Cables in cavity with cavity wall insulation

[michaelsf90]

I'm slowly attempting to upgrade and rewire the house I'm in. Started by doing the consumer unit. Got the dno replacing my cable coming as its way past its sell by date. Got a lot of help off guys on here with what to do so thought I'd come back for some more advice

The consumer unit is at the bottom of the stairs like built into the cavity wall. It's a cupboard door and the meter and everything is there. Now the circuits for downstairs go under the floor. The circuits in between ground and first are chased into the wall. The circuits that go into the loft are fished up the cavity. I know this isnt ideal but it's what I've inherited. So I've put a 2.5 supply in for the burglar alarm and cctv supply which is on a 6A RCBO. I'm guessing the current carrying capacity is clipped direct halved? The upstairs lighting was 1mm but ive upgraded it to 1.5. Again it's a 6A RCBO. Now the big one I'm concerned about is the shower. Its 10mm on a 40A RCBO. It's been fine all this time but would I be better rerouting it?

I'm doing the full bathroom at the end of the year so I was planning on running the cable under the floor downstairs and then up a boxing in in the kitchen where the pipes go in a pvc conduit for protection. Domestic isnt my thing so even tho I'm a qualiflied electrician I'm after as much advice as possible

 

[pc1966]

So I've put a 2.5 supply in for the burglar alarm and cctv supply which is on a 6A RCBO. I'm guessing the current carrying capacity is clipped direct halved? The upstairs lighting was 1mm but ive upgraded it to 1.5. Again it's a 6A RCBO.

Why? 1mm is fine for lights even on on a 10A circuit. If you were using 1.5mm for ofther jobs and it needed replacing anyway, but...

...why 2.5mm for the CCTV, etc, on 6A MCB? That could easily be 1.5mm (regs have odd relu about lights can use 1mm but "power" has to be 1.5mm minimum). Unless you have future plans for something much bigger?

 

[pc1966]

Now the big one I'm concerned about is the shower. Its 10mm on a 40A RCBO. It's been fine all this time but would I be better rerouting it?

I'm doing the full bathroom at the end of the year so I was planning on running the cable under the floor downstairs and then up a boxing in in the kitchen where the pipes go in a pvc conduit for protection. Domestic isnt my thing so even tho I'm a qualiflied electrician I'm after as much advice as possible

Again, do you need to change it? Does it test OK (continuity & IR) and no signs of thermal stress?

If you have a genuine reason to replace it then fine, but if it is simply "old colours" or whatever then it is a waste of time & money.

 

[michaelsf90]

What is the derating factor of running up a cavity with cavity wall insulation? I put 1.5 in in case the derating factor is half of clipped direct. The 2.5 is in in case I ever need to put sockets in for cctv so I could up the RCBO size but again it depends on the derating factor. I was going to do it while doing the bathroom then it's done as il have access with the bathroom being stripped right back to its shell. In all fairness the shower looks like an add on so its newer than the rest of the wiring

 

[pc1966]

If you plan on using 13A sockets for it (not FCU or similar) then it makes sense to use 2.5mm. But really these days I would use PoE cameras as you just need network cable to them, no local power (except at the network switch or DVR).

Derating table for T&E in most cases is on page 74 of the IET On-Site Guide, also pages 65-73 has all your common circuits to see length limits and acceptable instalation methods (i.e. the derating)

 

[michaelsf90]

It's what the derating factor is for cavity wall insulation. It has the plasterboard and insulation methods and what face of the plasterboard the cable is on etc. Also my loft had insulation topped up so the insulation sits quite high. I have clipped the cables to the top of the joists as the side is impossible with all the insulation. I have routed the cables around the perimeter of the loft other than the odd switch wire which due to length ive had to clip along certain joists

 

[westward10]

These are odd questions for someone who is NVQ3 and has an AM2.

 

[michaelsf90]

My domestic experience is zero. Like I know clipping to the top of joists can be frowned upon but for me with all the insulation it's the lesser of two evils. Give me conduit and trunking and 3 phase any day! As you can tell I'm trying to avoid chasing walls and smashing my house to pieces. After the loft il slowly begin to replace cabling under the subfloor. I have two bonding cables yet I can only see bonding on my gas. So no idea where the water is bonded! Certainly isnt anywhere I can see or at the stop tap

 

[westward10]

Fundamental requirements are the same whether domestic or otherwise.

 

[michaelsf90]

Yes they are but twin and earth is a different ball game. Everything we do is swa or singles in trunking and conduit. Commercial and industrial. So twin and earth and domestic isnt my strong point

 

[westward10]

See Regulation 523.9

 

[michaelsf90]

Derating factor is 0.5. Thank you

 

[michaelsf90]

Is clipping to the top of joists a no no?