Protecting wiring

[Matty F]

My house was rewired 20 years ago. The insulation in the ceilings and walls is fireproof foam. Nobody at the time knew that the foam would degrade the wiring, as it is doing.

I'll pull off the corrugated roofing iron and wooden weatherboards where necessary to fix it. There isn't much wiring involved. There's a timber frame.

I was wondering if I can just put building paper under the wires where they lie on the foam in the ceilings. And maybe more building paper in the walls. There is already building paper immediately next to the roof and weatherboards.

[Andrew Gabriel]

In what way? PVC is pretty resistant. Some plastics will leach out the plasticiser, but I suspect in that case it's probably better not to do anything which moves the wiring.

[Matty F]

I've read about this problem many times. I'm prepared to replace the wiring if it's damaged. Since most wiring in NZ houses touches building paper I guess I'll just put building paper between the wiring and foam.

"Polystyrene insulation

If in direct contact with electricity cables, polystyrene insulation can cause the coating on the cables to harden and crack, creating a fire or electrical safety risk. To avoid this, polystyrene insulation must not get into direct contact with any PVC coated cables. They should be separated using self-adhesive paper, polyethylene or polypropylene tape between the PVC and polystyrene, or by installing the cables through conduits."

[sm_jamieson]

"Foam" is not usually polystyrene, at least not in the UK. Simon.

[Matty F]

,

Well my foam is polystyrene.

[Matty F]

OK so I've got the roof off. Here's a photo of the wiring to the light in the middle of the ceiling.

wire had sunk deep into the polystyrene foam, and the wire covering is a bit soft but seems OK. I have put thick building paper under the wire wherever it goes.

But why did the wire sink into the foam? It's a short lighting circuit to a single socket in the ceiling. At most it would have had a 100 watt bulb in it, and for the last 5 years, a 20 watt CFL. So, less than half an amp melts the foam.

[ARWadsworth]

It's a chemical reaction between the polystyrene and the cable, not heat that caused that.

[Matty F]

OK that's probably it. Look's like I'll be taking the rest of the house apart.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember sm_jamieson saying something like:

It's very common - as Aerobord, etc.