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80A BS1361 Time Current Curve

Farmboy
Hi all


Does anyone have a copy of the graph / curve please, either on its own or perhaps along with a 60A curve?


Thanks


F
  • 0
    I have the current curves in an old regs' book. Does this help a bit here?......

    https://www.tlc-direct.co.uk/Book/3.6.3.htm


    Although this might be better that I have just found....

    http://www1.cooperbussmann.com/pdf/f5b2e5d9-2ddd-4332-bbb2-0f03ca7cf10e.pdf


    Z.
  • 0

    Zoomup:

    I have the current curves in an old regs' book. Does this help a bit here?......

    https://www.tlc-direct.co.uk/Book/3.6.3.htm


    Although this might be better that I have just found....

    http://www1.cooperbussmann.com/pdf/f5b2e5d9-2ddd-4332-bbb2-0f03ca7cf10e.pdf


    Z.




    Hi Z


    Thanks for the reply but I'm not sure about the graphs. The graph in the first link only goes up to 60A but I'm after the 80A curve (I already have the 60A curve), and the curves in the second link don't seem to match those in the first (my eyes aren't as good as they were but from what I can see, the time/currents don't seem to match - but I could be wrong).


    Cheers


    F

  • 0

    the curves in the second link don't seem to match those in the first



    Not impossible - manufacturer's data often shows "better" characteristics than the generic data from the fuse's standard or BS 7671 charts. You're free to use manufacturer's data if you want, but it really should be from the manufacturer of the particular fuse you're considering..


    Is this for an EICR or similar? It's just that BS 1361 is now defunct - replaced by BS 88-3 (and 60A by 63A) - and with slightly different time/current characteristics too I suspect.


      - Andy.
  • 0

    Farmboy:




    Zoomup:

    I have the current curves in an old regs' book. Does this help a bit here?......

    https://www.tlc-direct.co.uk/Book/3.6.3.htm


    Although this might be better that I have just found....

    http://www1.cooperbussmann.com/pdf/f5b2e5d9-2ddd-4332-bbb2-0f03ca7cf10e.pdf


    Z.




    Hi Z


    Thanks for the reply but I'm not sure about the graphs. The graph in the first link only goes up to 60A but I'm after the 80A curve (I already have the 60A curve), and the curves in the second link don't seem to match those in the first (my eyes aren't as good as they were but from what I can see, the time/currents don't seem to match - but I could be wrong).


    Cheers


    F


     




    These types of H.R.C. fuses are pretty sluggish in operation and are designed to cope with overloads without the nuisance of fusing too quickly with slight overloads. I have not done so properly, but I will at some point overlay the time/current curves of the B.S. 88-3  fuses over the B.S. 1361 fuses and compare them. I suspect that they are very similar.


    Z.

  • 0

    AJJewsbury:




    the curves in the second link don't seem to match those in the first



    Not impossible - manufacturer's data often shows "better" characteristics than the generic data from the fuse's standard or BS 7671 charts. You're free to use manufacturer's data if you want, but it really should be from the manufacturer of the particular fuse you're considering..


    Is this for an EICR or similar? It's just that BS 1361 is now defunct - replaced by BS 88-3 (and 60A by 63A) - and with slightly different time/current characteristics too I suspect.


      - Andy.

     




    Looking at adding a socket in a domestic installation that has an 80 1361 main fuse. I'm replacing the 10mm2 earthing conductor with 16mm2 but just for giggles thought I'd give the adiabatic a spin.


    F

  • 0

    but just for giggles thought I'd give the adiabatic a spin.



    Provided Ze is reasonably low it'll likely be more than adequate - I think I remember one case here of a 2.5mm² earthing conductor on a TN-S system and it was shown to comply! Nevertheless a good exercise to do!


    I think Mike might have posted what you want on the old Forum: https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=64556 in his post of  14 March 2016 09:08 AM.


      - Andy.
  • 0
    I assume that you have now done the calculation farmboy and realised you don't have to change the Earth conductor. You can use the old figures for a BS1361 fuse and you will see you are very safe unless the PSSC is very low, in which case you may need to fit an overall RCD to get a reasonable trip time in case of a short circuit (which is very unlikely on the tails if they are fitted properly). The main cutout fuse is for overall maximum demand protection, protecting the service cable rather more than in case of a short circuit, but it does that as well providing the PSSC is high enough. Some rural supplies have PSSCs in terms of less than 200A, so fusing times can be very long even with a direct short, then the main earth cable could get somewhat warm, but nowhere close to failure.
  • 0

    AJJewsbury:




    but just for giggles thought I'd give the adiabatic a spin.



    Provided Ze is reasonably low it'll likely be more than adequate - I think I remember one case here of a 2.5mm² earthing conductor on a TN-S system and it was shown to comply! Nevertheless a good exercise to do!


    I think Mike might have posted what you want on the old Forum: https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=64556 in his post of  14 March 2016 09:08 AM.


      - Andy.

     




    Thanks for this Andy and Mike, much appreciated.


    F

  • 0

    davezawadi:

    I assume that you have now done the calculation farmboy and realised you don't have to change the Earth conductor. You can use the old figures for a BS1361 fuse and you will see you are very safe unless the PSSC is very low, in which case you may need to fit an overall RCD to get a reasonable trip time in case of a short circuit (which is very unlikely on the tails if they are fitted properly). The main cutout fuse is for overall maximum demand protection, protecting the service cable rather more than in case of a short circuit, but it does that as well providing the PSSC is high enough. Some rural supplies have PSSCs in terms of less than 200A, so fusing times can be very long even with a direct short, then the main earth cable could get somewhat warm, but nowhere close to failure.




    ... in which case you may need to fit an overall RCD to get a reasonable trip time in case of a short circuit (which is very unlikely on the tails if they are fitted properly)...


    Sorry if I'm being dense but just checking my understanding of what you're referring to here. An RCD won't trip on short circuit, will it, so did you mean earth fault current?


    F

  • 0
    Only shorts via earth affect the rating of the earth conductor, which is what I think you are  sizing adiabatically in this example.


    Also L-N faults have no upper limit to the breaking time, except that set by cable failure.

    L-E faults need to be off in half a heart beat for very good safety of life reasons.

    DZ is reminding us to look also  at the extreme high Zs case, where an L-E short does pull up the earth voltage to near live but does not draw enough current to blow the supply fuse in any usefully short time. The opposite case to the adiabatic how where the limit is "how hot is my cable for a dead short close by the Xformer ? "

    300mA RCD 1/3 second delay or 100ma 1/10 second delay at the origin usually fixes.


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