Routing Cable in Cavity / Air Gap

Discussion in 'Electricians' Talk' started by mackie, Nov 2, 2017.

  1. mackie

    mackie Member

    Hi, its me again.

    Scenario. Single skin exterior wall being studded out and insulated to change the room into an extension to the kitchen. 50mm airgap between single skin wall and 100mm studding.

    I want to run electrics down to new sockets to be installed in the wall, an afterthought now the stud work is up.

    My initial idea was to use 2 x 50mm celotex in the studding and channel down the middle, but reading the Celotex website this is a no-no.

    So is it ok to run / clip the cable down the inside of the single skin wall inside the airgap? Then through the Celtex at socket level filling round the wire / celotex with foam? Drip loop in the wire just to be safe in case of condensation?
  2. KIAB

    KIAB Super Member

    You won't be the first or last peep to do that, some don't even clip it.:)

    But, I wouldn't foam around the wire.
    mackie likes this.
  3. spinlondon

    spinlondon Screwfix Select

    The main concern with running cables in cavities, is that it might cause a bridge allowing moisture to track from one side to the other. Another concern is damage to the cables caused by debris falling onto the cables.
  4. Coloumb

    Coloumb Screwfix Select

    I've always thought it was due to the need to (possibly) de-rate the cable if cavity wall insulation is pumped in.
  5. Coloumb

    Coloumb Screwfix Select

    What's this about celotex mate? Got a link?
  6. JP.

    JP. Screwfix Select

    EPS insulation leeches the plasticiser from pvc cables with the consequence of worsening ir readings over time..hover Celotex and the like is not EPS.

    I rest my case
  7. retiredsparks

    retiredsparks Super Member

    That was certainly the main point. Along with no support. And the chance of water running down the cable into the inner skin/enclosure in the house.

  8. mackie

    mackie Member

    Look for Can I recess electric cables into Celotex?

    Jusd read it agan and the first reason is becuase it would reduce the performance of the Celotex, then it goes on to say cables should be oversized.
  9. mackie

    mackie Member

    No real chance of this. THis is a single storey single skin wall sealed to the roof at the top, so not main access for major debrie to enter the void
  10. Pollowick

    Pollowick Screwfix Select

    The comment from Celotex:

    Can I recess electric cables into Celotex?

    No. Electrical cables should not be channelled into Celotex as that would reduce the performance of the Celotex.

    Cables can penetrate through Celotex and if cables are laid between two layers of Celotex they should be oversized to cope with any increase in operating temperature.

    Celotex has no detrimental effect on the cable sheathing.

    The "good" thing about Celotex is the final comment - that it is not detrimental unlike polystyrene and some other insulation materials.

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