Channeling the wall for 2.5mm cable

phykell · 9 Dec 2004

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...

ban-all-sheds · 9 Dec 2004

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....

dw3101 · 9 Dec 2004

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!!!

phykell · 9 Dec 2004

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!

andy · 9 Dec 2004

phykell said:
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.

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

dw3101 · 9 Dec 2004

dont use the grinder as a first choice..

JerryD · 9 Dec 2004

or even as a second choice

phykell · 9 Dec 2004

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.

It's not exactly a channeling tool like this one:

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

jonob · 9 Dec 2004

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

andy · 9 Dec 2004

phykell said:
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. It's not exactly a channeling tool like this one:

http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=18393&id=16606[/QUOTE]

i just use a 30mm chisel.

to do it this way, have it at a slight angle to the wall, start hammerin and move the chisel up or down. do for each side and try and go deep then a few hits and the centre usually comes fallin

ban-all-sheds · 10 Dec 2004

jonob said:
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

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.

phykell · 10 Dec 2004

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?

Damocles · 11 Dec 2004

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.

dingbat · 11 Dec 2004

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.

jonob · 11 Dec 2004

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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Channeling the wall for 2.5mm cable

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