Forum home Road cycling forum The bottom bracket

Electrical cabling & Spray foam insulation?

I have a extension cable that goes through a partition wall via some of that cable trunking, Its not a perfect job but for what is needed its fine and looks quite neat.

Since then we have done some insulation work and the foam is now covering about 8" of the cable where it goes through the wall. The full cable is 3M long

My question is given that a small section of cable is fully covered with spray foam (8") is that going to cause a fire hazard?

A few points to note:

* The extension cable is 13A and was brand new from Curry's so meets all safety standard
* The extension cable is fully wound out i.e. its fully extended along skirting board trunking not coiled up anywhere
* The extension cable is powering the following on the other side of the wall - 1 x laptop charger (65w) and 1 x wall mounted fan heater (1500w on max usually only on low at 800w)

So if everything is on full then I am using 1565w total.

Is this safe?


  • davidofdavidof Posts: 2,919
    mr_eddy said:

    Is this safe?

    You sound like a German dentist !

    if the foam caught fire what would the consequences be? Would it just burn out and blacken everything?

    Your cable is carrying about 7 amps, I can't see it even getting warm so there is no reason for it to suddenly burst into flames.

    Electrical fires are often down to poor contacts in sockets or shorts etc causing local heating. Is the cable protected by a circuit breaker? In that case a short should not be possible.

    So I would say the risk is acceptable.
    BASI Nordic Ski Instructor
  • lesfirthlesfirth Posts: 1,365
    i would say the risk is less than negligible.
  • step83step83 Posts: 4,170
    Minimal risk, if the cables rated for that level of juice the cores will be a 1.5mm or something so you wont even feel the cables getting warm.

    You can slap an RCD on the end going into the wall as David said unless the extension lead has a build in one.
  • photonic69photonic69 Posts: 1,877
    Some foam, especially if it contains Polystyrene can leach the plasticisers out of the insulation covering of the cable, causing it to perish. Can you not remove the cable, drill a 25mm hole and line it with a length of 22mm overflow pipe and then thread the cable back through that? That's what I would do.
    "If" for any reason there was a house fire even if not directly related to the condition you describe then an insurance company might raise doubts over the electrical safety.
  • oxomanoxoman Posts: 11,320
    You shouldn't have an issue as all modern spray foams should be none flammable. Up until a few years ago we would use it all the time. Recently though we use different means of sealing voids around cables. Year's ago cavity wall insulation was considered a risk but didn't really cause much hassle. Biggest problem with the the spray foam is it sticks like 💩 to a blanket and is a pain to clean off anything. 30yr plus as an electrician so hopefully I've seen most things in that time.
    Too many bikes according to Mrs O.
  • mr_eddymr_eddy Posts: 830
    Thanks for replies, sounds like I am all good then. Will fret no more!
  • darkhairedlorddarkhairedlord Posts: 7,178
    bit of a bodge mind.
  • oxomanoxoman Posts: 11,320
    Not the best way to do it, but better than some I've seen in the past. Rather than small fan heater you could consider tubular heaters at approx 60 watts per ft and better for long-term background heat. Don't go plugging tumble dryers and stuff like that in either or things will warm up a bit.
    Too many bikes according to Mrs O.
Sign In or Register to comment.