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Topic Title: Polystyrene insulationand pvc
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Created On: 01 November 2016 09:36 PM
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 01 November 2016 09:36 PM
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ScoobyDoo

Posts: 23
Joined: 30 March 2016

I was in a loft today which had about 4 or five inches of little polystyrene balls insulation under a load of rock wool stuff. The little balls were sticking to the cables all over. I'm going to talk to the customer about it tomorrow but I wondered does anyone know how long it takes for polystyrene to break down pvc insulation?
 02 November 2016 08:25 AM
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di515223

Posts: 337
Joined: 08 July 2010

Be very careful there, polystyrene typically leaches the plasticiser from PVC, leading to the insulation being brittle if disturbed.
I doesn't take long to start the leaching, and things like temperature have an effect, so it is difficult to say if there is a safe duration.
(this is why mains leads are put is those silly plastic bags when you buy an appliance these days - to protect the cable and connectors from the polystyrene packaging) I would not disturd any cabling with the power on, as I have seen the insulation crumble like a biscuit when someone tried to move a T+E that had been exposed to polystyrene, leaving them with great chunks of insulation falling off!
Unfortunately, you are unlikely to see any electrically testable effects until the cable is disturbed, as the insulation typically stays in place with a good IR until disturbed.
I wonder how many fires have started this way - lob a suitcase up into the attic, disturb a cable and leave bare conductors sitting in flammable materials in an unnoticed position for however long it takes for a mouse or something to create a short?

Dave
 02 November 2016 10:20 AM
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justinneedham

Posts: 90
Joined: 21 January 2005

There are plenty of houses about also using polystyrene beads in the cavities. (I don't think it's used these days?). These are often those late-Edwardian type places where it's quite common to also find cable drops within the cavity.
Personally, I've only ever found cables "sticky", from polystyrene, but have found plenty of UV'd T&E with insulation crumbling off.
 02 November 2016 10:56 AM
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normcall

Posts: 8520
Joined: 15 January 2005

I've seen the beads take the insulation off and leave bear metal shining through the holes.

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Norman
 11 October 2017 12:00 PM
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tjs2

Posts: 50
Joined: 05 February 2005

Originally posted by: justinneedham

There are plenty of houses about also using polystyrene beads in the cavities. (I don't think it's used these days?).


FWIW, this is quite widely used still (more commonly now polystyrene beads with graphite added - they have a grey/silver appearance).

Compared to the white fluff, they insulate better, soak up less water and are better at filling narrower cavities. I've also seen them used on new-build.

I thought the effect on PVC cable insulation depended on the type of plasticiser used in the cable - with older cables generally being more susceptible?

Also be careful for XPS (extruded polystyrene) insulation with is also polystyrene foam, but looks more uniform (not made up of fused beads like expanded polystyrene is), and seems to be frequently dyed different colours too.
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