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ducting under concrete floor

Former Community Member
Former Community Member
hi 

so im trying to work out current carrying capacity for cables running through a 4m length of 50mm duct there are 4 circuits one at 40A 2 at 32a and one at 20a all in twin and earth what reface method would people use as its not armoured can I still use method D also for what I can see derating for cg would be 0.5 which would mean the 40A being run on 16mm which sounds crazy
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    Reference method B would be the one to use. Take the actual cable loading into account, rather than the maximum (looks like a cooker, some sockets and a fixed appliance to me), so diversity may also be applied. It looks like 1 10mm (50A), 2 4mm (Ring 28A), and 1 2.5mm would suit, but you may care to make the ring a radial, then you need 1 10mm (50A), 1 6mm (36A) 1 4mm(28A). Concrete is quite thermally conductive, but the above would not be right if you have underfloor heating, 1 size larger for each should suit. I have used the more conservative 3 phase numbers, but this is a bit of overdesign which makes no difference in reality.


    Regards

    David

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