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Grouping factors on multicore cables

jbrameld
Good afternoon learned colleagues.


Following on from my previous post about the use of 'YY' type cables, our esteemed client has stated that BS7671 does not have grouping factors for multicore cables.  Personally I beg to differ in that table 4C1 states that it is 'rating factors for....a group of circuits or a group of multicore cables....'  What's the hive mind opinion on that statement?


In our case, we have 4 x multicore cables, each carrying 3 circuits each so a total of 12 circuits.  Should we use the figures from the column headed '4' or headed '12'? 12 would give us the worst case, and in fact we are well inside even this figure by our calculations.


Also, the design current for these circuits is only 1.24A, so it is well under the figue of 0.3 x Cg x It at which point under Note 9 arguably all of these circuits could be ignored for grouping purposes anyway.  Do you agree with the vaidity of that argument?


We can park the 'YY' element of the argument for this discussion as the question would equally well apply to the use of a multicore SWA or Harmonised type cable - would you just use the total number of circuits involved from Table 4C1 or is there another method that should be used?


Thanks in advance.


Jason.


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  • 0
    Hi Dave - I may give you a call for a chat - thanks for the offer.


    I think he dug himself a big hole going all-out on the cable type thing - the subject of my earlier post that you helpfully contributed to. The NICEIC audited that installation last week, reviewed all our documentation and passed it accordingly.  Now he has all that information, he's clealry looking for something else to prove that he is 'right' and we are not and/or to make us replace the cabling he doesn't like much.  I enitrely agree with you about the nature of his arguments but am just struggling to get him to shut up and go away (and pay us the money they are witholding....)!


    Slight correction to my OP - each core of each multicore cable is used and wired from an individiual socket outlet on each of 4 lighting bars.  The sockets are paired up at the switch pack so it is a 12 way pack - each way feeding 2 outlets independently wired.  The 24 circuits are split across the 4 cables so 6 circuits in each cable.  Design current for each is indeed based on one LED fixture per circuit so is 0.62A (I originally thought the pairing was done on the bars but it isn't).  So maybe we should apply grouping factors for 24 circuits - table 4C1 doesn't go up that high though....


    With such a low design current, arguably grouping can be disregarded as-per note 9 to 4C1, however whichever way I look at this practically we are so far on the right side of the border that this is all nonsense!


    Thanks again,


    Jason.


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  • 0
    Hi Dave - I may give you a call for a chat - thanks for the offer.


    I think he dug himself a big hole going all-out on the cable type thing - the subject of my earlier post that you helpfully contributed to. The NICEIC audited that installation last week, reviewed all our documentation and passed it accordingly.  Now he has all that information, he's clealry looking for something else to prove that he is 'right' and we are not and/or to make us replace the cabling he doesn't like much.  I enitrely agree with you about the nature of his arguments but am just struggling to get him to shut up and go away (and pay us the money they are witholding....)!


    Slight correction to my OP - each core of each multicore cable is used and wired from an individiual socket outlet on each of 4 lighting bars.  The sockets are paired up at the switch pack so it is a 12 way pack - each way feeding 2 outlets independently wired.  The 24 circuits are split across the 4 cables so 6 circuits in each cable.  Design current for each is indeed based on one LED fixture per circuit so is 0.62A (I originally thought the pairing was done on the bars but it isn't).  So maybe we should apply grouping factors for 24 circuits - table 4C1 doesn't go up that high though....


    With such a low design current, arguably grouping can be disregarded as-per note 9 to 4C1, however whichever way I look at this practically we are so far on the right side of the border that this is all nonsense!


    Thanks again,


    Jason.


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