2.5mm T&E in 16mm oval PVC conduit - short run

[sim17]

I'm installing insulated plasterboard (Gyproc Thermaline 60mm) on inside of exterior walls of living room using drywall adhesive. I'm also moving the sockets that were on the wooden skirting up higher and off the skirting (I was advised at periodic inspection they shouldn't be on the skirting).

Raising the sockets to 45cms from the floor I need to run the ring main cables up behind the plasterboard. I was planning to use 2 x 50cms length of oval pvc conduit (separate conduit for each ring cable) up to the socket. I know I musn't embed in the insulation. If I use 16mm oval I shouldn't need to grind/chisel out any brick, the conduit will be in the cavity between the plasterboard and the brick wall. I think 20mm will be a little too thick and require some chiseling to embed in brick so that the board sits happily.

But reading other posts on this forum I see T&E isn't really meant to go in conduit.

As it is only a short run, and one T&E cable per 16mm oval does leave some room for the cable to "breathe", does this sound OK? Or is just covering the T&E with PVC capping better? Or even chisel a channel and then use capping.

In another room I've already used 25x16mm pvc channel to carry a fused spur from ceiling to floor (in "safe" zone above fused junction unit) behind the same Thermaline board but that wall was plastered so I had a bit mroe room chiselling the plaster away. Given that that was a longer run and to be on the safe side for any derating I actually used 3 or 4mm T&E for that. Again is using such as rectangular pvc channel around a single T&E cable a problem? Would rather get it right than have someone come along later and think it looks duff. Not that I fancy taking the board off now...

 

[ban-all-sheds]

If I use 16mm oval

You might find 19/20mm an easier fit.

the conduit will be in the cavity between the plasterboard and the brick wall.

What cavity? You said you were gluing the board direct to the wall...

But reading other posts on this forum I see T&E isn't really meant to go in conduit.

It's no good for pulling into a conduit system, but short straight lengths of oval conduit are no problem.

As it is only a short run, and one T&E cable per 16mm oval does leave some room for the cable to "breathe", does this sound OK? Or is just covering the T&E with PVC capping better? Or even chisel a channel and then use capping.

I don't see why you need capping, and clipping it direct to the brick wall will give it better heat dissipation than putting it in conduit.

But how are you going to mount sockets? Surface patresses on the board? You can't recess them...

And then you'll have to perforate the vapour control layer to pass the cables through.

Why not glue foil-backed insulation to the wall (e.g. Celotex GA3000 , then batten on top of that, then board it out. Run the cables in the cavity between the boards and the insulation. That way you can have flush mounted accessories and no problems with vapour seals...

 

[sim17]

Thanks for the quick reply.

I'm hoping I've got this right - I did check with an electrician and consulted the Gyproc technical information about the product.

The Gyproc white book specifies a cavity of about 10mm between board and wall for the TL system and thermal board. The adhesive is applied in a regular pattern with continuous ribbons round the perimeter, a minimum of 20% coverage but not the whole wall. So there is a gap into which services can be introduced as indicated in the white book.

The plastic insulation on cables can react if it comes into contact with polystyrene and the Gyproc specs say cables must not touch the insulation, so conduit, capping or channel makes sure that is prevented, I guess that's why conduit is indicated.

I'm intending to follow the Gyproc spec for sockets in partition walls by cutting back the insultation around the recess and introducing a plasterboard bafflebox (I have some spare bits of pink fire board). The recess will also be sealed using the specified Gyproc sealant, and I'll use plastic recessed pattress boxes designed for plasterboard. It is true the VPC and insulation at that point will be compromised but the sealing should help.

Your suggestion for celotex, battens and standard board sounds good although I'm not working in a large room. The Gyproc product gives maximum thermal performance for minimum thickness and is a single fix - to get the same effect with separate insulation, batten and boards would lose more room space. Sounds a good idea for larger rooms though.

 

[Adam_151]

Thanks for the quick reply.

The plastic insulation on cables can react if it comes into contact with polystyrene and the Gyproc specs say cables must not touch the insulation, so conduit, capping or channel makes sure that is prevented, I guess that's why conduit is indicated.

Thats true...the PVC sheathing will react with the polystrene, the same will happen with pvc conduit... now whether the conduit will act as a sacrificial element and protect the cables, just itself going a bit gooey on the outside... or whether over the years the whole thing... conduit and cable will turn into a stickly gloop, I cannot tell you!

I'd probably use some metal capping if it were me though...

 

[ban-all-sheds]

Thats true...the PVC sheathing will react with the polystrene, the same will happen with pvc conduit...

But there's no plasticiser in conduit.

And anyway - is the Gyproc product polystyrene? Or PIR?

 

[sim17]

Gyproc Thermaline Super board I'm using is phenolic foam rather than polystyrene.

The phenolic foam is backed by glass fibre reinforced aluminium foil and glass fibre tissue on the other side.

This gets more complicated the more you think about it. If only I'd done a chemistry degree.

 

[RF Lighting]

Gyproc Thermaline Super board I'm using is phenolic foam rather than polystyrene.

Is that like the same stuff as kingspan is made of?

 

[sim17]

Kingspan make a lot of different products.

If you mean TW50 - that's rigid urethane.

If you mean Kooltherm K8 that's phenolic, like the Thermaline Super

I dare say they do polystyrene somewhere in their range too.