When a power pole falls down

[Matty F]

and the power for the whole neighbourhood goes out and you walk along the road to put road cones to warn drivers not to hit the pole and wires, you need to have a good torch. Why are powerlines black?

[harryagain]

It is the colour least effected by sunlight as regards the plastic insulation. ie It prevents the light from penetrating into the plastic.

[polygonum]

Evidence?

My expectation is that by reflecting the light better, white might be best.

Anyway, whatever the colour of the bulk of the insulation, regular stripes of 3M reflective material (or something similar) might be sensible wherever a line runs over accessible ground.

I note that much of the cabling withing the London underground is a sort of mauve colour. Even when overground.

[Broadback]

Ours are quite a bright green.

[Thomas Prufer]

Uv protection, probably.

UV-resistant cable ties are always black, as far as I have seen (well, the plastic ones, ok?). The white/translucent ones go brittle outside eventually. (Takes a few years here, but my here and yours probably differ there...)

Thomas Prufer

[Artic]

Matty F scribbled...

Cost

[Tim Streater]

Eh? If it's black, it's *absorbing* the light falling on it.

[polygonum]

But it is the dye/pigment added to the polymer that is absorbing the light. It *might* be that protects the polymer itself even if it heats up more. But without evidence, who knows?

[Brian Gaff]

cos they are dirty after being up in the air for years? Might have been a natty shade of yellow when put up. Brian

[John Williamson]

The damaging ultraviolet is all being absorbed by the first few microns of the black pigment, generating heat, and can penetrate no further. If the wire is white or the insulation is just its natural colour, the UV can penetrate much further into the insulation, causing damage faster than happens on a black cable.

While it might be possible to mke other colour dyes that absorb UV totally, they'd be more expensive than the black one currently used.

[Dave Liquorice]

Not sure were the others get the idea that 11 kV local distribution wires are insulated. They aren't, at least in the UK. They are just bare copper about 3/8" dia, well oxidised to dark brown... New lines are nice and shiny but they don't stay that way long.

[Bob Minchin]

Ours were bare metal until a few years back. Caused a nice firework display in freak winds when they would occasionally touch and leave solder like splashes on cars parked nearby (Aluminium & steel cables)

Now they are 3 coaxial cables twisted together and obviously insulated in black.

[tony sayer]

Its Carbon Black which stops the plastic deteriorating in UV light.

We've got some stuff on a Broadcast site that was installed with clear Tie wraps and after a few years they have all fallen off and have now broken and its costing us a packet to have them replaced by the correct Black ones which don't got the same way;!...

[The Natural Philosopher]

+1

[Fredxx]

Absorbing light (and UV) is the cause of the destruction of the plastic. Much better to reflect it with a white pigment, such that absorption is minimised.

Temperature also has a significant on the ageing of plastics, all the more reason to be white to reflect all that visible energy.

[harryagain]

But the black pigment best prevents the light from penetrating beyond the surface. And it makes the cable more unobstrusive..

[harryagain]

The phase side of overhead LV cables is insulated round here (black), neutral is uninsulated.

[polygonum]

Gets pretty damned obtrusive if you walk into it in the dark.

"Best"? I'd hazard a guess that the best might be a wrap of aluminium foil.

[Tim+]

And that'll be why you see so many white power cables.....

Tim

[Nick]

Why do touareg and other berber folk choose to wear dark clothing in very hot climes?