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Wall Cavity Wiring.

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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.
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  • 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.

Reply
  • 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.

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