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Terminating Twin and Earth

nicemark
I have been arguing about the methods of separating out the ends of twin and earth cable.


An old accepted trade method was to simply grip the earth wire and tear it out of the insulation to split the ends open.

However this puts considerable strain on the earth wire and in the case of 1mm wire it is very easy to stretch a significant amount. 


I was wondering if you there is data or evidence to demonstrate that this method is not acceptable. 

  • Former Community Member
    0 Former Community Member
    Was taught to  up n pull back one of the line conductors, also not to bend the stripped ends when terminating. 

    regards ts
  • 0
    I think at some point you would notice if one of the cores was a different length after stripping back.  



    Gary
  • 0





    1928 Posts






     



     





    I agree with this method. During my time as a college lecturer, I occasionally helped with Wiring and Regulations classes and this is the method we taught students. An alternative is to snip down both sides of the cable with the pliers and pull on the insulated conductors, but less easy. We discouraged the usage of knives for the reasons given.


    Another reason,  probably the main reason, for putting sleeving on the earthing conductor is to avoid a chance contact with another terminal. I once came across a case where this had happened on a socket outlet. The uninsulated earthing conductor had snagged the live terminal and was completely fractured in the ensuing flash, leaving the portion connected to the earth outlet welded to the live terminal - nasty!
  • 0
    Hi Mike

    Thanks for that reply. Though I have not used scales, your figures seem much more like real life than others I have been quoted. Furthermore the 28KG to snap it (gently applied) seems true. I have used much less force than that to considerably stretch 1mm wire. 

    So this confirms my theory, so now I am puzzled as to why stressing the CPC has not been made an issue before, particularly on the small CPC sizes.

    Nice pliers too.
  • 0
    It is not an issue, that is why! The micrometer reading tells one that at once. There is one cable type where the "cheesewire" is not good and that LSF T&E. The sheath is very much stronger and also has a high tensile strength. The 8 shaped stuff is particularly difficult, I resort to a cable knife.
  • 0
    so now I am puzzled as to why stressing the CPC has not been made an issue before, particularly on the small CPC sizes.

     


    The C.P.C. is strong enough to cheese cut through the outer P.V.C. sheathing of smaller twin and earth cables at room temperature, or slightly below, because the sheathing is thinner and more easily cut than with larger cables. Anyway, the 1.5mm2 C.P.C. and above of larger cables make good cheese cutters once the end of the cable has been cut slightly and the cut started. No problem.


    Z.


  • 0
    Zoomup:

     Anyway, the 1.5mm2 C.P.C. and above of larger cables make good cheese cutters once the end of the cable has been cut slightly and the cut started. No problem.

    .




    But the issue isn't whether the cpc is effective as a cheese cutter; it's whether the act of bending then straightening each bit of the cpc under pressure in some way damages it - e.g by work-hardening it and/or stretching it etc.


  • 0
    wallywombat:
    Zoomup:

     Anyway, the 1.5mm2 C.P.C. and above of larger cables make good cheese cutters once the end of the cable has been cut slightly and the cut started. No problem.

    .




    But the issue isn't whether the cpc is effective as a cheese cutter; it's whether the act of bending then straightening each bit of the cpc under pressure in some way damages it - e.g by work-hardening it and/or stretching it etc.




    Yes I understand your concerns. The C.P.C. is strong enough to be used as a cheese cutter  in my experience and does not work harden. Any copper conductor can be bent several times during termination. I have not noticed any work hardening during these types of operation. The biggest danger is nicking a copper conductor, where then afterwards , it is likely to easily break clean through, especially 1.0mm2 sized copper conductors.


    Z.


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