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60 Amp Junction Box.

Zoomup
Mornin' All,

                      I came upon a burnt out terminal on a Crabtree ceiling 50 Amp. shower cord switch yesterday. The cables had become so hot after 3 years of use that the line P.V.C. had completely fallen off the conductor and had left a horrible black smelly sticky mess.


I had to replace the shower cord switch, but the damaged cable was then too short after removing the softened copper and damaged insulation.


So I had to make a trap in the room upstairs, which turned out to be wooden boards over other wooden boards to access the cable below with a view to lengthening one cable. I used a new 60 Amp junction box as it allows two large conductors to overlap and be secured by 4 screws. It is solid and of good quality.


It is this item.....

https://www.toolstation.com/60a-junction-box/p98775?store=N2&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&gclid=EAIaIQobChMIufLP1ZD25gIVybTtCh2YWAeiEAQYASABEgJZkvD_BwE


Z.
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    One may also wonder why this cable got hot and burned up its insulation. This will certainly be due to a loose connection, and probably a screw left loose or very low clamp pressure. Crimp connections are much more reliable than screws, provided the correct crimp and crimp tool is used.




    What a lot of bother using crimps, heat shrink sleeving, a hot air gun and still you have to house the big ugly joints, no, I prefer an all in one 60 Amp junction box with strain relief clamps inside. There is nothing wrong with well installed screw terminations as used for many years. Millions of electricity meters use screw type terminals.


    The heat was produced by a terminal screw not being tightened properly, or a bad switch contact. The Crabtree 50 Amp double pole ceiling cord switch has terminals located so that they are difficult to check if the switch is located next to a wall, as most are in bathrooms. The terminals are also single screw only which is a weakness in design. Even if the screws are tightened with the switch hanging a little way off the ceiling before fixing, a terminal can become lose if the switch is rotated when screwing it up to the ceiling. Then perhaps three screws can be checked for tightness, but the fourth is inaccessible as it is too close to the wall to test for tightness.


    Z.


     

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    It is your definition of "crimps" that is at fault then Z, perhaps you are thinking of yellow ones and some shoddy crimp tool which does not work properly. This is an ideal place to use proper tube crimps, and the correct crimp tool. Larger crimps are of course available, I rather like the ones for 400mm2 cables with M20 bolt lugs, as they enhance any domestic job, but then perhaps I am too purist! The cost of the hydraulic crimp tooling is also somewhat high, but once one has it there is a captive market.


    One may also wonder why this cable got hot and burned up its insulation. This will certainly be due to a loose connection, and probably a screw left loose or very low clamp pressure. Crimp connections are much more reliable than screws, provided the correct crimp and crimp tool is used.
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    Zoomup:




    AJJewsbury:




    There is a world of difference in a 40 Amp. shower load and a lighting load of a few L.E.D. lamps Andy, as well you know. The possible heating effects are totally different. You are cross threaded. There is no way that the lighting cables could contact the metal light switch plate insulted or uninsulated due to physical separation.



     You never mentioned the the lighting circuit for that metal switch was dedicated to just a few LED fittings 


      

     




    You never asked. Just how may lights would you expect a light switch to operate in a small refurbished flat?


    Z.


     




     

    If it’s to Building Regs no more than six.


    Andy B.
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    In this article they nod to the issue of interpretation of accessible.


     



    I believe that the wiring regulations have always required joints and junction boxes to be accessible for inspection or possible future alteration. Junction boxes should not be hidden in walls and plastered over as I have found on many occasions. A box and blank plate would be a better solution if the customer allows it. The Regulations for the Electrical Equipment of Buildings 14th Edition revised up to 1976 in Reg. B.73 requires joints in cables and bare conductors where necessary to be mechanically and electrically sound. Joints in non-flexible cables shall be accessible for inspection etc...


    Z.



     

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    Farmboy:




    Chris Pearson:

    As for the use of screw terminal as opposed to (MF) junction blocks - are the latter available for greater than 6 mm2 cable; and if so, are the enclosures rated for the current?


    So you may be stuck with traditional junction boxes.




    Are crimps and voltage rated heat shrink not acceptable?


    F


     




    I would consider crimps on a 40 Amp shower circuit cable a "no no." The 4 screw per terminal 60 Amp junction box that I used is much much better.


    Z.

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    AJJewsbury:




    There is a world of difference in a 40 Amp. shower load and a lighting load of a few L.E.D. lamps Andy, as well you know. The possible heating effects are totally different. You are cross threaded. There is no way that the lighting cables could contact the metal light switch plate insulted or uninsulated due to physical separation.



     You never mentioned the the lighting circuit for that metal switch was dedicated to just a few LED fittings 


      

     




    You never asked. Just how may lights would you expect a light switch to operate in a small refurbished flat?


    Z.

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    Have you seen inside one?


    They are probably not a junction boxes as you know them with one screw trying to hold multiple conductors tight in a single terminal, these have individual terminals with two screws for each conductor and cable restraints.


     Andy B.
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    Chris Pearson:




    AJJewsbury:




    I asked the NIC about a screw joint box under fitted carpet and was told that could not reasonably be considered accessible.



    If you asked me, I'd say that if you gained access to the location to install the JB in the first place, it can hardly be regarded as inaccessible. Of course, things might change in the future - being tiled over or covered with glued laminate - but that's a slightly different question.


    I tend to concur. It's a pain in the bottom, especially if the boards are T&G, but isn't lifting boards part of the deal?


    IIRC, there was an article in https://professional-electrician.com by somebody from Wago which argued that under the floorboards is not inaccessible.


    If, however, the sub-floor is sheets of board glued into place, followed by wet under floor heating, and then more boards, perhaps with a decorative or durable finish, nobody is ever going to go through that. Under those circumstances, I have made it clear that should any attention be necessary (presumably not with (MF) equipment) the only way in will be through the ceilings.

     


     




    In this article they nod to the issue of interpretation of accessible but focus on 7671 being vague on definition and basically say what i mentioned that it's differences in judgement but which can be resolved by using MF without resolving the definition themselves - in the article at least - https://professional-electrician.com/features/what-is-accessible-in-bs-7671/

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    Chris Pearson:

    As for the use of screw terminal as opposed to (MF) junction blocks - are the latter available for greater than 6 mm2 cable; and if so, are the enclosures rated for the current?


    So you may be stuck with traditional junction boxes.




    Are crimps and voltage rated heat shrink not acceptable?


    F

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    Sparkingchip:




    Farmboy:




    AJJewsbury:


    Fitted carpets are easily removed...


    ?... a matter of judgement I guess as to what accessible / inaccessible is - a homeowner who doesn't want their fitted carpet pulled up may disagree with you, and it's existence may get lost in the mist of time, particularly if the owner moves, but perhaps a notice at the CU may suffice.


    F


     




    You offer them the alternative, plastic minitrunking run up, across and back down the wall.


    Andy B. 


     




    Or the other alternative, rip the house apart to completely replace the shower circuit, because it’s now half an inch short and the cable was left without any slack.


    Andy B.

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