Electrical Conduit...

[Minkeycat]

I'm undertaking a project curing the cause of a damp issue and soon need to have a go at lime plastering having taken the wall covering back to cob on a stony base. In doing so, I've discovered that the power running to a wall light and an electrical socket was unprotected (beyond its own insulation) and simply plastered into the wall. I'm thinking I should probably take this opportunity to run it through a conduit but I'm not sure what to use. I've used conduit before in plasterboard walls on other houses and presumed that if they were accidentally drilled into, as they weren't fixed, they'd mostly move out of the way. I was told by someone locally not to bother with conduit at all as if someone drills into it, it'll be plastered in place and the drill will simply go through it and into the wire as it won't be able to move but at least it'd make it easier to get a new wire down so there must be some benefit and it's not expensive or difficult to do so I probably ought to do it. Or is this something that I have to get a qualified electrician in to do which seems a bit of overkill for putting 2m of wire through a bit of conduit that I can buy on eBay?

So if someone could advise me as to the best type and spec of conduit for this little job, I'd be grateful.

 

[Abi Cott]

I've always been told that the idea of the metal cover is that a masonry bit will skid on the surface. An hss bit would go through, but who drills a wall with an hss bit?

 

[Flyfisher]

Electrical conduit is mainly 20mm, whether metal or plastic. It would certainly make re-wiring easier, if the time comes, but it requires a lot of channelling into a wall to bury it deep enough for a decent covering of plaster. I've never come across completely buried conduit, though that's probably not saying much and there might be loads of it out there! All the conduit I've come across has been surface mounted.

What I've found mostly used within plastered walls is that 'stepped plastic' stuff that used to cover cabling before plastering. It is nowhere near 20mm so requires less channelling to the walls but holds the cable so tight to the wall that the ease of rewiring can be a bit hit or miss.

To be honest, I'm not sure what the regs require, but any plastic covering will provide minimal protection against errant drilling so I'm not entirely sure why cables are not routinely buried in the plaster. Adverse reaction with the plaster perhaps? From a performance perspective I'd have thought a buried cable would be able to dissipate heat better than a covered/conduit one as the surrounding air would have some insulating effect.

 

[Damon]

Is the wiring to the outside light just a single cable or a loop in, loop out and switch cables?

I'd definitely put it in some conduit as like you stated you can always remove and refit the wire at a later date without digging the plaster back out the wall.

For a single 1.5mm T&E cable I would recommend this -
https://www.screwfix.com/p/tower-oval-conduit-16mm-x-2m-white/91802

Oval conduit is what you want for burying in plaster. The round stuff is generally for surface laying.

Best wishes,

Damon

 

[88v8]

Oval conduit is what you want for burying in plaster.

Gosh, so long since I did any rewiring I'd forgotten oval conduit. There are wall clips for it but they make it fatter; the flattest way to fasten it against the wall is a length of galv wire attached to a nail/(brass) screw each side.

In terms of not drilling buried cables, I believe the protocol is that they should run vertically down to light fittings & plugs, rather than wiggling in a random fashion. Our buried cables wiggle around in the pointing between the coursed rubble stonework. Fortunately the cable finder has been invented.

Ivor

 

[Minkeycat]

Oval conduit eh? Thank you for that suggestion, I'll look into it.

The wiring is all internal and can be channeled into cob which is very easy so 20mm isn't potentially too bad an option for now and seems quite cheap but I'll check out the oval stuff.