I will shortly start building my ICF house here in the UK and I have a question about running the electric cables in the foam.

The type of cable that is not affected by the polystyrene foam does not seem to be widely available in the UK (or at least I can't find it!) and so I am going to run the cables in conduit.  My question is whether the problem about the polystyrene affecting the plasticizer in the cable sheath only applies if the cable is in direct contact with the polystyrene or whether close proximity is enough to affect it.

More specifically, the shape of the cable entry hole in the electrical box is not round so the conduit will stop just above the electrical box and the entry point won't be sealed.  I don't think that the cable will touch the polystyrene but it won't be sealed from it.  Is that OK?

Thanks for your help.
Andrew

problem about the polystyrene affecting the plasticizer in the cable sheath

Where did you hear that?

It's pretty common knowledge.

This is from the PolySteel UK web site:

"We recommend that the use of Low Smoke Zero Halogen (L.S.0.H) cable for wiring throughout your home as this is not affected from migration or leaching which occurs with EPS.  The good news is that the L.S.0.H cable should not cost more than standard cable and we are able to offer advice on supply and costs. Ref (IEE Regulations 16th Edition, which calls for upgrading of cable capacity, which is necessary because of insulation surrounding the cable). "

Polarwall say:

"Electric cables: care should be taken to ensure that the polystyrene does not come into contact with any electrical cables, as the plasticizer in the cable sheathing will migrate to the polystyrene.  Therefore all cabling should be enclosed within a conduit channel."

The HotWire Direct web site says:

"Since most organic solvents attack expanded polystyrene, particular care must be taken in the choice of adhesives, paints, coatings, and mold release agents. Plastics containing plasticizers (e. g. flexible PVC) should not be kept in contact with expanded polystyrene because of the risk of plasticizer migration."

I don't know about the USA but in the UK electric cables for household wiring are made with a PVC sheath that contains a plasticizer. 

Much of the home wiring used in the US has a nylon jacket over the PVC insulation and overall jacket material.  This keeps the plasticizer in the PVC.

An example is Southwire Romex SIMpull NM-B electrical cable.  Construction of this wire from inside to outside is:  copper conductor, PVC insulation, Nylon jacket, paper wrap over all conductors and ground, PVC overall cable jacket with Nylon outer layer/jacket.

http://www.southwire.com/ProductCat...sheet6

Using this type of home electrical wire would not result in contact between the PVC material and the polystyrene ICF insulation.

Well you learn something new every day! Thanks for that.

aa_uk;

are you talking about the romex sheathing or  the wire insulation, if it migrates to EPS what exactly is it doing that is harmful.

This may be common in the UL , but first I have heard of it and am not grasping what the long term damage is?

all OSB sips EPS are in contact with romex

I had thought that something in the EPS damaged the outer sheath of the cable but reading the HotWire piece I think that it is the other way round and I assume that the plasticizer in the PVC outer cable sheath of UK cables "melts" the foam with which it comes into contact.  From the sound of it, it is only an issue in the UK because our cables are manufactured differently to those in the USA.  We don't have the nylon outer jacket, we have a PVC outer sheath that surrounds the PVC covered individual wires.  Looking at the picture of the Romex SIMpull cable we don't have the outer yellow bit.

aa_uk;

if you have armored cable in the UK it would solve your problems