Channeling the wall for 2.5mm cable

Discussion in 'Electrics UK' started by phykell, 9 Dec 2004.

  1. phykell

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    Hi,

    I'm doing a few channels in plastered breeze block. I've got an SDS drill/breaker, a channeling tool and an angle grinder, plus I've hired a square hole cutter for the socket boxes. If I'm about to cut the channels for a ring-main circuit, what width/depth would you recommend? I assume that I need enough for the two cables to be cable clipped side-by-side and then for some PVC cladding to be placed over them? So this would mean that the channel width only has to accomodate the cladding's width, but what cladding would I then use to cover a pair of 2.5mm cables?

    I'm sure I asked a similar question before and got an answer, but having searched through all my previous posts, I can't find anything... :confused:
     
  2. ban-all-sheds

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    1) Are you prepared for the monumental mess that those tools will make when applied to a breezeblock wall?

    2) Why two cables side by side?

    3) If you've got freedom of choice regarding channel width & depth, don't clip the cables and cap them - run them through oval PVC conduit....
     
  3. dw3101

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    as deep as posible inho.. I like to allow at least 10mm between top of cable and the surface.

    You are going to make such a mess!!! :D :D
     
  4. phykell

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    The square hole cutting tool is a fantastic bit of kit! Just fitted 6 back boxes in less than 2 hours. Sure you electricians might laugh but these boxes usually have me pulling my hair out and taking hours to get them right. Best of all, the boxes are level and the amount of material removed around the boxes is minimal.

    The oval conduit sounds OK, but I've already got the clips and the capping. I might take a trip to B&Q later though now you've suggested that...

    As for the mess, yup it's really bad, and I haven't even started with the angle grinder yet! :D
     
  5. andy

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    use the SDS for all the chasing. not as much mess as the angle grinder
     
  6. dw3101

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    dont use the grinder as a first choice..
     
  7. JerryD

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    or even as a second choice
     
  8. phykell

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    :D I think I'm getting the point hammered (no pun intended) home!

    So don't use the angle grinder then :)

    I have an SDS chisel set which includes a gouge chisel. I'll give that a go but I seem to remember having difficulty with it for some reason. :confused: It's not exactly a channeling tool like this one:

    http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=18393&id=16606
     
  9. jonob

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    you dont need to cover cable with capping if the runs are either vertical or horizontal

    only cover if the run is diagonal or any route not mentioned above :D
     
  10. andy

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  11. ban-all-sheds

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    Here we go again with that old half-informed nonsense.

    Regulation 522-06-06
    A cable concealed in a wall or partition at a depth of less than
    50 mm from the surfaces of the wall or partition shall:
    (i) incorporate an earthed metallic covering which complies with
    the requirements of these Regulations for a protective
    conductor of the circuit concerned
    , the cable complying with
    BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or
    BS 8436, or
    (ii) be of insulated concentric construction complying with
    BS 4553-1, BS 4553-2, or BS 4553-3, or
    (iii) be enclosed in earthed conduit, trunking or ducting satisfying
    the requirements of these Regulations for a protective
    conductor
    , or be mechanically protected sufficient to prevent
    penetration of the cable by nails, screws and the like
    , or
    (iv) be installed in a zone within 150 mm from the top of the
    wall or partition or within 150 mm of an angle formed by two
    adjoining walls or partitions. Where the cable is connected to
    a point, accessory or switchgear on any surface of the wall or
    partition, the cable may be installed in a zone either
    horizontally or vertically, to the point, accessory or switchgear.
    Where the location of the accessory, point or switchgear can
    be determined from the reverse side, a zone formed on one
    side of a wall of 100 mm thickness or less or partition of
    100 mm thickness or less extends to the reverse side.

    So basically if the cable is not in one of the acceptable zones and it is not more than 50mm deep, it needs protection, and capping does not provide protection.
     
  12. phykell

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    Interesting. So if I want to bed cable in my wall, I need to use metal capping, is that right? I'm sure I've seen it, perhaps in B&Q but I can't find anything suitable on Screwfix or ToolStation. Surely by what the regulations say then, I can't even use oval PVC conduit?

    Thinking about it, a picture would be nice. Has anyone got a picture of a suitably protected pair of 2.5mm T&E cable for a ring main socket, embedded in a wall?
     
  13. Damocles

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    Most people run cable vertically or horizontally from a fitting of some sort. Then it comes into section iv above, and no protection is required at all. You can just tack it in place and bury it in plaster if you want, but if you use either capping or conduit then the tunnel allows it to be replaced or adjusted in the future.

    You can also run it on the surface anywhere you want.
     
  14. dingbat

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    Just to reinforce the advice from Dam and B-a-s:

    If you are going to cap the cable, don't clip it. Run the cables, without twisting, side by side and cover with a suitable section of galvanised capping, fixed with galvanised clout nails. Ideally you should turn over any sharp ends before fixing. If you do this with the capping running all the way from box to ceiling/floor, you should create a channel which will allow you some movement of the cables. It can be tricky the first few times, but it's far better than clipping and protects the cable during plastering.

    At the free end, whether in the ceiling or floor, leave yourself a short loop of cable running directly into the top/bottom of the channel (i.e. not bent over) so that, if you make a mess of terminating in the socket you can pull in a little spare. If you embed them directly in plaster you won't be able to do this.
     
  15. jonob

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    sorry what i meant when i said not to cap if horizontal or vertical

    was not to cap if horizontal or vertical between and accesory or a cu

    sorry hope its clear now

    reg 522-06-06
     

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