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Armour bonding: Effect on cable rating

Hi all,

Inspired by this recent post (but not wanting to digress too far), the advantage of single-bonding cable is ostensibly the reduced circulating current in the armour and hence increased capacity in the line conductors... But can anyone tell me if there’s a way to quantify this benefit, without recalculating on first principles per IEC60287? Is it as “simple” as calculating the induced voltage using the method in the IET calculations book and then “adding back” the avoided current that would have otherwise ensued to the tabulating rating?

Also I most commonly see this applied at private transformer tails... but surely there they’re normally so short it’s of little benefit unless you’re mainly concerned with fault current rating?

Thanks as always.
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  • My recollection is that for single point bonded armoured cables you can use the ratings for the unarmoured version of the same cable.

    The extra layer of plastic adds a bit to the thermal resistance and the greater diameter adds more surface area so the two effects nearly cancel out.
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  • My recollection is that for single point bonded armoured cables you can use the ratings for the unarmoured version of the same cable.

    The extra layer of plastic adds a bit to the thermal resistance and the greater diameter adds more surface area so the two effects nearly cancel out.
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