Expanding foam on T&E

[Jacka]

Hi all

I'm currently in the process of finishing off the last room in my house. It's a bedroom above a garage, which was part of an extension built before I bought the house. After removing all of the skirts, there's large gaps which I think causes drafts. I'm planning to use expaning foam, but there's a cable run for one of the sockets.

Am I ok to expaning foam over the top of it or is it a no no?

Thanks

Jacka

 

[PrenticeBoyofDerry]

It would depend upon the type of expanding foam.
If polyurethane foam, you should be okay.
A concern would be if the cable runs horzontally behind the skirting rather than vertically as this would not be good practise.

 

[JohnW2]

I'm planning to use expaning foam, but there's a cable run for one of the sockets. ... Am I ok to expaning foam over the top of it or is it a no no?

A few years ago, I asked this very question of a few manufacturers of expanding (polyurethane) foam. Somewhat surprisingly (given that they are usually very cautious in 'protecting their backsides') they all assured me that there was no problem with expanding PU foam in contact with PVC wiring cables.

Contact between expanded polystyrene insulation and PVC cables is a no-no.

There are theoretical (thermal) issues, which some here may wish to raise, associated with any sort of insulation (no matter what the material) around electrical cables - but if you are talking only about very small lengths of cable, it is IMO unlikely to be a major issue.

Kind Regards, John

 

[stillp]

Interesting. I asked some cable manufacturers the same question some years ago and they told me the opposite!
To the OP, I wouldn't take the chance - put the cable into mini-trunking if you must leave it there.

 

[JohnW2]

Interesting. I asked some cable manufacturers the same question some years ago and they told me the opposite!

How odd. As I said, that's more what I would have expected ('CYA'), but it's not what I experienced.

To the OP, I wouldn't take the chance - put the cable into mini-trunking if you must leave it there.

I suppose that's the surest approach - but, FWIW, I've had PVC cables in contact with PU foam for at least 25 years, with no apparent deleterious effect. In contrast, I've seen the effects of the expanded polystyrene/PVC cable combination much earlier than that.

Kind Regards, John

 

[riveralt]

Am I ok to expaning foam over the top of it or is it a no no?

As above regarding the type of expanding foam to be used.
The OSG states that sheathed cables must be separated from expanded polystyrene materials to prevent take-up of the cable plasticiser by the polystyrene as this will reduce the flexibility of the cables.

It also will depend on the length/depth of the foam insulation used, the size of the cable and its intended use.
For example 1mm² T&E lighting circuit inside 100mm of foam insulation no problem.
6mm² T&E cable on a 8.5kw electric shower inside 100mm of foam insulation - could be problems.

 

[JohnW2]

As above regarding the type of expanding foam to be used.

I don't think that the OP actually has any choice, since I very much doubt that he would be able to find any expanding foam sprays other than polyurethane. I don't think expanded polystyrene (which would be a problem) exists as a spray - at least, not for non-specialist use (and I'm not at all sure that it exists at all). I agree with the rest of what you write.

Kind Regards, John

 

[viewer]

Recently took out some T&E cables which had been covered in polyurethane expanding foam about 10 years ago. They were fine.

 

[JohnW2]

Recently took out some T&E cables which had been covered in polyurethane expanding foam about 10 years ago. They were fine.

Indeed. As I said, I can top that with ~25 years in PU foam - and, again, the cables were fine. Conversely, I've removed cables that had suffered appreciably in <5 years when in contact with expanded polystyrene sheeting - still seemingly 'OK' (and test OK) if not disturbed, but with the PVC very brittle, and hence probably at risk of crackling/crumbling if significantly disturbed/handled.

Kind Regards, John

 

[Chri5]

Why not use rockwool and have the cable sitting on top?

Easier to handle and not so permanent that in future years the area isn't inaccessible.