Pvc Cable And Thermal Boards (Polysyrene)

[monkey5]

Just a  question that i had pass through my mind earlier.  basically ive done a rewire and on the outside walls its being thermal boarded so ive capped everything in galv capping, working there today getting it finished off ready for plasterer to get started tomorrow.  i was a couple of lengths short and as its bank holiday the only places open were screwfix and toolstation, they both only keep pvc so turned away and will have to go first thing in the morning to finish off.

but is the reaction with the cable due to whats in the PVC - plastiser, if so does the pvc channel have the same "thing" in it or could you use pvc capping to protect the cable from the polystyrene.  i intend on finishing it off in galv but just thought id ask.

 

[SLIPSHOD & SLAPDASH]

I believe the plasticiser in the cable is pulled out by the polystyrene and there is not much of that in capping, especially the crap screwfix sells which breaks if you look at it wrong.

 

[monkey5]

i did actually have my elecsa assessment on friday and took the assessor to this job he was pleased i had capped it and told me about he parents house.  basically about 25 years ago they insulated the loft with polystyrene sheets, so some of the lighting cables were touching.  about 5 years ago he ripped it all out and the cable that was resting on top had sunk in to the polystyrene by about an inch and a half, the cable was watery like, he said it was really strange to see. will give him a ring tomorrow to ask the same question.

 

[steptoe]

mmmm

dont think by using capping you have negated the effect,

capping is NOT an enclosure,

you still have to work your cables as if they are covered in polystyrene, or whatever it is.

you should have put them in conduit.

 

[SLIPSHOD & SLAPDASH]

I think the capping was used to simply keep the polystyrene off the cables, not to help against thermal effects.

I have seen tw&e thats been laying on polystyrene for about 20 years. It had sunk in about 30mm and had gone brittle with bits of polystyrene melted to it.

 

[steptoe]

ah, ok, yes, I get it now, simply to alleviate the detrimential effect on the cable,

.

 

[monkey5]

Yes used simply as a barrier. So would PVC capping had melted in too?

 

[binky]

PVC capping probably would melt into polystyrene, but important point is that its off the cable so shouldn't be a long term issue. I did have a bit of cable in my van for about 2 years wrapped around a piece of polystyrene - it barely did anything, but cables in use are subject to thermal heating so might have increased detrimental effect. Polystyrene beads are defo a problem, which is what prompted the experiment.

 

[OnOff]

Is it that polyurethane spray foam though IS ok around cables or did I dream it? Something about the solvent evaporating so quick etc? Intumescent type of course!

 

[Steve3948]

You would think the plasterboard backed stuff would be ok, as it should be assumed that cabling will be in place where it will be used, and manufacturers would be mad not to take that into consideration.

I always channel anyway, just in case you need to pull a cable out, and with a dollop of fast fix on a clipped cable you have no chance.

 

[binky]

Is it that polyurethane spray foam though IS ok around cables or did I dream it? Something about the solvent evaporating so quick etc? Intumescent type of course!

chemically different