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Cable type to use

Hi,

A relatively minor issue but your thoughts will be appreciated.

An existing domestic installation is to have the internal service head moved to a new external meter box. A new 10m long 80-100A 1ph distribution cct will therefore be run from a switch fuse in the meter box (contentious, perhaps) to the CU.

The meter box will be approx 2-3 feet off the ground. The proposed cable route is to drill through the wall below the meter box up to approx a foot of the ground, that will go through into the basement.

The distr cct will be in the order of a 25mm2 cable. The issue is then the type of cable to use?

- A 3 core SWA will be difficult to use because its bending radius will be too great to get into the meter box; and drilling downwards to lessen the angle is inadvisable given water could track down the cable into the basement even after packing with sealant but which may deteriorate.

- Tails could be used, that are mechanically protected in e.g. conduit emanating from an adaptable box.

- Of interest though (due to not having used it before) is thoughts on using split-concentric in this scenario (which table F5 of GN 1 lists for general use) - given the short distance between the hole and the bottom of the box, perhaps it will be easier to bend up into box.

So thoughts please on using split-concentric.

Thanks.

Parents
  • 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?

Reply
  • 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?

Children
  • 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.