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Split concentric ccc?

Farmboy

Hi all



Basically, what ccc table, if any, in apdx 4 would be used for split concentric? I've had a look on the old forum but couldn't see a definitive answer, so sorry if I've just missed it.



The scenario is an existing domestic installation has an approx 7 metre run of what appears to be 25mm2 cable running from the external meter box, under the floor, to the internal CU, on a 100A main fuse, with no switch fuse.



The installation method is awkward to determine because the cable comes up internally through the floor screed, making it seem to be buried under the concrete floor. However, there also appears to be an approx rough/faint 100mm circular pattern around the cable which makes me think there may be a duct (probably brown plastic drainage pipe) just below the surface, but can't be sure, could just be the way the screed was smoothed around the cable.



So, if there's a duct, will that satisfy reg 522.8.10 (probably no cable making though), so the concentric can remain? But if there's no duct, should it be disused/replaced because the cables protective earth only surrounds 1/3 of the cable?



So if the cable can remain, what ccc and size of switch fuse?



Thoughts please - apart from run the other way ?


F


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  • 0
    Assuming it is this stuff  see the table of current ratings  on page 2.  No more than an odd % or two different to the SWA figures. for the same copper cross section.

    As you say it is not one of the cable types already listed in the regs, so some professional judgement is needed, but if in doubt, makers figures are always the trump card.

    If it is indeed 25mm sq, then a 100A fuse will be safe.

    Because the earth is not a full all-round armour like SWA, then the regs do not consider it to be any safer than twin and earth or any other non-armoured cable in terms of recommended routes, so needs to be 50mm or deeper, or obvious , or in conduit/trunking etc 

    Or of course a note that compliance to current regs cannot be verified..
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  • 0
    Assuming it is this stuff  see the table of current ratings  on page 2.  No more than an odd % or two different to the SWA figures. for the same copper cross section.

    As you say it is not one of the cable types already listed in the regs, so some professional judgement is needed, but if in doubt, makers figures are always the trump card.

    If it is indeed 25mm sq, then a 100A fuse will be safe.

    Because the earth is not a full all-round armour like SWA, then the regs do not consider it to be any safer than twin and earth or any other non-armoured cable in terms of recommended routes, so needs to be 50mm or deeper, or obvious , or in conduit/trunking etc 

    Or of course a note that compliance to current regs cannot be verified..
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