Is conduit necessary when hiding mains wiring in plaster?

[LouisB]

Please can you help me.

I want to know whether conduit is necessary when hiding mains wiring in plaster?

The Collins DIY Manual (1986) says :-

"Some people cover all buried cables with a channel but it isn't required by the IEE Regulations. Cables buried in light plastic conduit can be withdrawn later .. but the need is so rare in a house as to be hardly worth considering".

If it is hardly worth considering why do shops sell conduit.?

However a plasterer who visited our house said that all exposed cables should be covered by a conduit before plastering as the lime in the plaster can attack the cable insulation.

Is this true?

Please let me know what you recommend and whether I should use conduit to cover all the exposed wiring before plastering.

Also what is the recommended depth that uncovered wiring should be placed below the plaster?

Do you have any tips or tricks to avoid the need for conduit?

Thanks Louis B.

[Dave Jones]

Why are u getting it plastered? Plasterboard is cheaper, quicker and will also save on the heating bills, and no need for conduit!

Dave

[chris French]

In message , LouisB writes

No. But you can use it.

Because some people find it worthwhile?

No it isn't.

I usually use oval conduit for my cables, it doesn't cost much or take much time, and the cable would need fixing anyway, and if I was to want to remove the cable I can. An alliterative is plastic capping, though I find that hard to fix on my walls. but you don't need to bother if you don't want to.

So as the plaster will go over the top :-) - it doesn't matter as long as you have a a few millimetres clearance,

[LouisB]

Plasterboard is not really appropriate as the wires are in narrow channels cut in the old plaster by the electrictions.

Louis B.

[Mungo "two sheds" Toadfoot]

He may have said that because plasterers are notoriously = sparks-unfriendly and will hack lumps out of bare cables or "hide" them = for you if they're in their way. Not maliciously, but just because of = the way they work and the tools they use.=20 Plastic capping is a good idea if you're employing a plasterer - less = chance of damage to the cables and it's cheap. Use galvanised nails to = fix it though, or rust spots will come through.

Plus I think capping gives *a little* more mechanical protection to the = cables. Not much, but some!

Si

[Mungo "two sheds" Toadfoot]

Apologies for the formatting - I'll sort that!

Si

[Lurch]

On 19 Jun 2004 12:20:55 -0700, [e-mail] (LouisB) strung together this:

Not really, it just gets fitted as the norm.

Depends on what you mean by conduit, some types of trunking and conduit are for surface mounting, some are for flush mounting.

Never heard that one before, wouldn't say it isn't true though. I'm sure someone will come along with some sort of chemical equation.

I usually fit it, the regs only require it for mechanical protection during the plastering stages, e.g. the plasterer damaging it with his trowel, after that stage it's pretty useless at stopping nails and drill bits!

As long as it's below the surface, that'll do it.

Not really, fit if you want, if not just clip the cable to the wall.

[Lurch]

On 20 Jun 2004 01:05:47 -0700, [e-mail] (LouisB) strung together this:

Plasterboard is attached to the wall with a 10-20mm gap behind it in which cables and pipes etc... can be run.

[Nige]

I'd suggest that the plaster depth is at least 3mm on top of the cable, otherwise it is easy to break.

[Dave Liquorice]

Galvanised is cheaper still...

[Dave Stanton]

< long line lengths removed>

Mungo

Could you check your line lengths

Dave

[Dave Plowman]

It's ok here so I'd say you're within the permitted line length.

[John]

IIRC the corrosion/material suitability chart which used to be doled out periodically with the Process Industry trade mags, such as whats new in processing, gave PVC as being resistant to most of the common reagents including quite "strong" alkalis and acids so its very unlikely that anything present in mortars or plasters will have any effect on PVC cable sheath. Now styrene vapours in quite low concentrations from polystyrene insulation is another matter altogether.

[Lobster]

Hey, tell me about it. Having completed my rewiring, I didn't fix any of the socket faceplates before getting the plasterer in last week, as otherwise I knew he'd just plaster them in, ie recessed below the surface - yuk. However, after he'd left I had to go round with hammer and chisel to hack out dried plaster from all the electric boxes... I'd have expected to have to break bits off the edge of the holes, but (despite there only being about 3mm of skim plaster here) this guy had managed to virtually fill all the boxes, some were barely even visible (and I knew where to look for the boxes!). By the time I'd fully re-exposed them all, I was left with plenty of damaged-edge holes which will polyfilla-ing before I can fit the faceplates... I really must go on that plastering course!

David

[Nige]

Could you check your anal retention?

[Dave Plowman]

You should have used a sharp old wood chisel and with care you'd not need to make good the edges.

[Dave Liquorice]

Or better cut round the outline of the boxes whilst the plaster was still "plastic".

[Mungo "two sheds" Toadfoot]

Could you check the post I sent one minute after the first?

Si

[Martin Angove]

Nah he's not - look at the raw posting (save the raw message to a RAM disc and look at it in something like StrongEd or Zap with end-of-line markers turned on) and his paragraphs are each one long line - several hundred characters. IIRC the "netiquette" is to keep somewhere around 70 chars and hard wrap (StrongEd's email settings hard wrap at 72 characters). I suspect that Pluto is wrapping the lines for you. Messenger doesn't do that properly and splits words.

We shouldn't pick on Mungo though; there are several people in this group who have the same problem.

As for capping: I really can't see the point. The plastic stuff offers absolutely no protection whatsoever and is just as difficult to stick to the wall as cable clips, and the galvanised stuff *must* be earthed according to the regs, which is a bit of a painful process. As for being able to withdraw / replace cables, I have yet to meet the installation using capping where that is possible. There's usually a kink or a gap or a crushed bit or a couple of inches at ceiling level where the capping is missing. Not worth bothering IM(limited)E as you usually have to dig it out anyway!

The oval conduit is slightly better, but means a deeper channel must be dug in the wall in order to be able to plaster over it. With just the cable and a few clips it is often possible to channel out just the existing plaster to give enough depth. Anything additional means hacking into a column of bricks or stones or blocks which can cause serious grief.

Hwyl!

M.

[Martin Angove]

[...]

Just a possibility, but if it is the lime which attacks the (PVC) cable (do all plasters contain lime?) surely that would also attack PVC capping?

[...]

*So long* as it is run within the "permitted zones". Outside these zones you must either bury it more than 50mm deep or mechanically protect it - and this doesn't mean plastic capping.

Hwyl!

M.