What junction box to use with armoured cable?

Discussion in 'Electrics UK' started by s999, 9 May 2005.

  1. s999

    Joined:
    5 Mar 2005
    Messages:
    38
    Thanks Received:
    0
    Country:
    United Kingdom
    This is where the armoured cable terminated, and then goes into normal 2.5mm T&E cable.

    The actual juntion will be indoors, do can I use a normal 30amp junction box or does it have to be one or those big expensive weatherproof junction boxes (that cost at least £5)?
     
  2. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,103
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    You don't need a waterproof box as it's not outside, but an ordinary JB is no use at all as you need to be able to mount a SWA gland on it, so you'll need one of those metal adaptable boxes.

    But if you think that £5 is "expensive" then I would caution you against doing any electrical work, as sooner or later you'll bodge something to save a few quid. It's going to cost you more than that just for a metal box and a set of glands - this is not something you should approach with the mindset that £5 is "expensive"....

    What are you supplying with the SWA? Is 2.5mm² big enough?
     
  3. Big_Spark

    Joined:
    20 Feb 2004
    Messages:
    3,434
    Thanks Received:
    1
    Country:
    United Kingdom
    Why not simply take the SWA to the origin of the circuit and terminate it in the Board. Other than I can only echo BAS's comments.
     
  4. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,103
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    I was assuming that, like most (all) CUs, it would be too flimsy and too cramped to terminate SWA in it.

    s999 - another Q for you - I take it you are using 3-core SWA?
     
  5. mapj1

    Joined:
    24 Nov 2004
    Messages:
    1,041
    Thanks Received:
    2
    Country:
    United Kingdom
    Almost any metal box will do - it is possible to go in to the back of a double socket box and blanking plate. It doesn't need to be weatherproof, but enough room to work in is useful. You are right about the tail wagging the dog with a plastic box, it is possible but not something I'd recommend without seeing the box first. If the metal box is along side the plastic CU or whatever, then the cores of the SWA can pass through the metal box that holds the gland, straight into the plastic one, without actually having extra joins in the metal box. Remember to bring an earth tail wire out to earth the box and the SWA armour though.
     
  6. Big_Spark

    Joined:
    20 Feb 2004
    Messages:
    3,434
    Thanks Received:
    1
    Country:
    United Kingdom
    All Consumer Units are not plastic, and those that are, not all are flimsy, although I accept that many nof the cheaper brands certainly are.

    We are not talking about a 4C16mm or 3C25mm here, we are talking about at most a 3C2.5mm, this is hardly much more than a bootlace and the strain it would put on any CCU would be minimal. As for being able to terminate a SWA into a Consumer unit due to room, what rot in my opinion, I have never had this trouble.

    If want to know how tight a board can be, try terminating 20 4C or 3C 16mm and several other largish SWA's into a TPN panel, then you know what tight is.
     
  7. s999

    Joined:
    5 Mar 2005
    Messages:
    38
    Thanks Received:
    0
    Country:
    United Kingdom
    First things first......... what does SWA stand for? :oops:

    £5 isn't a lot for me....... its just that I've got a normal 30amp junction at home and I'm wondering if theres any point in buying another one.

    I'm gonna run a 2.5 T&E from the consumer unit....... under the floorboards and then terminate it just as it reaches the back garden a wall........ and then the armoured cable come in.
     
  8. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,103
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    That's true

    It's bigger than 6mm² T/E. And isn't the gland size the same for SWA up to 6mm²?

    Well - there's no getting away from the fact that you've probably seen one or two more CUs than I have, ;) , but of the popular makes that represent 90% of the domestic market, is it reasonable to expect that you could retro-fit a 20mm SWA gland into the side/top/bottom of many of them?

    If it is then I'll apologise for misleading s999, but at the time, not knowing how adept he was, not knowing what CU he has, not knowing what kind of a rats nest is inside, not knowing what access around the outside is like and not knowing what experience of terminating SWA he has, I went for what I considered the more trouble free option.....
     
  9. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,103
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    Steel Wire Armoured.

    It's no use for this.

    And what happens then?

    Where does the armoured cable go, how does it get there, what load will it be powering at the other end, and what will be the total distance from CU to the far end? And is it 3-core?

    And do you know what sort of earth your supply has (TN-S, TN-C-S/PME or TT)? A description or photograph would be useful if you don't.

    And finally - are you aware of the requirements of Part P of the Building Regulations vis-a-vis running electrical supplies to gardens and outbuildings?
     
  10. s999

    Joined:
    5 Mar 2005
    Messages:
    38
    Thanks Received:
    0
    Country:
    United Kingdom
    ^ I don't know any of that....... all I'm gonna do is run the wires under the floorboards (because we're about to lay carpet soon and I don't wanna cause a mess later).

    I'm actually gonna get an electrician to connect it at the consumer unit and in the shed (where I want the power).

    I'm using 3 core T&E armoured cable.
     
  11. s999

    Joined:
    5 Mar 2005
    Messages:
    38
    Thanks Received:
    0
    Country:
    United Kingdom
    ^ Actually I do know the answer to all of that......... but I just said that I didn't for the hell of it.
     
  12. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,103
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    Well I suggest you use that knowledge to determine if 2.5mm² is enough before you put the carpet down......

    PS:

    Have you checked that he's happy with this? He'll have to sign it off to say that he designed, installed and tested the circuit, and if you just have him along to connect each end without any knowledge of what lies in between, you might be in for a nasty surprise.

    Like pick one:

    a) "No, I won't do it"

    b) "I'll have to rip it all up and start again"

    As I said, are you aware of the requirements of Part P of the Building Regulations vis-a-vis running electrical supplies to gardens and outbuildings?
     
  13. Big_Spark

    Joined:
    20 Feb 2004
    Messages:
    3,434
    Thanks Received:
    1
    Country:
    United Kingdom
    Ban, a 3 Core 6mm will require a 25mm Gland generally, although if you can get one of the larger 20mm from BICC then this may fit. 3C2.5mm will usually fit a BW20S gland, so whilst the gland thread size is the same as a larger or any other 20mm gland, the gland will be physically smaller and produce less strain on the consumer unit.

    Regarding the fitting of the 20mm gland to a consumer unit, if you have a 20mm Starrett cutter then you can fit one to any of them. The cables, regardless of type, should only ever enter a consumer unit in the top or bottom, unless you have trunking or some other enclosure covering the side opening...in an ideal world any way :D

    BAS, I don't think you misled anyone, or have anything to possibly apologise for, you gave good advise based on your personal experience and knowledge, no-one can criticise that. Your comment about S999 ability is very valid, and my personal feeling he is not competent to undertake the work he wants to do, if he was then he probably would not be asking these questions, so perhaps your answer was the best one here.
     
  14. plugwash

    Joined:
    28 Mar 2004
    Messages:
    8,818
    Thanks Received:
    265
    Country:
    United Kingdom
    well tlc said that a 20mm gland was right for 3 core 6mm and the 20mm BW glands they sent me were just fine with 6mm

    once you get into 25mm glands you either have to use a bloddy big box or make the holes yourself with a holesaw afaict
     

Share This Page