Things that can & cannot touch PVC cable insulation?

[Adam Funk]

It's well established that polystyrene (thermal insulation, for example) isn't supposed to touch PVC cable. But I was surprised to be advised here a while ago by someone reliable that it's OK to put gloss paint on it (I'd always assumed the solvent would be bad for the insulation). And it's nice to know that Sharpies are OK.

Is there a definitive list of things (within reason, that is, particularly things like types of thermal insulation that you might put there without realizing it) that aren't supposed to touch PVC cable? Are there any other surprising things that can touch it?

[dennis]

Polystyrene isn't much of a problem. It reacts with the plasticiser to make the PVC less flexible but the plasticiser causes the polystyrene to shrink. Once its shrunk enough to create a gap the problem has gone away.

[Tim Watts]

Not aware of any. Sharpies do have a solvent in, but mostly leave pigment behind which is harmless.

You would maybe consider gloss paint to be a danger item, but people have been painting (and varnishing) cables forever without obvious issue.

Polystyrene is a rather non obvious and fairly special case. Perhaps might never have been noticed except for cavity wall insulation.

[Tim Watts]

Except if the polystyrene is in the form of loose beads in which case it may just move down onto the cable.

But as you say, if the cable is not subject to movement, you might never find out its a problem... Not that you should ever knowingly do it of course!

[Andrew Gabriel]

Oil based gloss paint will dissolve into the surface and carry the paint pigment in, but it doesn't go far enough in to do any harm. Because the paint pigment is dissolved into the PVC surface, it won't ever flake off. You use top coat only (no undercoat is needed because top coat binds directly).

(Same is true for gloss paint on PVC window frames, PVC waste pipes, etc.)

I have not tried this using the current low volatiles gloss.

I did come across some T&E cable clips made from polystyrene. Each one looked like it had slightly melted onto the cable, and at a first glance, I thought the cable might have melted at some stage, but it hadn't.

I don't know of any list, and neither the paint nor the cable manufacturers will tell you it's safe to paint the cable with gloss paint. Dried gloss paint is more flammable than PVC, so there may be some situations where it's not advisable.

[Bill Wright]

But often the cable is loose on top of the polystyrene, so as the latter shrinks the cable moves downwards and keeps in contact.

Bill

[Brian Gaff]

I think with paint it depends on the base of the paint, but one issue is that it never seems to dry well on pvc, it goes tacky.

Make sure it does not get too hot of course, and from experience hot and cold cycling or exposure to sun for long periods does not do it much good either, though I guess it depends on the quality, something you have to take on trust. Brian

[dennis]

Eventually it will go through and find somewhere polystyrene free to rest or hang. Maybe someone can get a polystyrene tile and some PVC cable and setup a webcam. It would be better than the watching paint dry ones.

[Mike Clarke]

While agreeing that PVC cables and polystyrene should be kept apart I don't think the potential risk is very high.

Recent work in my house revealed that we had 2 inches of polystyrene behind the plasterboard in most of our rooms. PVC cables were run behind the polystyrene without any protection and did show some sign of hardening on the surface but not enough to cause any problem. The cables and polystyrene have been there for at least 10 years, possibly nearer 20.

I certainly don't feel any need to replace all the existing cables though I did make sure that the additional cable I installed for the extra sockets was well separated from any polystyrene.

[Matthias Czech]

Am 18.11.2014 um 10:47 schrieb Dennis@home [The slow movement of a PVC cable on polystyrene]

For the guys with a little patience:

Background:

Have a beer, relax and watch!

[ChrisK]

As an example, just unpacked the old BBC micro to pass it on, it has been sitting in its original PS foam packaging for 15(?) years or so at normal room temperature. Where the PVC mains lead was pressed up against the foam polystyrene packaging it has gone all sticky. It seems that the platicisers leaching out of the PVC had turned the PS into a sticky goo a bit like printers' snot but could be peeled off the cable leaving it more or less unmarked.

Chris K

[Johny B Good]

I rather doubt that. Watching paint peel, otoh, might be a more comparable pass time.

[ARW]

Apprentices.

[Adam Funk]

I thought you *made* them hold the ends for the insulation testing --- oh wait, it's not the insulation that they touch...

[Adam Funk]

Interesting, thanks (& to Tim W & others).