First Fit Advice (Wiring/Insulation)

[ecopod]

Hello to all,

I have searched forum but cannot find definitive answer. External work on extension is nearing completion (as an aside do not believe there are no good builders left, ours have been an absolute pleasure to work with) and it is now time to start planning the first fit.

Extension is standard stuff - from outside in - render and blockwork / 50mm gap / ply / frame. Putting 50mm Kingspan between frame uprights and 37.5mm insulated plasterboard.

Electrician has fed back that he'll need to get the wiring dome before the insulation goes in but I can't see how that'll work. I was assuming kingspan between frame uprights held by clips and the wiring into the gap between that and the insulated plasterboard (approx 25mm).

Any advice would be greatly appreciated as I'm keen not to be cutting into the insulation if at all possible.

Many thanks.

 

[Taylortwocities]

He probably wants to clip his cables to the brick/block backgrounds and then the cables come through the kingspan to the boxes.

You'll need to chop the kingspan to accomodate the mounting boxes anyway.

PS. Its First FIX

 

[ecopod]

Thanks for quick reply.

Do you mean cable in 50mm gap held to blockwork and then through the ply and through the insulation between uprights, that would mean more holes in insulation than I was hoping for. I've only just accepted that I'll need to cut into the insulated plasterboard.

Good spot re fit, excuse my schoolboy error.

 

[ltheb]

It would be best not to bed the cables in the insulation as this substantially reduces the current carrying capacity of the cable. If it can be sandwiched between the insulation and the plasterboards, this is ok.

 

[RF Lighting]

Is the insulation on the plasterboard polystyrene?

 

[1john]

you are cutting the kingspan in and putting it to the back of the studs up against the OSB i assume, then insulated board over studs, in which case he should come in after the kingspan, if there are any issues he only has to slip the kingspan out the way where it matters.

 

[ecopod]

The plasterboard is Kingspan K18 (CFC/HCFC–free rigid phenolic
insulation) with foil back.

Was hoping yo get wiring into gap between two so hopefully can do this, would also include trunking as extra measure.

 

[ecopod]

Seems to confirm I can go with wiring in the gap theory. 1John, spot on that is what I was hoping to do, just needed some confirmation I was not totally off beam.

I'll have a chat with electrician re order of fit, I'm putting the insulation in myself but steering well clear of electrics/cat 6/coax/etc.

No doubt I'll be back, got some flooring questions too.

 

[ltheb]

No need to spend extra money on trunking unless you think there is any specific risk of physical damage. This is a new installation so must comply with 17th edn. Cables as before should be run in the prescribed zones and all circuits should be RCD protected. Trunking is not now adequate unless you use steel conduit - no point really

 

[1john]

agreed, no need for trunking.