The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 9 replies
  • Subscribers 31 subscribers
  • Views 1076 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

junction box size and location in ceiling void.

Former Community Member
Former Community Member
I am currently in the position of rewiring several sets of downlighters for a large kitchen / diner / living area.


There is currently a pretty awful setup of 'choc' connectors screwed to a joist and then a cats nest of cabling to this from/to the various zones of lights.


Clearly going forwards this is not acceptable and given that the whole ceiling is down at present I am keen to put this right.


I am planning on terminating the cabling in a junction box. All of the 1mm2 t&e is now installed and I would like to use the wagobox XL, however the joists are only 170mm in depth and pretty much any junction box which offers enough space to comfortably perform all the connections required would put the junction box within 50mm of the top or bottom of the joist. 


Could someone point me in the right direction to understanding the rules of junction box placement in this context? I cannot see anything in my on site guide.


Many thanks


James
  • 0
    A couple of ideas

    put a cross- batten between the joists and screw the JB flatways to that. Or let it float, so that like the cable when the ceiing is spiked it gets pushed upwards.

    Or make it not concealed by having some sort of access hatch - a plaster board box and a blanking cover can be used. Take photos for the next man in and leave them at the origin...

    Mike
  • Former Community Member
    0 Former Community Member
    Thanks Mike


    I hadnt considered that I could rotate the junction box through 90 degrees and install it on a batten facing down.


    Nice lateral thinking there :) thank you kindly.


    James
  • 0
    Also the 50mm limit is just for cables running through holes in joists - it doesn't apply elsewhere e.g. in the general void.

      - Andy.
  • Former Community Member
    0 Former Community Member
    AJJewsbury:

    Also the 50mm limit is just for cables running through holes in joists - it doesn't apply elsewhere e.g. in the general void.

      - Andy.




    That's interesting, because you are the second person to say this but this wasn't how I interpreted the detail in the on site guide, which says:


     



    "Where a low voltage cable is installed under a floor or above a ceiling it must be run in such a position that it is not liable to be damaged by contact with the floor or ceiling or the fixings thereof. A cable passing through a joist, under floorboards or ceiling support must



    (a) be at least 50 mm from the top or bottom, as appropriate, or"


    Which I took to mean if a cable is passing through a joist or under floorboards or above a ceiling support.


    Does it actually mean - "A cable when passing through a joist that has or will have floorboards or a ceiling attached to it must (a) etc " ?


    This would explain why I am getting this answer of it doesnt matter where your cables are clipped to the joist.


  • 0
    The idea is that if you nail or screw a floor board or ceiling to a joist, the nail or screw is unlikely to penetrate more than 50 mm. granted there may be the odd noggin, but other than in error, I do not see why a screw would be placed elsewhere.
  • 0
    I have never interpreted it like that.  I have always included the cables clipped along the joist as they could easily be nailed if someone misses with a nail or screw, which is pretty easy to do.  



    Gary
  • Former Community Member
    0 Former Community Member
    aligarjon:

    I have never interpreted it like that.  I have always included the cables clipped along the joist as they could easily be nailed if someone misses with a nail or screw, which is pretty easy to do.  



    Gary


    Interesting again! - So you include the clipped cable in the 50mm rule as per my original interpretation?

     


  • 0
    If you do not clip the cable, it will jump out of the way as the nail comes through... if you hold it tight, it cannot escape.

    Join the campaign for not using too many cable clips...

    M.
  • 0
    Had the same issue in my home, i installed a cross baton between the joists which worked perfectly when installing the joint box, i also made a purpose cut screwed down trap in the floor above so as to access the J.B should it be required without the need to take up full floor boards.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines