Split concentric is often used and should prove satisfactory in service. Two caveats though, firstly all live conductors, including the neutral, now require double insulation. The neutral wires in split concentric are "covered" rather than "insulated"  Secondly, the larger sizes of split concentric including 25mm generally have a solid aluminium core. Are you certain that the terminals at BOTH ends are suited to aluminium conductors ? Many are for copper only. The solid aluminium conductor is also less flexible than the stranded copper formerly used.

Assuming CEF are not mistaken in their advertising, they have 25mm copper core split con, and by the look of it will sell a short length.

https://www.cef.co.uk/catalogue/products/2326534-25mm-split-concentric-cable-cut-length-sold-by-the-mtr

Maybe worth buying a length as a sample to offer up.  Otherwise presumably it is ducting and singles.

Mike.

Can someone clarify about split concentric please. I`ve heard it said that we are not allowed to use split concentric.

The reason, armoured cable must have all live conductors surrounded by an earth armour. Split con uses earth and also N for "armour".

N is a Live conductor just the same as phase (or line) is. We are not allowed to use N as an armour.

You cannot meet BS7671 and use split con  in any situation where you should be  relying on earthed armour for protection - shallow buried in walls not following lines of least surprise, burial in places where it might be damaged unless in some suitably strong and obvious  duct etc, you need the armour,

However, on the surface, so the route is visible or buried anywhere you might safely route or bury a non armoured cable  - and I agree that needs careful thought- you are OK, and rather like  this use of 5 core NYYJ  I mentioned a few weeks ago, it will always be unusual.

Mike.

So not barred as such in itself. Say you might use where you`d use clipped T & E for example but not where armouring is required. So not an everyday substitute for SWA like some seem to think it is?

In so far as BS7671 is concerned. DNO have their own usages and rules of all sorts of things that might be alien in BS7671 land.

If the situation is such that split-con is acceptable, then you might as well use insulated & sheathed singles - likely to be much easier to work with.

   - Andy.

except perhaps for UV resistance - you may or may not  be happy running  meter tails clipped direct or in mini trunking up the outside of a building,but I'd be happier with split con.

The DNO's rules consider neutral conductors to be 'at or near' earth potential, rather than 'live' and the same risk as a phase conductor would be in the way that BS7671 does.

Of course in real life the live neutral reversal thing is not commonly an issue, being more of a third fault to danger,  and so the split con is far less likely to expose a dangerous live and not operate the ADS, than a sheathed single  if it does get  mechanically damaged in some way. Neither may be a good choice in the '7671 view, but split con is perhaps a rather less serious non -compliance.
Mike

Thank you for the replies everyone.

Mapj1 - I'd mentioned that I was considering putting an AB over the hole in the wall (with a PVC conduit liner in the hole in the wall) with a conduit then running up to the underside of the meter box, so enclosing/protecting the Flexi-tails/protective conductor contained therein (the cables then being clipped direct to the joists in the basement) - so do you not like that as an option?

No its fine - in that case I think the risk of mechanical damage, or exposure to the elements is managed to a sensible level somewhere between ' most unlikley' and 'improbable'.  The space under the meter box will not suffer heavy abuse, and if it does you have other problems. My comment was a more general one about what to think about if making the choice.

sorry if that was not clear.

M

Thank you for your prompt reply, it is much appreciated.

T.