PVC Cable and Polystyrene Insulation

[AndyNewBuild]

Hi All,

I'm having a log cabin wired at the minute and have run into a slight problem with the cabling. Before anyone asks, yes this is being carried out by a Part P qualified electrician!

I want to run the cabling in the cavity between the two log skins but the cavity has expanded polystyrene insulation. Due to chemical interaction between PVC sheathed cable and polystyrene, you can't put this cable in direct contact with polystyrene. The solutions are to use suitable conduit or wrap the cable in polypropylene or polyethylene tape. Using conduit isn't practical as the space between the cabling and insulation is tight allowing just the cable up between the log skin and insulation. Using tape is possible but fiddly to get an even coat round the cable and avoid any bare spots exposing the PVC sheath.

I've come up with an idea which may work and would appreciate anyone's thoughts. I've looked around and found heat shrink sleeving made from polyolefin. This would be easy to slide over the cable and heat seal making a perfect barrier between the PVC and polystyrene.

Anyone see any problems with this?

 

[Chri5]

That's one way.

Why can't you cut a 25 x 25mm track in the polystyrene and use either conduit or flexible copex sat in the track.

It has a advantage in as much as you will be able to replace the cabling in years to come.

I appreciate what your trying to do, but bespoke work shouldn't be necessary and on the assumption that the polystyrene is likely to be 100m deep, cutting 25mm out really isn't going to drop the thermal ability of the stuff that much.

What do you intend to do with the socket back boxes ? Will they be surface over the log skin or do you intend to do some sort of flush mount?

 

[holmslaw]

..

 

[AndyNewBuild]

Thanks for the quick reply, much appreciated.

Unfortunately I've already bought all the standard cable and the install has started. My own fault for not checking with the electrician first regarding the insulation type - we live and learn . Just trying to find a solution which is cost effective and easy to carry out.

I'll try giving the company you suggest a call. Thanks for the lead.

 

[holmslaw]

..

 

[AndyNewBuild]

Log cabin company I spoke to hadn't been aware of the problem!

The insulation has already been dropped down the cavity. I've drilled the internal holes and have pull cords ready to pull the cabling through. Hose pipe might work although not sure if it's got a PVC plasticiser in it as well. Heat shrink sleeving is cheap and would be very flexible and easy to apply.

Will see what the tech guys say from the cabling company. Have also emailed a company which supplies heat shrink to see if they know more.

 

[JohnD]

you can also get flexible conduit - very easy to install - it's like a convoluted plastic hose. roomy enough to pull cables through after build. 20mm round should suit you.

 

[electronicsuk]

Will see what the tech guys say from the cabling company. Have also emailed a company which supplies heat shrink to see if they know more.

I'd stay away from heatshrink. Aside from the obvious fact that you have to heat it up to shrink it, potentially damaging the cables, it's also not as flexible as you might imagine when shrunk.

 

[AndyNewBuild]

Well I've had a play around with it on a piece of 2.5mm mains cable and it seems as flexible after as before. I've used heat shrink extensively in the past in electronics and the flexibility is always good provided you've used the correct type of heat shrink! There are various grades, some being much more flexible than others.

 

[ban-all-sheds]

Before anyone asks, yes this is being carried out by a Part P qualified electrician

Should have got him to install the cables. Surface mounted pyro would have been ideal for the log cabin.

I'm sure RF would agree...

 

[AndyNewBuild]

Yes but surface mounted is ugly! I like cables hidden. Yes makes it more difficult but it looks much better when finished.

 

[electronicsuk]

Yes but surface mounted is ugly! I like cables hidden. Yes makes it more difficult but it looks much better when finished.

You think surface mounted, unsheathed pyro is ugly?! Good god man!

 

[RF Lighting]

Some people have no taste...