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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
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  • 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.
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  • 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.
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