Hi everyone.

Putting cable in contact with expanded polystyrene is a bad idea,
because it causes the PVC insulation on the cable to become
brittle.

Can this, or any other problem, occur when running cable
next to other thermal insulants?

   Thanks,
   David Pearson.

In message <d6o2am$k1u$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com>,
  "David Pearson" <spam.lords@go.tickle.yourselves> wrote:


> Hi everyone.
> 
> Putting cable in contact with expanded polystyrene is a bad idea,
> because it causes the PVC insulation on the cable to become
> brittle.
> 
> Can this, or any other problem, occur when running cable
> next to other thermal insulants?
> 


Polystyrene (not just the expanded variety) somehow causes the
plasticiser to leach out of PVC (turning it into uPVC?). This is what
causes it to go brittle. It's a chemical thing and I'm no chemist.

There are other issues to worry about when running cable next to or in
thermal insulation, the most obvious being the thermal capacity and
hence current-carrying capacity of the cable. There are regulations and
guidelines about this, but to get a sensible answer you're going to need
to provide us with a few more details of your problem. For example, what
size cable on which circuit for how long over/under/in/through what kind
of insulation in what kind of installation.

Hwyl!

M.


-- 
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... REALITY.SYS Corrupted: Re-boot Universe (Y/N/Q)

"David Pearson" <spam.lords@go.tickle.yourselves> wrote in message 
news:d6o2am$k1u$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com...

> Hi everyone.
>
> Putting cable in contact with expanded polystyrene is a bad idea,
> because it causes the PVC insulation on the cable to become
> brittle.


The plasticizer leaches out into the polystyrene.
It shouldn't be a problem as the plasticizer causes the polystyrene to 
shrink away from the cable.

"David Pearson" <spam.lords@go.tickle.yourselves> wrote in message
news:d6o2am$k1u$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com...

> Hi everyone.
>
> Putting cable in contact with expanded polystyrene is a bad idea,
> because it causes the PVC insulation on the cable to become
> brittle.
>
> Can this, or any other problem, occur when running cable
> next to other thermal insulants?



There is no reaction with Kingspan, Celotex, Rockwool or fibre wool.

However bear in mind all of these insulate far better than polystyrene and
could cause the cable to overheat if laid poorly.

OK, thanks everyone.

The regs about putting cable next to insulators
are explained in Newnes, but I will
have enough room in the ventilation space between
the insulation and sarking for cable.

Hmmm..... can I put junction boxes in that space?
It will be venilated at eaves and a through-roof
ventilator, so condensation should not be a problem,
but it is one more thing to worry about...

Thanks,
David P.

dennis@home wrote:


> The plasticizer leaches out into the polystyrene.
> It shouldn't be a problem as the plasticizer causes the polystyrene to 
> shrink away from the cable. 


yes, I've seen various warning about the effects of polystyrene on pvc
insulation, a few weeks ago I came across an offcut of T+E that had been
 sitting under a polystyrene slab under my bath, certainly been there 15
years, probably 30. I was interested to see that the PVC seemed to have
had more effect on the poystyrene, the outer skin of the insulation had
gone a little scasly and flaky, but underneath that it seemed OK, the
polystyrene had as you say shrunk away from the cable, just like it does
with solvent based glues.

Of course I'm not saying ignore the issue and lay cables over
polystyrene, just that the damage to the cable that I found was faitly
minimal ...

In message <d6pe7d$5d4$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com>,
  "David Pearson" <spam.lords@go.tickle.yourselves> wrote:


> 
> OK, thanks everyone.
> 
> The regs about putting cable next to insulators
> are explained in Newnes, but I will
> have enough room in the ventilation space between
> the insulation and sarking for cable.
> 
> Hmmm..... can I put junction boxes in that space?
> It will be venilated at eaves and a through-roof
> ventilator, so condensation should not be a problem,
> but it is one more thing to worry about...
> 

If I have understood you correctly you are putting insulation in the
plane of the roof, and intend to run cables on top of that insulation?
What is the detail below the insulation? There is a big warning about
putting things like junction boxes (i.e. with screw terminals) in places
where they can't be inspected. Under floorboards is generally thought ok
as it isn't too difficult to lift a bit of carpet and lever up a
floorboard, but the classic no-no example is within a plaster/boarded
wall because you'd have to destroy the wall to find the JB.

Your over-the-insulation idea sounds a bit like the in-the-wall problem
I'm afraid.

Hwyl!

M.


-- 
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Run for your life!!