only four wires, and there's another four-wire branch just past at

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

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.