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Cable grouping factor - Space on ladder for no groupping

Apostolos
Good morning everyone.

If I may ask the more experienced members here...

I have a ladder with various submains departing from a Main Switchboard.

Is there any distance I could leave between a specific submain cable and the rest of the cables on the ladder (left and right) that allows me to get away from any grouping factor for this specific cable?

For example something like twice the external diameter of the cable left and right of the cable?

(Just an example)

Thanks
  • Former Community Member
    0 Former Community Member
    See note 2 to table 4C1 - essentially, when the cable horizontal clearance is at least 2 x the cable effective diameter, then no grouping factor need be applied.


    You need to be certain the contractor can achieve that, before you specify the cable size - they won't like very much for specifying spacing, either ? - contractor preference is to lump the lot on together with lots of random plastic ty wraps rather than cleat cables to achieve desired spacing !!


    Regards


    OMS
  • 0
    OMS.....I AM the contractor ??

    Now....people on site probably will not send me a Christmas card but....whatever!
  • Former Community Member
    0 Former Community Member
    LoL - I'm so sorry to hear that, but chin up, eh - hopefully things will get better for you


    Just keep saying "spaced a minimum of 2 x De, please" - you might get through


    OMS
  • 0
    The ladder is only 3 meters in legth so they will manage to keep the distances....I hope....
  • 0
    Indeed - you are aiming for un obstructed airflow on either side of the cable, so it may as well be more or less in free air.

    The grouping factors assume all the other cables are running full load too, it may be that if the main supply is limited to less than the full load of all the other cables, (actually that is quite common),  so the worst case  cannot occur, so it may not be as bad as the simple rules suggest.

    Be aware that side by side spacing is better cooled than vertical, as the rising hot air from the lower cables will heat those above. It gets a lot better than the tables suggest if there is a steady draught  to replace the hot air with cold, and much better again (only if the cable is a type that can stand it) with water or oil cooling.  So to space things out for heat problems in tight places, to add some extra ladder basket or tray beside on unistrut or outriggers is better from a cooling perspective, although worse from every other point of view, than adding a second one above or below.
  • 0
    The problem was in a few words the following:

    DNO ACB in one corner of plant room

    Main switchboard in the other corner of plant room

    Ladder in between for parallel singles 150mm2 XLPE/LSF

    The problem is that people on site decided to use this ladder for the outgoing submains of the switch panel which means that my calculations for the incomer would be ruinned by a grouping factor that I initially had not predicted.

    Now I am trying to push the incoming tails on one side of the ladder and the outgoing circuits on the other side of the ladder spacing them so that one does not affect the other.

    If this does not succeed I will ask them to install a second ladder 30cm above this one for the outgoing circuits keeping this ladder only for the incoming tails

    Cheers

  • 0
    Ah  - ingoing and outgoing will be both loaded at once of course.  sounds like you have a plan though.

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