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Wall Cavity Wiring.

Zoomup
Good morning on this bright and sunny start,


                          Q. Which regulation(s) specifically prohibit(s) the installation of cables in brick and block cavity walls within the cavity?


in a, Older premises?


    b, Newer premises?


If regulations exist, what reasons are provided for the prohibition? Or are we just concerned about chemical damage of cable insulation if the cables are in contact with some types thermal insulation?


Z.
  • 0
    Lack of support, bridging the cavity, but the one that kills the cables are those polystyrene balls!
  • 0
    Mornin' Colin, Street light columns used to have a long length of 1.5mm2 T&E run from head to bottom with no internal supports for the cable with no problems. Surely 2 or 3 meters for a cable drop in a cavity won't strain it?


    Vertically run cables in a cavity may not bridge the cavity. Wall ties do.


    There is not always P.V.C. insulation involved. It may come later but we don't know that.


    And the regulation numbers are?


    Z.
  • 0
    Should electricians not run cables through external cavity walls at all? Like this......

    https://www.youtube.com/watch?v=brb4K1o7suA


    Regulations please?


    Z.
  • 0
    I suspect no prohibition in the wiring regs apart from the fact that cavity insulation arrangements may make calculating a current rating a bit tricky.  Building regs like things crossing the cavity to be arranged to not cause un-necessary bridging. A quick nip across for an outside light is fine,  assuming not drilled up hill and filling with water, and I suspect a short drop between two  indoor sockets is OK too assuming it is well done,and not stuffing the cavity with loads of tangled slack . 

    I have seen plastic flex-conduit on wiring in a cavity with a foam infill, so I assume that was done to avoid questions of chemical compatibility.

    It does not feel like good practice, but I do not think it is an immediate fail in all cases

  • 0

    Street light columns used to have a long length of 1.5mm2 T&E run from head to bottom with no internal supports for the cable with no problems. Surely 2 or 3 meters for a cable drop in a cavity won't strain it?



    Depends how it's supported at the top. I think the general rule of thumb is that drops of up to 5m can be self supporting - but you do need a good (usually rounded) support at the top. Being bent around the top edge of a (possibly cut or drilled) brick probably isn't quite as good in that respect.


    Vertically run cables in a cavity may not bridge the cavity. Wall ties do.



    Wall ties are specifically designed to 'drip' in middle of the cavity - so they can't bridge water from the outer leaf to the inner one (at least if they're properly installed and aren't covered with mortar snots) - unless you can be 100% sure you cable can't touch the outer leaf and then the inner one on its way down it could form very effective bridge to carry water into the house.


      - Andy.
  • 0
    522.8.1
  • Former Community Member
    0 Former Community Member
    523.9; 522.8

    the above provide guidance but do not prohibit. 


    Regards TS
  • Former Community Member
    0 Former Community Member
    You can add 528.3.1 to the above too.


    Regards TS
  • 0

    AJJewsbury:




    Street light columns used to have a long length of 1.5mm2 T&E run from head to bottom with no internal supports for the cable with no problems. Surely 2 or 3 meters for a cable drop in a cavity won't strain it?



    Depends how it's supported at the top. I think the general rule of thumb is that drops of up to 5m can be self supporting - but you do need a good (usually rounded) support at the top. Being bent around the top edge of a (possibly cut or drilled) brick probably isn't quite as good in that respect.


    Vertically run cables in a cavity may not bridge the cavity. Wall ties do.



    Wall ties are specifically designed to 'drip' in middle of the cavity - so they can't bridge water from the outer leaf to the inner one (at least if they're properly installed and aren't covered with mortar snots) - unless you can be 100% sure you cable can't touch the outer leaf and then the inner one on its way down it could form very effective bridge to carry water into the house.


      - Andy.

     




    Where is all of this water coming from Andy?


    Z.

  • 0

    sparkiemike:

    522.8.1




    Damage to cable sheaths can be avoided by careful installation.


    Z.

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