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What would the group rating factor be for more than one layer of many multicore cables laid on a cable ladder system?

Okechukwu Ezeaba

Considering many distribution circuits where many multicore cables would be on laid on a cable ladder system all touching with more than one layer, what will the group rating factor be? As per Table 4C4 of BS 7671, I observed that values were given for just single layer of cables up to 9 cables. Please note that some of the cables would be used for intermittent loads and they are not all of the same sizes.

  • +1

    My guess would be that once you bunch many cables together in many layers the most significant factor in restricting heat loss will be the other cables, and the means of support will matter much less - so maybe go down the table 4C1 (item 1) route.  Although I suspect the low factors that yields might suggest that bunching many power cables together isn't an ideal solution anyway.

        - Andy.

  • 0

      I too seem to have disappearing replies ....

    did I type something wrong?

        - Andy.

  • 0

    If you're happy to step out of the BS7671 multiplicative rating factor approach ERA 69-30 pt VII might be worth a look, albeit it's a time consuming method, but I agree that such a bunch is probably not the best solution for power circuits.

  • 0

    What about table 4C1 item 1?

  • 0 in reply to AJJewsbury

    Okay, thank you for that suggestion.

  • 0 in reply to Jam

    Thank you Jam

  • 0 in reply to AJJewsbury

    No  , seems that our auto moderation system had a tizz and put your reply in the queue for review? Strange that it was noting your reply but not displaying it though! Will investigate further so please do contact me if it happens again (with screenshots) either via PM or via community-online@ietengx.org 

  • 0

    Really you need airflow - the whole point of a basket, ladder or well perforated tray is that air can circulate between the cables. As soon as you prevent that, or one cable is being heated by the hot air from the layer beneath, you lose most of the advantage and you may as well just screw the cables direct to the wall, or ceiling or whatever. Of course if the cables are sized for volt drop reasons, rather than load, and are not running near full load, then layers are fine.

    but yes, treat as a bundle of cables.

    Mike.

  • 0 in reply to Stuart Urban

    Thank you Stuart

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