Overhead power lines

[Steve Loft]

Are overhead power lines - the ones that bring the mains to the house - usually insulated in the UK?

[ChrisM]

If you have overhead power lines actually into your house (I thought they were always underground...) then I would imagine they would be. If you are talking about pylons, then no..

ChrisM.

[Jonathan Pearson]

In rural areas, overhead lines are common, usually the last leg from the pole to your house is insulated, but anywhere else they are not. Jon

[Ian Stirling]

If there are multiple cables, then no. If there is one, then yes, otherwise it glows bright orange, and doesn't deliver much power.

[wanderer]

Depends if they're old or modern.

If you have two wires from pole to house then one will probably be insulated - the phase, and one bare - the neutral. The lead-in cables from the eaves to the meter position will be insulated.

Very old services will be insulated with PBJ - poly butyl jute. This tends to deteriorate, harden and crack, particularly where it bends and twists, like the eaves. Modern services will be 'pvc' insulated.

A considerable number of services have been replaced with a concentric aerial cable - if you only have one cable from pole to house this may be what you have, although some RECs also use twisted aerial cables.

If the cables appear to have a reddish brown woven fabric outer coating be very careful - that is PBJ and could be quite dangerous to work close to that.

HTH

[Grunff]

Everything down to 11kV isn't insulated. Once you're down to 400V/230V drop wires, it is.

[Steve Loft]

I've had the binoculars out for a closer look. There are three wires going from pole to pole. They all look to me like they're bare - I can see green twisted wires.

The top and bottom wires have connections to the house. The top connection to the house appears to have black insulation on it, the bottom one is bare. The bottom wire also has a connection to it (at the pole) which goes down the side of the pole and disappears underground. So I assume the top one is phase and the bottom one is neutral. So what's the middle one?

I have two reasons for asking about this. First, the cables enter the house just above the flat roof over the 'veranda'. At some point I will need to get up there to paint the house and renew the flat roof. I wondered how careful I needed to be with regards the wires.

Second, this morning one of our cats shot up the pole (it's one of two in our garden) all the way to the top. She struggled a bit when she decided to come down, and it appeared that at one point she was touching both of the top wires, and now that I see that the wires appear to be bare, I wonder how she got away with it. I guess the answer to this depends on what the middle wire is actually used for.

[wanderer]

Probably copper mains, with a coating of copper oxide. Insulation on lv imains is usually black. Green pvc is used for hv, unless some was put up in an emergency at some time or other.....

That's the phase conductor, sounds like it's fairly modern, with pvc insulation.

That's the neutral

The bottom wire also has a connection to it (at the

PME electrode almost certainly......

Probably another phase conductor, just that it's not used for your supply. Might be a street lighting switch wire, but they are usually at the very top.

Treat them with respect, you should probably be ok with painting, as long as you always remember they're there! As to re-roofing, most leccy companies used to fit a temporary 'working' insualtion over the wires, that they never get round to removing after the event - dunno what part of the country you are, but chances are that you can drive around most villages with o/h systems and see odd lengths of a thick and stiff-looking yellow plastic that's been put up where people are working in proximity to low voltage overhead systems - they used to make a charge for this! The alternative is to ask for a new concentric aerial service if your REC does these, but again there'll be a charge.....

Hmm, sounds like she used up one of her lives this morning........

[The Natural Philosopher]

No. Or yes.

If they are separate L & N, then usually unisnulated. If a big fat bundle together, they are insulated.

The latter is more modern.

[Lurch]

On Fri, 16 Jul 2004 13:01:47 +0100, Steve Loft strung together this:

If you get in contact with whoevers cables they are they will usually pop round and slide some plastic sleeves over the wires near to the house for you, you've probably seen those 2"ish diameter 15' long yellow sleeves dotted around somewhere on the sides of houses.

[Andrew Gabriel]

Yes -- sounds like a PME/TN-C-S supply.

A different phase -- look to see if it feeds another house. If it's thinner, it might be a switched supply for street lighting.

I've seen sleeves placed over the wires during decoration, usually bright yellow. I don't know if you have to pay for this service.

Dry fur is a good insulator, but still wouldn't recommend putting it to the test!

[wanderer]

Didn't do the ginger tom much good when he got across the bushings of a

33kv OCB......

Funnily enough, the cat was still more or less intact - not badly burned or unrecognisable, just very dead.

[G&M]

The line is placed inside a twisted sleeve connected to neutral. This often forms the earth for your system as well unless you change it.

So it isn't really insulated but is safe.

That said, if you have on the the two prong insulators on the side of your house where the overhead line attaches, one bit is both live and exposed. Do not work near it on the roof without covering it in case you fall on it.

[Steve Loft]

Ah, now that's interesting. I'd been trying to work out where our earth is, since we have an overhead supply. And, having looked up TN-C-S in the FAQ, it seems that's what we do have. I hadn't previously noticed that there's an earth wire going into the top of the main switch, presumably to connect to neutral.