How proud should back box be from face of thermalite? (etc)

[Draughtsman]

1. I need to sink a back box into a new thermalite wall before render/skim go on. Approx. how thick will the render/skim be? (how far proud of thermalite face should I set the box?)

2. What is that plastic cable protection that goes under the render called? Is it still legal? The image shows a very short length just showing at the bottom of another wall, below a socket.

 

[flameport]

Approx. how thick will the render/skim be?

Depends entirely on the type of finish you are having put on there. Ask the plasterer.

What is that plastic cable protection that goes under the render called

Capping, it's still available. It is not cable protection, it's just used to hold the cables in place.

 

[Draughtsman]

Ah, PVC Channel in 25mm and 38mm from Screwfix.

 

[Iggifer]

16mm-ish is the 'usual' depth for wet+skim. I say usual because it can vary on the same wall. I very rarely chop in a 16mm box (unless asked).

So if you chop 10mm off the thermalite (for a 25mm box) that should be fine. But check with your plasterer.

 

[ban-all-sheds]

Are you replacing an existing back- or surface box, or is this a new socket?

 

[Draughtsman]

New thermalite inner leaf - new socket. New sockets going elsewhere in room, into conc. inner leaves.

 

[ban-all-sheds]

Are you aware of the rules for concealed cables?

 

[Draughtsman]

There are rules?

I'm putting one socket into a new thermalite wall, and one or two more into the other original conc. block walls. The room is on the 1st floor and the room below has no ceiling yet, just the exposed joists so I'll be running the cables along the joists and then vertically up the walls to the sockets. Are there any rules about where to site cables on joists? They're 200 deep, I thought mid height would be ok?

 

[Iggifer]

That's fine. BAS is referring to concealed cables in walls.

If you're dropping down vertically to each socket that's fine.

What you cannot do is go diagonally at any point etc.

If you google 'cable safe zones' there's diagrams that will show this clearly

 

[EFLImpudence]

...and this for Building Regulations regarding drilling joists:

 

[ban-all-sheds]

There are rules?

http://electrical.theiet.org/wiring-matters/27/cables-in-wall.cfm?type=pdf

 

[Draughtsman]

That's interesting, thank you.

 

[Draughtsman]

Hmm.. I don't even have a circuit breaker, and my fuse box is in the bathroom (it wasn't originally, but a wall was removed before I got the place, so now it is).

This extension has building regs so maybe a sparx is needed here. Presumably I can still chase out, fit back boxes, feed a few cables thru joists etc.

 

[ban-all-sheds]

Sorry - you're building an extension?

If so, what did you say, or by default allow your LABC to assume, would be the way that you'd ensure that the electrical work would comply with Part P?

If you don't do whatever that was you may find yourself being refused a completion certificate.

 

[Draughtsman]

Yes, the original planning application was many years ago and I since got approval for a revision to the original plans. It was started so long ago that I doubt that part P existed at the time.
Incoming mains supplies were accommodated correctly thru a box-out in the footing, but beyond that there is no mention of any electrical works on any of the paperwork from all parties involved, at all.