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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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    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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    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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    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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    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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    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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    I like the idea of crimping on lugs and then soldering them as well. The initial crimping holds the lug and the solder fills any voids afterwards and reduces the possibility of corrosion. . A small hole in the lug allows air to escape when soldering. Lugs were soldered on years ago for connection to bus-bars etc. It is not a good idea to solder on fine stranded wires as they can break due to any vibration in vehicles or vibrating machines though.


    The problem with getting a good reliable crimped connector is that it is just so easy to get it wrong. Limited space work, wrong tools, wrong pressure on the connector, hidden faults etc.

    https://www.youtube.com/watch?v=eedrETFZ3Ws


    Z.
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    Big lug crimping...

    https://www.youtube.com/watch?v=rVT5IsCGNyA


    Z.
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    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.

     





    Then why did I, in my previous role, crimp quite a lot of cables up to 185mm CSA, with the full support of the DNO who had contracted us?

    You are wrong, I think crimps would be the better option compared to screw terminals, which can come loose, however hard you screw them up.


    My current role involves a lot of domestic properties. We have, on average, one shower switch burnt out per week due to loose terminals. I have 2 other very experienced sparkies with me. We all make sure the terminals are as tight as we can get them, yet there are still failures from loose terminals that we know we have tightened properly when we installed them.

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    My current role involves a lot of domestic properties. We have, on average, one shower switch burnt out per week due to loose terminals. I have 2 other very experienced sparkies with me. We all make sure the terminals are as tight as we can get them, yet there are still failures from loose terminals that we know we have tightened properly when we installed them.



     




    So, do you think that the problem is due to the modern single screw shower switch terminals as opposed to twin screw terminals? Or poor manufacture? The vibration of the clunky switch mechanisms, Or another reason? 


    Z.

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    In my experience, there's a WORLD of difference between single indent crimps (commonly used up to 10-16mm2) and a proper, hydraulic hexagonal crimp installed properly.


    However, even with the standard red/blue/yellow plastic cased crimps, if a decent tool is used, and care taken, it works even on solid core wire (a worst case scenario).


    I am surprised nobody has mentioned soldering yet? Is this a dying skill? It really doesn't take very long with a decent setup, and if the joints are well made, it's as good as the original cable.

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