Cable in the floor?

[Toby]

Hi,

Sorry this is long! - A mate of mine has just bought a new house, with solid floors downstairs.

In the Kitchen, there is one just one 15A radial installed, with the cable dropping down to just one double socket near the internal door.

He would like a few more sockets, including a couple in the cupboards for the washing machine and dishwasher.

Is it allowed to extend this radial and then run it back to the CU to create a ring, but have part of the cable in the solid floor?

It will be protected by a 32A/30mA RCBO.

With a wall, you have to have a visible accessory and then run cables up, down or sideways from that - what happens in a floor? - we would rather not sink a box in the floor!

Assuming this is allowed, I assume the cable needs to be in conduit?

Would it also have to be >50mm deep too, or does the 30mA RCBO negate that?

The only other practical option would be to run the cable from the last socket, up the wall to the ceiling, then along to the left in the safe zone until we reach the corner, take it round the corner to the next wall, then immediately down the wall, in the safe zone, then through the wall to the under-stairs cupboard, which seems a little convoluted to me. Running it under the 1st floor is not practical, as there is a bathroom above with a tiled floor, so we would need to rip that up, or take the ceiling down in the kitchen.

On another note, he would also like to bury a 22mm gas pipe in the floor too, as it currently runs along the wall, at just above door level, and looks absolutely hideous as the boiler is in the opposite corner of the room where the gas enters - what are the rules for this, other than running it in copper, wrapped in denso tape with soldered connections, is there a minimum depth?

It, like the power cable, will need to run from the under stairs cupboard (next "room" from the kitchen), in a straight line (parallel to the wall) to appear under the kitchen cupboards, approximately 50-100mm from the wall (external wall, and will pass across a doorway to the back garden) total under floor run is about 1.5-2m, once it has got to the cupboards, it would be run under the cupboards until it is under the boiler (Old Potterton Profile 40, but likely to be upgraded at some point, hence the 22mm) then run up to the boiler. The gas hob is where the gas pipe would pop up from under the floor.

It is not practical to run the gas pipe outside, along the wall, then back into the Kitchen, as there is a door in the way, with something in the way above and below the door.

Thanks!

Toby...

[js.b1]

Check what the CU is - is it recent, circuit breakers rather than fuses still available, large enough? Check what the cable is - is it PVC of 2.5mm size or old TRS or lead? Check what the meter tails are - 25mm PVC grey outer double insulated (6181Y)? Check the DNO cutout type - modern plastic fuse-holder rather than metalclad?

He may be in for a "migration". New CU fitted via Henley Blocks (splitters) off the meter tails, with

2-3 RCD or all RCBO (bought as needed). Migrate circuits to the new CU as each cable is replaced during room redecoration.

You can do anything under Part P SI2006. However you can not change a CU nor add a new final circuit without notifying BC who will charge a fee to come and inspect it. So it comes down to what is needed re how to manage it.

Yes if the cable is in good condition and PVC rather than say TRS rubber or lead.

Solid floor means a) cable >50mm from the surface b) protected by 3mm steel which would really need to be galvanised or c) BS8436 cable which complies with 526.6 (has a foil sheath). You can not use SWA because the glands have to be accessible for inspection & testing at each end.

Why can you not run the cable around the walls or thro the ceiling void? You have corner vertical zones of 150mm and ceiling zones of 150mm. You run up or across to one of them and around.

If you have a sloping ceiling (leanto) you can use a 1G or 2G box with blank plate for routing (not particularly common but an acceptable technique re BS7671 Wiring Zones).

If the CU will take them, fine.

If you can avoid sinking into a floor, do so, particularly a kitchen as people do put screws in it (end panels for kitchen units).

You need to pick up the 17th On Site Guide (OSG) from Amazon/anywhere and a good Electrician's Guide (do an Amazon search if only as a "catalog").

As above (yes you can use steel conduit, but unless this is a straight run things get difficult).

That would be considered normal :-)

Cables should not be run through the bathroom unless they are destined for it, however the underfloor void is a grey area. In practice you would take down the ceiling if necessary below. There are also Cable Access Rods with chains, magnets, flexible & rigid fibreglass rods, lights on the end etc.

No longer denso tape.

You would use factory PVC coated yellow-ochre coiled flexible copper pipe, run in plastic conduit.

(think that is the URL) list it. Alternatively you could use Tracpipe but beware due to its plastic coated convoluted stainless steel nature it is large diameter - eg, 22mm measures out to 28mm externally. Thus you need a big trench in a floor which then begs the question how deep your screed is.

Check outside again, sometimes it can work, but yes it is ugly.

You need to find out a) what you have and b) understand how to do it re good electrician's guide. That is even if you get someone else in to do it so you can understand why / how things are done so you get what you want.

[ARWadsworth]

No the RCD would not negate that. But if it is close to a corner (15cm) between the wall and floor then no problem.

I recently used two 4mm 32A radials for a kitchen. One on each side to save the ceiling getting pulled down. Would that work in your case?

[Tabby]

That would work fine, but you need to find out what size the old cable is and ensure your mcb is within the cable's ratings. Sounds to me like extending the existing circuit.

Or you can cut 3 portals in the ceiling, one each end and one half way. Sounds like youre making a mountain out of a molehill though.

NT

[Toby]

Don't think so, as getting access to the existing 2.5 will be a pain, as it runs under the bathroom.

Having looked at it again, there is a water pipe that runs up to the right of the door that goes out to the garden, and ends up on the landing, just outside the bathroom, so we should be able to route a cable to the 1st floor under-floor void here (he wants to bury that pipe in the wall too), just means installing an accessory in line, which we can actually power the cooker hood from anyway, presuming it is OK to put this above the hood?

Toby...

[Andy Wade]

There's no >50 mm rule for cables buried in solid floors. You're thinking of 552.6.6 which only applies to walls or partitions and

552.6.5 which only applies to cables passing /through joists/ in floor and/or ceiling constructions. 522.6.4 is the relevant reg. here and all it says is:

"A wiring system buried in a floor shall be sufficiently protected to prevent damage caused by the intended use of the floor".

For a domestic screeded floor in places where drilling is pretty unlikely it's OK, IMHO, to run T&E cable in PVC conduit buried in the floor at depths of

[ARWadsworth]

It is best not to hide the power supply for an extractor behind a hood (if it is one of those tall hoods). But above a hood without a chimney is fine.

[js.b1]

It might be our kitchen fitters were a bit nasty. Whilst the kitchen units sit on adjustable feet, the end panels & corner panels got L- brackets into the floor particularly by the washing machine re wandering capability.

On a U shaped kitchen with 4 end panels (appliance cavities) there are

12 such L-brackets into the floor and a load into the worktop above.

Then again, considering the size of a floor, with a bit of ingenuity it should be possible to miss conduit buried in it.