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Sub Main in Notched Joists. Your Opinion Please.

Zoomup
Here we have a 16.00mmm2 T&E cable installed many years ago in a house, and it supplies a recently renewed consumer unit in an annexe. The cable runs under the first floor boards in notched  wooden joists. The boards are about 15mm thick. There is no mechanical protection apart from the wooden boards. The cable runs centrally to the floor boards  in the notched joists.


What is your opinion about leaving the cable where it is? It is backed up by a 60 Amp fuse in a switch fuse. There is no R.C.D. protection for the sub-main cable.


Z.


  • 0
    Notched joists was standard practice when I were a lad. Just as long as the notch was centred under a board so the nails could go safely each side then it was fine (as everyone knew in those days that you only nailed near the edges of the board - as nailing just in the centre wouldn't stop the natural timber boards cupping/twisting and was likely to hit cables or pipes). Nails from more random things like gripper strips or carpet tacks shouldn't go all the way through a standard thickness board.


    Nowadays it's a no-no of course, but for an existing, I'd suggest no worse than a C3 (e.g. similar cable concealed in wall without 30mA RCD protection, although the risks are probably somewhat less).


      - Andy.

  • 0
    As you know, it falls foul of 522.6.201.


    I agree with Andy, were you doing an EICR, it would be C3.


    On the whole, I think better for the structural integrity of the house to leave it where it is; but if you are feeling energetic, you could drill some holes (1/2"?) through all the joists and re-site it.


    If some prat puts a nail through it, so be it.
  • 0
    Chris Pearson:

    As you know, it falls foul of 522.6.201.


    I agree with Andy, were you doing an EICR, it would be C3.


    On the whole, I think better for the structural integrity of the house to leave it where it is; but if you are feeling energetic, you could drill some holes (1/2"?) through all the joists and re-site it.


    If some prat puts a nail through it, so be it.


    I am not inclined to reduce the strength of the  wooden joist any more Chris by drilling. The cable is large, about the width of a man's thumb.


    Z.


  • 0
    Zoomup:

    I am not inclined to reduce the strength of the  wooden joist any more Chris by drilling. The cable is large, about the width of a man's thumb.


    As I am sure you know, the French translation of "an inch" is "un pouce", which is also their word for a thumb. But that is length, not breadth. I have just measured my own thumb with my super-accurate Mitutoyo callipers and it is exactly, if not precisely, 1/2" wide.


    I actually would not worry about drilling 1/2" holes, but it is hard work and gives me blisters. I agree - stick with what you have. ?


  • Former Community Member
    0 Former Community Member
    Chris Pearson:



    were you doing an EICR, it would be C3.


    On the whole, I think better for the structural integrity of the house to leave it where it is; but if you are feeling energetic, you could drill some holes (1/2"?) through all the joists and re-site it.


     


    Hi Chris, it would be an unusual code for the majority of EICRs limitations do not include lifting all floorboards to inspect cable routing! 


    BTW, are you using a bit and brace to drill holes? 


  • 0
    Weirdbeard:
    Chris Pearson:



    were you doing an EICR, it would be C3.


    On the whole, I think better for the structural integrity of the house to leave it where it is; but if you are feeling energetic, you could drill some holes (1/2"?) through all the joists and re-site it.


     


    Hi Chris, it would be an unusual code for the majority of EICRs limitations do not include lifting all floorboards to inspect cable routing! 


    BTW, are you using a bit and brace to drill holes? 




    No, but Zoomy seems to have them up already.


    In tight spaces, I have a wee auger (mentioned in the old forum IIRC) which I can drive with a 1/4" socket. It works well, but after 3 or 4 joists, it is apt to give me a blister on the web between my thumb and index finger. I suppose that I could wear gloves! ?


  • 0
    If you're feeling keen, you can get metal plates designed to go above a joist notch to protect cable/pipework
  • 0
    wallywombat:

    If you're feeling keen, you can get metal plates designed to go above a joist notch to protect cable/pipework


    I have some of those plates. I doubt they would stop anything bigger than a panel pin! If they were any thicker they would lift the board.


  • 0
    Many years ago my inspector suggested metal BESA box lids , slightly recessed and fixed either side of slot with screws. You would have to drill through those!
  • 0
    decent safe plates are available from good wholesalers.I think they are 2mmthick.  sounds flimsy but they are pretty study.  They might need dropping into the timber if they lift the board.


    Gary

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