Expanding foam and mains cable - safe ?

Small sausage sand bags? Say 6" long 2" wide and inch or so thick. Old sheet stitched and filled with dry sand.

It's not so much the foam attacking the PVC but the thermal insulation properties making things to warm. With sand bags you could possibly space things out a bit, laye or bags, a few spaced cables, another layer of bags, more spaced cables etc. Easy to remove should the need arise.

You are probably thinking of expanded polystyrene such as chips or beans, thay do attack cables and it doesn't take very long. We've had Items returned for repair and the cable has been attacked in less than three weeks.

I wouldn't trust cables and expanding foam together, lest it is even worse long term. or a reaction ocurrs during the wet phase.

Could you pack it with pieces of fibreglass / rockwool mat. ?

DG

I used it to do exactly this job..hold meter box (with draughts) into the walls.

No ill effects 6 years later.

go fer it. Anyone contemplating massive expasnion can add a sub CU anyway.

HI Derek

Thanks for the reply - comments below

That's my worry. It'd be something of a pain to have to re-do the last 6" of every mains cable !

Possibly. The CU's mounted on an internal block wall. On the other side of the wall, a sort of 'enormous trunking' has been formed running from floor to ceiling (think it's probably plasterboard & timber) - this makes its way into the loft. At the top of this thing, there's big gaps to allow the cables out into the loft (and the draught from the eaves vents down into the trunking!).

Might be possible to stuff these holes at the top end with some fiberglass mat ......

Thanks Adrian

Why not just traditional balls of screwed up newspaper?

David

TLC sell the stuff & no warning appears on their site. I looked at Evodes site & no warning their or on the HSE data sheet.

I imagine expanding foam often comes into contact with cables - does it really have a bad reaction?

================================== Expanding foam usually requires some moisture to help it to expand, so there is a (slight) potential risk from whatever water you use. You might have to shut down your electricity for some considerable time to make sure that no water can get into your CU.

Cic.

Because, ideally, I'd like to fill in the hole that's behind the CU - and the only easy way to do this is by removing the cover from the CU and poking 'something' in from the front. Ideally this would be something thin, like the nozzle of an expanding foam can.

It's be a right old fiddle trying to push newspaper in past the MCBs..

Might be possible to do the bit in the loft this way - but maybe fibreglass mat would work up there...

Regards Adrian

That problem was with blown polystyrene insulation, the material leached the plasticiser out of the PVC insulation on the cable and made it very brittle. It doesn't happen with Polyurethane foam so you are OK.

Ah - that's good news - thanks !

Adrian

I was just going to say that! I think expanded polystyrene sheet can have the same effect. Since the cables should be well glued in place by the stuff then even if the PVC insulation were to become embrittled it wouldn't matter as it can't now move anywhere.

I suppose thermal insulation could be an issue, though. Perhaps the "fire-stop" type expanding foam (which won't burn) would be the counsel of perfection.

bear in mind most liquid compounds will conduct electrickery while wet.

NT

No reaction at all.

The only possible downsides are loss of heat transmission, which is peanuts on a short run anyway, and the fact that it's very 'permanent'.

Watched a couple of episodes of "Holmes on Homes" on Sky last week (he can build my house any day).

He is a great fan of spray foam (exanding foam on an industrial level), and he covers everything (wires and all) with it.

Those based on water as a solvent will, sure.

But not those based on organic materials, by and large.

Your regular builders "fill foam" cure by absorbing water. Usually water in the air, so there isn't any need to "splash it all over" Henry Cooper style.

Hi,

I was browsing old message to find out about foam (see my other post) and stumbled on this. I wonder if the foam cures in contact with water, would spraying water on foam with a plant mister be one way to halt foam in its tracks if it expands more than it should?

I'm certainly no expert, but I'd expect it to do the opposite. I'm sure I remember seeing it foam *more* when the surface was damp.

Pete