Always been slightly confused on BS7671 for cables before a Meter? 


If as you suggest it will need to meet BS7671, How would Concentric meet BS7671 with CNE after the head?

BS 767 doesn't prohibit CNE any more - it just stipulates a number of conductions (see section 543.4) - which seeing as we don't seem to have any requirement to obtain some Secretary of State's authorization any more, they don't seem too onerous for a supply situation. Alternatively you could use straight concentric with the outer as PE rather than CNE (so needing an extra core, or extra single cable, for N).

Why do you contend Split Con does not meet BS7671, there are millions of meters of it installed in to flats from Ryefields? 


To my mind, its absence of mention does not equal prohibition.

There was a debate a few years ago on the old forum which apparently lead to it's removal from BS 7671 - from memory it was partly that the N part of the armour didn't satisfy the requirement for an earthed armour/sheath for buried/concealed cables - and I think partly that the thin insulation on the N strands wasn't rated for full line voltage - so falling foul of BS 7671 approach of treating N as a live conductor. There's also the issue of providing fault protection to the N conductor - being it's in effect many separately insulated small c.s.a. strands in parallel you'd be looking at an Appendix 10 approach - which can rapidly get very messy (potentially requiring a separate fault protective device at boths ends of each strand).


The DNOs with their assumption of reliable earthing of N conductors (e.g. no switching in N) and more relaxed approach to fault protection, continue to use it of course.


  - Andy.

Always been slightly confused on BS7671 for cables before a Meter? 


If as you suggest it will need to meet BS7671, How would Concentric meet BS7671 with CNE after the head?

BS 767 doesn't prohibit CNE any more - it just stipulates a number of conductions (see section 543.4) - which seeing as we don't seem to have any requirement to obtain some Secretary of State's authorization any more, they don't seem too onerous for a supply situation. Alternatively you could use straight concentric with the outer as PE rather than CNE (so needing an extra core, or extra single cable, for N).

Why do you contend Split Con does not meet BS7671, there are millions of meters of it installed in to flats from Ryefields? 


To my mind, its absence of mention does not equal prohibition.

There was a debate a few years ago on the old forum which apparently lead to it's removal from BS 7671 - from memory it was partly that the N part of the armour didn't satisfy the requirement for an earthed armour/sheath for buried/concealed cables - and I think partly that the thin insulation on the N strands wasn't rated for full line voltage - so falling foul of BS 7671 approach of treating N as a live conductor. There's also the issue of providing fault protection to the N conductor - being it's in effect many separately insulated small c.s.a. strands in parallel you'd be looking at an Appendix 10 approach - which can rapidly get very messy (potentially requiring a separate fault protective device at boths ends of each strand).


The DNOs with their assumption of reliable earthing of N conductors (e.g. no switching in N) and more relaxed approach to fault protection, continue to use it of course.


  - Andy.