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Split concentric ccc?

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 David Stone over 5 years ago

Whilst this case is somewhat unusual, and not compliant with several regs. it is not dangerous in the usual meaning of that and should probably only get a comment as Mike says. Remember that a nail or screw (the usual danger cited) would need to travel through the N conductor strands to contact the potentially dangerous live conductor. This would probably blow the DNO cutout fuse without any difficulty. You should be aware that 522.6 applies to walls and partitions, and this floor is not a partition, so slightly sticky anyway. The requirement for Fusing tails of more than 3 metres is a DNO one not BS7671, so just an observation. Split concentric is not a specified cable type either, but again not a cause of danger, just difficult to terminate.

The outcome of this is that you should note the deviation from BS7671 but not code it. In my view as described it is not a danger, or potential danger. You do need to watch the letter of the regs. too, the actual words may not be those one expects!
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0 David Stone over 5 years ago

Whilst this case is somewhat unusual, and not compliant with several regs. it is not dangerous in the usual meaning of that and should probably only get a comment as Mike says. Remember that a nail or screw (the usual danger cited) would need to travel through the N conductor strands to contact the potentially dangerous live conductor. This would probably blow the DNO cutout fuse without any difficulty. You should be aware that 522.6 applies to walls and partitions, and this floor is not a partition, so slightly sticky anyway. The requirement for Fusing tails of more than 3 metres is a DNO one not BS7671, so just an observation. Split concentric is not a specified cable type either, but again not a cause of danger, just difficult to terminate.

The outcome of this is that you should note the deviation from BS7671 but not code it. In my view as described it is not a danger, or potential danger. You do need to watch the letter of the regs. too, the actual words may not be those one expects!
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Split concentric ccc?

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