Capping / Conduit for wiring

[MortarThePoint]

We've a lot of blockwork walls which are to be wet plastered. This means we'll have lots of cables chased into the blockwork and then plastered over. As I understand it, there are two main reasons to using capping:

• Protection: to protect the wires from the plaster's trowel, won't protect against screws or nails
• Rewiring: you have a chance of pulling/pushing wires through and so don't need to disturb the plaster if rewiring.

The alternative is to just chase and clip the wires to get plastered over.

 

Chasing limits 1/3 width of blocks if vertical, 1/6 if horizontal. So for 100mm blocks that's 32mm and 16mm respectively.

 

I'm inclined to use the oval conduit pictured below chased into the blockwork. The main benefit is the rewiring one as I see it, because chased wires should be protected enough against the plasterer. I'm doing the wiring myself so can take the time to include the conduit. I'd like it in 3m lengths (2.7m ceilings, 2m works well for 2.4m ceilings), but Screwfix don't carry that, though this page says it is made. The datasheet says it's 1 cm deep, but drawings of other brands suggest 11mm external, 9mm internal.

 

I have read wires outside conduit dissipate heat better which makes sense.

 

What did others do and how realistic is to to rewire through these?

 

 

Falcon is another option and this supplier looks well priced:

    https://www.superlecdirect.com/p-oval20-falcon-20mm-pvc-oval-conduit/

 

TLC unbranded and expensive:

• Dimensions: External: 22.5mm x 11mm Internal: 20.0mm x 9.17mm : https://www.tlc-direct.co.uk/Products/MTOV20.html
• Dimensions: External: 29mm x 11mm Internal: 25.0mm x 9.90mm : https://www.tlc-direct.co.uk/Products/MTOV25.html

[nod]

Metal capping for wet plaster 

[MortarThePoint]

6 minutes ago, nod said:

Metal capping for wet plaster 

 

Thanks, why is that? Personal preference, standard practice or regs?

[TonyT]

Plasterer’s sharp trowel!

[nod]

Plaster isn’t that great over plastic 

Metal will fix flatter

Also conduit will need chopping into the block work for wet plaster BC  don’t always allow 

[TonyT]

If you are going for something that’s rewirable

 

Use conduit and adaptors 

[Onoff]

You can save on wiring by going horizontally between sockets. A wall chaser makes it a doddle if you get a decent extractor on it.

[MortarThePoint]

19 minutes ago, nod said:

Plaster isn’t that great over plastic 

Metal will fix flatter

Also conduit will need chopping into the block work for wet plaster BC  don’t always allow 

 

I plan to chase it in and the chase depth looks to only need about 12mm. Can check with BCO that he'd OK. I don't have any hollow blocks.

 

12 minutes ago, Onoff said:

You can save on wiring by going horizontally between sockets. A wall chaser makes it a doddle if you get a decent extractor on it.

 

Most will need to be vertical due to the layout. I have a chaser and will see how the dust extraction works.

Edited January 15, 2022 by MortarThePoint

[Russell griffiths]

You need to look at your lighting circuits and intermediate switching, you might find that you need something a bit bigger than that conduit. 

One light switch I have has 16 cables going to it. 50x50 trunking needed. 

[PeterW]

2 hours ago, MortarThePoint said:

Rewiring: you have a chance of pulling/pushing wires through and so don't need to disturb the plaster if rewiring.

Why are you planning for something that will not be needed for 40-50 years ….??

 

2 hours ago, MortarThePoint said:

I'm doing the wiring myself

In that case you’re qualified to answer your own question. If you can’t, you’re not qualified to do the wiring. 
 

 

[MortarThePoint]

2 hours ago, PeterW said:

Why are you planning for something that will not be needed for 40-50 years ….??

 

In that case you’re qualified to answer your own question. If you can’t, you’re not qualified to do the wiring. 
 

 

 

Rewiring includes us concluding we want an additional socket etc somewhere.

 

I know that it's not required by regulations, but wondered more about people's experiences and preferences

[ProDave]

12 minutes ago, MortarThePoint said:

 

Rewiring includes us concluding we want an additional socket etc somewhere.

 

I know that it's not required by regulations, but wondered more about people's experiences and preferences

My preferred method is create a proper 25mm service void made of battens and then covered with plasterboard.

 

This allows you to run socket cables horizontally from socket to socket.  As long as you have at least one socket on each wall, you create a safe zone all the way around the room where it is simple to add extra sockets anywhere you want to by doing little more than cut a hole in the plasterboard, fish out the cable and fit a socket.

[MortarThePoint]

On 15/01/2022 at 13:42, Russell griffiths said:

One light switch I have has 16 cables going to it. 50x50 trunking needed. 

 

Wow, that must look interesting! I presume that's one panel of many switches.

 

I'm not expecting anything that busy.

[MortarThePoint]

There's been lots of planning and not much doing what with a pick up in day job demand.

 

I'm starting to doubt the benefit of using conduit/capping at all for sockets. If chased into the wall, e.g. with a 15mm x 10mm chase. With a 10mm chase depth it would be an amazingly cack-handed plasterer who managed to damage a cable. 

 

Oval conduit is pretty cheap (£0.35/m) so it's not so much of a cost decision. As @PeterW say's, complete rewiring is likely far down the line, and how many modifications would actually be made easier by conduit. Adding a new socket might be midway between two existing sockets and so benefit from the conduit. I think I am already leaning towards an excessive number of sockets (four 2-gangs per bedroom) so it feels unlikely I'd want more. Maybe using conduit in selected rooms that are more likely to need changes, like the living room. Oval conduit in some ways feels a bit like insurance against making some mistakes.

 

Conduit for wired data connections is a no brainer on the other hand.

 

Edited February 27, 2022 by MortarThePoint

[MortarThePoint]

Some relevant extracts from the Onsite Guide:

------

This is poorly written as everything I have seen suggests its (a) or (b) or (c) or (d) or (e) or (f) but there is no or at the end of (b) here.

[ProDave]

I would think you WOULD be using an RCD, unless you are for some reason trying to find a reason not to?

 

Otherwise just fit them in safe zones is the only requirement.

[MortarThePoint]

Just now, ProDave said:

I would think you WOULD be using an RCD, unless you are for some reason trying to find a reason not to?

 

Otherwise just fit them in safe zones is the only requirement.

 

One better, I'll be using RCBOs which is effectively an RCD for each circuit.

 

I wanted something to highlight that capping / conduit is nothing to do with protecting cables beyond he plastering stage.