Kitchen Island Supply with UFH

[rryles]

Looking for some advise on how to supply some sockets on a kitchen island through a floor that will have wet underfloor heating.

The floor hasn't been started yet, so I've got the choice of which layer to install it in. The complete structure of the floor starting from the bottom will be: earth, sand, damp proof membrane, 100mm rigid polyisocyanurate insulation (kingspan/celotex style), Heating pipes in clips and covered in ~70mm cement screed.

I'm thinking of installing a duct in the insulation, deep enough to be out of the way of the pipe clips. I'm open to alternative suggestions though.

The rest of the sockets in the kitchen will be a 4mm² radial on a 32A MCB. As the cable will be quite heavily derated I'm considering a lower rated protective device for this (either a fused spur or dedicated radial). I could also do with a bit of help working out just how severely derated the cable needs to be. The closest I can see is reference method A, with an ambient temperature factor.

 

[Dunc]

I would consider running a 25mm plastic conduit on top of the damp proof membrane but under the insulation, that way the conduit is as far away from the source of heat as practically possible and at it's worst will be fully surrounded by insulation for only 200mm of it's run. If it's run in 4mm i would guess you'll at least be able to bung 16A down it which would be more than adequate for a couple of sockets. I'm basing this partly on a derating factor of half for a cable fully surrounded with insulation for 500mm of its run. I don't think this figure is up to date as i think they reduced the derating factor for cables surrounded by thermal insulation in the 17th edition.

 

[Engineer54]

Unless you have a means of sealing your duct or cable through the DMP then you will have to install above it!! There's no need to go overboard on de-rating your cable(s) to this kitchen island. Use the standard de-rating factors you would normally use for finding a suitably sized cable etc. Use a heavy gauge duct, (with a decent space factor for the cable(s) as those thin walled pipes tend to deform with any sort of heat source....

 

[RogertheBodger]

How about a piece of PVC covered Pyro, bomb proof in this situation.