Cables under flooring

[charlie1377]

We are putting in a new kitchen and need to get power to an island for the hob(13amp double socket). There are a couple of double sockets I can spur off but I need to get a cable under the wooden flooring. Solid wood floor is onto joists which have insulation between them. Question is can I put a cable on top of the insulation, under the floor, which I think I can do without lifting any floorboards, only about a 1.5 meter run. Or do regulations mean I need the cable to go below the insulation?

Thanks

 

[Taylortwocities]

can I put a cable on top of the insulation, under the floor,

Yes. You might like to run this as part of the ring, rather than a spur. (2 cables needed) Otherwise your options are limited if you change things later on.
You could run a length of pipe, then you could pull in an additional cable later on.

 

[JohnD]

the hob (13amp double socket)

that sounds odd. An electric hob usually needs more power than a 13Amp plug can provide, and is a fixed appliance.

What sort of hob is it? Do you know the power rating?

 

[crystal ball]

Some induction hobs are 13 amp

 

[charlie1377]

its a Bosch induction hob, came with a moulded 13amp plug, 2 x 1.8kw, 1 x 1.4kw, 1 x 2.2kw

 

[Taylortwocities]

Ok, but guidance is that a load that large should not really be connected to a ring final. What other circuits do you have that could be utilised for this?

 

[charlie1377]

Ok, but guidance is that a load that large should not really be connected to a ring final. What other circuits do you have that could be utilised for this?

I have a 32amp cooker feed that I could use, at the moment has only an oven connected to it, however was hoping to have a spare 13amp socket available in the island as well

 

[crystal ball]

I agree a dedicated circuit would be better

 

[ericmark]

Cable is rated taking into consideration how well it can get rid of heat, so a 4 mm² cable may take load in free air but needs a 10 mm² through insulation, so some planning is required. Cables can be 60°C, 70°C or 90°C but clearly items around the cables must also stand the temperature, with mineral insulated you could go to 300°C but it would burn things around it.

The ring final has a problem in that heavy loads near the ends can cause overloading, it is designed for portable appliances in the main, and the advice is over 2 kW that a dedicated supply is used, in the main we do use a dedicated supply for oven and immersion heater even when both under 3 kW but we tend not to use a dedicated supply for tumble drier or washer/drier which likely use over 2 kW for a lot longer than the oven, the immersion heater could draw 3 kW for 5 hours so that is always on a dedicated supply.

So what we are looking at is the design, and the person signing the installation certificate as the designer has to take the loads into consideration, will the washing be done at the same times as cooking, and are they from same circuit?

Also extending a ring final the length of cable should not exceed 106 meters, we can work out existing length from the loop impedance readings so can calculate how much can be added, however likely as DIY you don't have a loop impedance meter.

So from the cooker circuit is likely a better option, and using lollipop design you can still fit a number of sockets.

There is normally some way to get the power to the device, although it may require some thinking out of the box, a square section between cooker hob extractor and centre island for example to bring in services. With mothers kitchen they ran steel wire armoured cable around the house to get power to kitchen, there is always a way.

It does not say where you live, where I live this work is notifiable, but even if not, should really be done by some one who knows what they are doing.

 

[charlie1377]

I live in the UK. I have tried to get en electrician to do the work, however having failed to turn up for 3 consecutive weeks and then not returning calls etc for a few more weeks I have run out of patience and decided to do it myself! Sounds like a feed from the cooker circuit is the best option, and we can do without the extra socket. Main question is whether I can lay the cable on top of the kingspan insulation, so between insulation and floorboards, which I think can be done without lifting any floorboards or whether I need to take up floorboards in order to run the cable underneath.

 

[ericmark]

The regulations refer to suitable protection but don't state what that is, it says

522.6.4 A wiring system buried in a floor shall be sufficiently protected to prevent damage caused by the intended use of the floor.
522.6.5 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. A cable passing through a joist within a floor or ceiling construction or through a ceiling support (e.g. under floorboards), shall:
(i) be at least 50 mm measured vertically from the top, or bottom as appropriate, of the joist or batten, or
(ii) 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
(iii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a protective conductor, or
(iv) be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the requirements of these Regulations for a protective conductor, or
(v) be mechanically protected against damage sufficient to prevent penetration of the cable by nails, screws and the like.
522.6.6 A cable concealed in a wall or partition at a depth of less than 50 mm from a surface 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 enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a protective conductor, or
(iii) be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the requirements of these Regulations for a protective conductor, or
(iv) be mechanically protected against damage sufficient to prevent penetration of the cable by nails, screws and the like, or
(v) 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.
522.6.7 Where Regulation 522.6.6 applies and the installation is not intended to be under the supervision of a skilled or instructed person, a cable installed in accordance with Regulation 522.6.6 (v). and not complying with Regulation 522.6.6 (i), (ii), (iii) or (iv), shall be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.

So there is nothing to stop you using steel wire armoured cable in the floor. However in the main it is common sense, one can argue until the cows come home who is a skilled person etc. In the main you want it safe, and done in a way that if in the future you want to rent the property, the person doing the EICR is not going to fail it.

Please note I don't have BS7671:2018 there may be changes to what I have quoted.