Expanding foam and PVC cable

IET Forums - expanding foam + pvc (theiet.org)



Also, do not accidentally spill petrol on your Stanley plastic organiser boxes. It makes the plastic brittle and cracks it.

Z.

And.......

Does Expanding Foam Damage Wiring? | Your Own Architect


Z.

Yes Z thet is called stress corrosion cracking, any solvent will do that and petrol contains benzine which dissolves lots of plastics, and it very effectively removes the plasticiser from PVC.

I wold not expect that cured foam would affect PVC, anyway as you are not moving it around it won't cause failure. It is the foaming agent in expanded polystyrene that damages PVC.

I think that is unlikely to be correct Z, imagine how many windows would fall out if the frames are seriously attacked! He is confusing polyurethane with polystyrene, quite different.

If this is twin and earth cable with an outer jacket, and not just insulated single cores, I'd not be that worried. Depending on the formulation of the foam and it's propellant, it may embrittle the outer jacket a bit, so if ever the foam is dug out, there may need to be a cable replacement, but then there may be anyway, depending how it is dug out, a problem for the future.

However, the inner cores will not be damaged, and even if they to became brittle, they cannot be flexed in side the foam, so the risk is minimal.

There certainly are foams, probably the majority, that are no issue at all, we use them to encapsulate certain types of wiring when resin would be too heavy.

IF the exposed cable is already running hot, then there may be a concern that the foamed section cannot dissipate its heat so easily but that is unusual in a domestic setting.

Mike.

I removed an old bit of coax that had been run under a UPVC window at home a few years back. It had been there for well over 20 years. The sheath in contact with expanding foam under the window was in better condition than the cable indoors, which was relatively OK - and of course both in far better condition than the sheath of the parts of the cable exposed to UV, where the sheath was rather stiff (but still OK).

Years' ago I wired three very TALL brand new, (each one being just one home / house), houses, in London.. 


Once all of the works was completed I was called back, (as I was the electrical contractor). On the ground floor there were ducts, where we could run our cables... these ducts were then filled with loose foam particles, (don't know why as it was on the floor - maybe to ward off damp)? 


All of the cables, that were covered in these loose foam granules, had started to 'blister!' 

I told them that they'd better remove the granules and change the cables... I had no further involvement in any further works there!


So, be careful!


regards... Tom

That was polystyrene granules, Tom, see above.