Wiring in concrete floor

[alistairmonkey]

Hi,

we need a ring circuit in our living room, currently there is only 1 socket direct from the consumer unit. It is a concrete floor which we're going to put a solid wood floor on to, the walls are quite flakey but are going to be skimmed. It's quite a small room and will have about 5 double sockets.

Where's the best place to put the wiring ? Is it ok to chase a channel in the floor and run the cable in there ? Does it need to be in earthed metal conduit or are there other options ? Just out of interest, are there any regs about where such a channel can run (i.e. distance from wall etc) ?

Sorry for all the questions, i'm trying to guage how much of this job can be done by myself

Thanks
Alistair

 

[Chri5]

If you are putting a solid wood floor down why not go fixed rather than floating the floor ?

Battons on the concrete and nail the flooring to the battons, this then gives you a good space under the floor to route cables.

If you plan to tuck the flooring under new skirtings even better because you can easily do the vertical routes between floor edge and wall position.

While you at it run in BT, TV, Broadband / Cat 5 and any AV cables for the TV / stereo.

 

[plugwash]

Most sparkies i've spoken too seem to think if it's less than 50mm from the surface it needs to be in earthed metal conduit. I dunno if there are any explicit regs on this or not though. Conduit is a good idea anyway as it will reduce the disruption when at a future date the wiring needs replacement for whatever reason.

I would reccomend using one continuous peice of steel conduit with bends made with a bender to go from socket to socket. This will be much easier to pull cables into than a conduit with elbow peices.

 

[ColJack]

what are the ceilings? solid concrete as well?

conduits are best in this circumstance for mechanical protection..
at least 50mm from the wall for carpet grippers and things.

the 50mm from the surface of walls is part of the regulations.
if cables are not of a construction that has an earthed metalic sheath, or are not in earthed metalic conduit or trunking, or have suitable mechanical protection to prevent penetration by nails etc then it has to be RCD protected.

 

[Lectrician]

There is a reg that states cables should be 50mm below the floor/above ceiling or installed in earth conduit or the like.

When doing conservatories with solid floors we use SWA.

Use 35mm boxes (knockout is further back) and use conduit couplers and serated washers to gland the SWA to the back box. Far quicker than steel conduit, and no specialist tools required.

Cables between the concrete slab and a wooden floor on 1" battens is not compliant unless it is SWA, steel conduit or similar.

Can you not come down from above?

OR have a socket on each wall and chase horizontally between them?

 

[ColJack]

There is a reg that states cables should be 50mm below the floor/above ceiling or installed in earth conduit or the like.

that only applies to regular floors and ceilings IE, not solid ones..
it's highly unlikely that you will be nailing up plasterboard of nailing down floorboards to a solid floor or ceiling.

When doing conservatories with solid floors we use SWA.

that's a bit over the top for a few sockets..
and a lot of extra expense.. it also means that should a cable fail or need replacing it necessitates ripping up the flooring again..

 

[Lectrician]

Would you use PVC or steel conduit?

As for saying when the cable needs replacing? This just is not going to happen is it. When the cable needs replacing, the room will also be in need of renovation.

 

[plugwash]

the 50mm from the surface of walls is part of the regulations.
if cables are not of a construction that has an earthed metalic sheath, or are not in earthed metalic conduit or trunking, or have suitable mechanical protection to prevent penetration by nails etc then it has to be RCD protected.

I know that but is there a similar reg for cables burried in floors/ceilings?

 

[BS3036]

I know that but is there a similar reg for cables burried in floors/ceilings?

You know, I asked this question here some time back, and didn't get a single attempt at an answer!

I think I was phrasing it something like:

'Is a floor considered to be one big complete safe zone, or to have no safe zone at all, using the definition of safe zone applied to walls?'

and exactly the same question for ceilings.

There is certainly a difference of opinion on it, and one point which must have a bearing, is that fixing twin and earth above a plasterboard ceiling and in contact with the plasterboard is shown in BS7671 as a standard installation method.

This suggests to me a tacit implication in the regulations that the whole of a ceiling is a 'safe zone'.

I can't think of a similar argument for floors though.

 

[Lectrician]

Although with block and beam floors with suspended ceilings below, the NIC have an article somewhere with regards using steel conduit if the void is less than 2".

I can't recall where the article was...

 

[ColJack]

REG 522.6.5 is very carefuly worded to say UNDER a floor and ABOVE a ceiling.. meaning in the voids thereof..

522.6.4 A wiring system burried in a floor shall be sufficiently protected to prevent damage caused by the intended use of the floor

there are no safe zones in floors or ceilings.

account must be taken of any external influences that may be present.

"safe zones" for walls are there because joe public like to put up pictures and shelves, and the regs want to make sure that they don't put a nail through a live cable, or if they do that they won't be hurt by it.

you don't often have to screw things down to a floor or up to a ceiling other than the floorboards and plasterboard, hence the 50mm requirement through the joists.

even then you screw or nail into the wooden structure, so laying cables on top of a ceiling in contact with the plasterboard, the screw will be in the wood and likely allready in..

 

[BS3036]

there are no safe zones in floors or ceilings.

Therefore, you cannot lay a cable using Installation Method 100 or 101. Is that what you are saying?

(Not trying to catch you out, just want to understand the regulations.)

 

[ColJack]

course you can..

reg 522.6.5 is for cables passing THROUGH a joist..

or rather the 50mm / earthed metallic conduit etc, bit of it is..

the opening line of it says that: "A cable installed under a floor or abave a ceiling shall be run in such a position that it is not liable to be damaged by contact with the floor or ceiling or their fixings."

 

[BS3036]

OK - thanks, ColJack.

I've been reviewing the regs and that's cleared it up for me. I suppose that safe zones are not defined for floors and ceilings because the rules wouldn't fit well.

If you were to apply the concept of safe zones to floors and ceilings it would probably be correct to say that safe zones exists wherever there are no joists, and where there are joists there are not safe zones. This is based on the fact that you have to protect wires passing through joists, but in between the wire can be in contact with the plaster board (or presumably floorboard).

So it is understandable that the safe-zone concept is not applied to floors and ceilings, because the areas in question are not readily definable from the inside of the room, as you can't see the joists.

As a comment on the regulations as they stand (522.6.5 in particular) it means that if you are trying to fix something later on, onto a joist, you need to be particulary careful not to just miss the joist, as this is an approved place for a cable.

This post has been as much for my own benefit as anything, to clarify my thoughts, so I hope I didn't bore anyone. Blame it on the pills!