When houses have their 240V mains supply delivered by overhead wires (eg on wooden poles) in the street, rather than being fed underground to each house, are the three phase wires (and the two wires to each house) insulated, or are they simply prevented from shorting by the spacing of them?
I'm talking about the older wiring where there are three separate wires, rather than the upgraded wiring where there is a twisted bundle of three wires (or four if there is also a neutral). Obviously in the latter case the wires in the bundle will need to be insulated.
I think they're uninsulated. Based on a) their general green verdigris tinge and b) the fact that when building works takes place, the DNO will install temporary sleeving over them.
Some were some not. Its all a bit debatable but I'd have thought the ones into the house were insulated from memory of such a building we rented for a holiday .
Usually not insulated. Even as far as the insulators on the side of the house sometimes (mums bungalow was wired this way). Five wires so presumably N, L1, L2, L3 and street lighting?
Our last house was supplied overhead through fields. 240V from a pole pig several hundred yards away. Originally the wires were uninsulated and about a foot apart. We had to have several poles replaced because of woodpecker damage (yes, really) and I mentioned that the combine harvesters sometimes had trouble getting under the cables, so the power company installed longer poles and two-core insulated cable, in a Siamese configuration (I think it's called - figure of 8 section).
The most impressive thing was the UniMog 6x6 pole handling machine - one guy just "drilled" a hole in the ground and pushed the pole into it. Took about 2 minutes per pole. They just chainsawed the old ones off (and I kept them - one subsequently made a very good gatepost). Despite being over 40 years old, they still smelled of creosote when cut.
I first suspected that they were uninsulated when a lad at school threw a metal coathanger at the overhead wires that ran along the road outside the school. There was a bright flash and the coathanger fell down with a huge nick melted out of the metal. Up until then I'd always assumed that "all" wires were insulated. It was the first time I'd seen overhead 240V cables: all the houses I've lived in apart from the most recent had underground mains.
I wonder how many people would work close to the point where the wires attach to the insulators on the house (eg when painting the house) if they knew that the wires were uninsulated and therefore liable to give you a nasty shock if you touch the live one.
Our last house was one of several terraces each of three houses. All of them were fed from a single feed from the road, with a single multi-core cable stapled all along the back of the house and then a short length of three separate (uninsulated?) wires over the driveway between one terrace and the next. Since there were three wires from the road, I presume different houses were fed from different phases, rather than all of them from the same phase.
Back in the days when creosote was *real* creosote before the H&S brigade "watered it down". I'm not sure what the modern replacement is for creosote, when treating wood to make it non-rotting.
I watched the electricity company replacing the wooden poles and 11 kV to
240V pole-mounted transformer opposite our house. The old transformer was mounted on a single pole, but they replaced it with a new, smaller on, though mounted on two poles a foot apart. The power was only off for about half an hour, so they worked quickly. I always wondered how often they used those pole-mounted switches, operated with the sort of rod that is used to open high windows in a school hall. I imagine that was a prime example: to be able to isolate the 11 kV feed somewhere upstream while they replaced the transformer.
Now I bet if you threw a coathanger at the 11 kV wires that cross the field, you'd get more than a little flash. Mind you, I'm sure the wires are spaced a bit more widely than the length of a coathanger.
Not totally a given - the trips on 11kV (I was told by my dad with was an LEB engineer) wer eusually more sensitive than low voltage, the latter being set to try to blow a fault clear rather than trip if possible.
You should, of course, contact the supplier and have the wires sleeved before working near them. IME it takes them about four weeks to get around to doing it. However, as they don't bother to take it away afterwards, the wires to my house now have yellow sleeves around them
They do take them away eventually. After a couple of months I called to ask and they said they don't come out specifically to remove them, they just do them as and when they happen to be in the area and have time. It was about 6 months, IIRC.
Or field... our supply from pole to house was two wires spaced about
6" apart vertically. The top, live, was insulated, the bottom, combined neutral/earth wasn't. This has since been replaced with a length of 35 mm^2 coaxial which is inulated.
More likely earth. Can't see why you'd need a seperate street lighting supply, each lamp has it's own timeswitch or more likely photocell to turn 'em on/off. At least for ordinary streets, major roads and motoroways have switched circuits.
Some rural places may never have been insulated others did have insulation but all that remains now are a few remnants here and there.
Typically in that configuration the 240v mains on vertical layout starts out insulated but after a while the elements and UV take its toll. Then strips of old insulation come free and swing about in the breeze. In a good storm we used to get lots of arcing and sparking as adjacent wires were shorted together with wet slightly carbonised "insulation".
The failing cables were eventually replaced with a single steel cored tri-phase aluminium conductor which is very insulated and amazingly can almost support the weight of a tree across it.
The poles failed before the cable did.
HT horizontal configuration and EHT is not usually not insulated.
They start out insulated but after a while all bets are off. They will still work OK without insulation unless you happen to touch one.
Three phase wires running horizontally, with two wires from two of the three phase wires going to our house. Ignore the phone wires lower down the pole.
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