chasing cables/ sinking back boxes

[Staffbull]

Just started chasing the cable runs and sinking back boxes with SDS box sinker and wheel chaser. (works a treat) howver the blocks are GP1's (4" hollow) so when I sink the boxes I'm left with a deeper hole than required due to the cavity in the block, do I simply pack back out with sand/cement? and also is it OK to "glue" the galvenised back boxes into place or do they require a mechanical fixing. I'd prefer to glue them as drilling and fixing to the sand and cement would not hold very well I would have thought.

Cheers

[John White]

I'd glue them in with something like this:

in the case of a big hole, this:

[Staffbull]

cheers John, I wont have the problem with most of the boxes as i've got

25mm deep ones for the double sockets and I'll need 13-15mm for the cement first coat and pink proud of the block surface so will only need to go in 10mm.

is there a minimum depth for the cables to be channled? and would this be from the finished surface (i.e can I count the plastering as part of the cable depth) I have 2" PVC channel to go on top of the chases

[John White]

Assuming the cables are in the permitted zones, then they only need to be deep enough for the plasterer to get a 3 to 5 mm (1/8 to 1/4 inch) covering over the channel. Anything less often leads to cracking as the plaster dries out.

If the cables are outside the zones then they need to either be 50 mm (2 inches) below the surface, or mechanically protected.

John

[Staffbull]

Cheers John, by zones i take it horizontal or vetrical in line with the visible outlet If so then they are all in. Also what is the permissable distance I can put a socket near a sink in the kitchen?

[John White]

See:

If so then they are all in. Also what is the permissable distance I

This is one of those questions to which there is no definitive answer. The usual answer is either 305 mm (12 inches) or where they won't get splashed.

John

[Staffbull]

Cheers for the link, all cable runs comply !! I was under the impression I could not fit a socket in a location where I could touch the sink and the socket at the same time, which prevents me putting one where I would like. It will be a metre away so not likley to get splashed :-)

another issue I have is that some of the cables for the sockets need to come down through a joist next to the wall, but the holes would fall less than the permissable 0.25-0.40 zones for drilling holes. Bloody regs are starting to grate !! the holes would only be big enough for

2.5mm to fit through so hardly a threat to the structure !! any ideas?

Thanks in advance

[Owain]

In most houses that would prevent putting any sockets in the kitchenette.

I don't quite understand where the joist is (parallel or across the wall) but remember at the top ty millimetres of wall is a permitted zone too, so you can do a little wiggle horizontally.

Owain

[Staffbull]

Hi the joist runs with the wall and is flush with it ( not at 90) and I need to run several runs of 2.5 down that wall as this will be the main kitchen wall and will have 4 dbl sockets on it. the only option I can see to stay in regs is to run the cables to that wall through a hole in the permissable drilling zones and into the

150mm top "zone" and use that to take the cables to their sockets. Would be 10 times easier to drill a 10mm hole in each location of the joist, 10mm out of 195mm joist isnt going to weaken it significantly

[Owain]

Is this a top floor/single storey? IOW, is the joist supporting any weight or is it in tension preventing a pitched roof from splaying?

Either way, if the joist is supported by the wall it's unlikely to deflect, and without deflection drilling a few holes shouldn't weaken it sufficiently for it to give way.

But IANAStructuralEngineer and I haven't seen your house.

Owain

[David Hansen]

On 19 Sep 2006 10:42:26 -0700 someone who may be "Staffbull" wrote this:-

You should only need to run two 2.5mm2 cables down the wall, one at the "start" of the run of sockets and one at the "end". Cable can run horizontally between the sockets.

[Staffbull]

Hi Owain, its the fist floor of a two storey extension. BCO coming today to give me guidance

[Staffbull]

in that wall as well, as its by far the "buisyest" wall reagds chasing sinking I thought I'd start on that first, the rest should then be "plain sailing"

[David Hansen]

On 20 Sep 2006 02:00:31 -0700 someone who may be "Staffbull" wrote this:-

Presumably not 2.5mm2. Do you need separate feeds because you are controlling them from a central point, or just one permanently live feed to local switches? If the former could you use three core and earth, or some combination of cables if you have lots of the lights?

Presumably more than 2.5mm2.

[Staffbull]

run off the same junction box as a twin flourescent and two FCU's