Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 6 replies
  • Subscribers 32 subscribers
  • Views 3710 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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


Parents
  • 0
    You need to be careful with split concentric. As others have said, it should be regarded as offering the same protection as twin & earth from BS7671’s point of view. The earthing copper “armours” cover about 2/3 of the diameter of the cable, with the neutral and a couple of separators covering the remaining diameter. DNO’s regulations allow the neutral to be treated as the same voltage as earth, BS7671 calls it a live conductor. It does not qualify as meter tails, as the conductors are not double insulated and should be protected by a customer-owned fuse as you would with an SWA submain. In fact, in some cables the thickness of the neutral insulation means it is “covered” for identification, not “insulated”. 


    Regards,


    Alan.
Reply
  • 0
    You need to be careful with split concentric. As others have said, it should be regarded as offering the same protection as twin & earth from BS7671’s point of view. The earthing copper “armours” cover about 2/3 of the diameter of the cable, with the neutral and a couple of separators covering the remaining diameter. DNO’s regulations allow the neutral to be treated as the same voltage as earth, BS7671 calls it a live conductor. It does not qualify as meter tails, as the conductors are not double insulated and should be protected by a customer-owned fuse as you would with an SWA submain. In fact, in some cables the thickness of the neutral insulation means it is “covered” for identification, not “insulated”. 


    Regards,


    Alan.
Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines