running mains cable underfloor along a concrete sub floor

[officer dibble]

I have just had an extension built to extend the kitchen and provide another room.The old kitchen area has honeycomb walls supporting a floor joists on a concrete base. The base is clean and without debris. The builder has suggested that when the electrician comes to to wire it up he could pass the cables along the void between the concrete base and the floorboards to the new extension and that they could lay on the base without being clipped to the joists. I would therefore avoid the need to have the the kitchen cupboards and flooring removed. Is it ok to do this as far as regulations are concerned, ie to have the cables trailing along the concrete sub base between the sleeper walls?

 

[telectrix]

as long as the cables will not be subjected to any possible damage, then OK. or clip to joists where possible.

 

[Midwest]

I think you should let the electrician decide where to run the cables for you extention, not the builder; isn't it a bit late now?

What is the depth of the void between the concrete slab and the top of the wooden joist?

BS7671, reg 522.6.101-103 i.e. a cable installed under a floor or above a ceiling shall be run in such a position that it is not liable to be damaged by contact with the floor or the ceiling or their fixings......It goes on to give numerous conditions, 50mm space, metallic coverings, RCD protection etc.
Part A Building regs, covers notches in floor and ceiling joists and Part P 2.3.2 states unamoured cables should be at least 50mm from top or bottom of a joist.

At some point I suspect your cables may need to cross a joist at right angles, which may be less than 50mm and could weaken the floor structure?

 

[keniff]

I have got to admit iv run untold amount of cables under floorboards with rods so they are just laying on the ceiling no 50mm there! Sometimes it's just not possible to clip to joist

 

[Midwest]

Suppose that's okay with RCD or some form of mechanical protection, I've done the same in the past. But weakening the joist is not acceptable, is it?

 

[officer dibble]

I think you should let the electrician decide where to run the cables for you extention, not the builder; isn't it a bit late now?

What is the depth of the void between the concrete slab and the top of the wooden joist?

BS7671, reg 522.6.101-103 i.e. a cable installed under a floor or above a ceiling shall be run in such a position that it is not liable to be damaged by contact with the floor or the ceiling or their fixings......It goes on to give numerous conditions, 50mm space, metallic coverings, RCD protection etc.
Part A Building regs, covers notches in floor and ceiling joists and Part P 2.3.2 states unamoured cables should be at least 50mm from top or bottom of a joist.

At some point I suspect your cables may need to cross a joist at right angles, which may be less than 50mm and could weaken the floor structure?

The area in question is not in the new extension but in the original house, the cables will be lying loose on the concrete base slab about a foot under the floorboards put there using a rod.

 

[mark80]

Get the electrician out to advise incase the builder is talking crap and causes you problems. At the end of the day, you wouldn't take advice off an electrician on how the extension should be built would you?