dumb question - what's the purpose of electrical conduit below the plaster?

[tonyjeffs]

I always tend to think of conduit as protection against screws and nails, but clearly it isn't since a nail'd go straight through.

Perhaps cable embedded directly in the plaster could corrode, or become damaged? But although I've seen plenty of unducted cables in plaster, they seem to survive ok.

Or perhaps the air gap around the cable helps with temperature control?

Or perhaps it just encourages neatness.

What's the official reason?

To

PS, a bit late in the day, but I'm very sorry to hear about Andy Hall. Sadly I didn't get to know him. He gave me lots of good advice on my occasional visits here. One of the good guys,

[Micky Savage]

Hi, It is to protect the pvc outer sheathing from limein the plaster. I thought the same as you. I asked at Coledge. Was told this from one of my Tutors.

Kind Regards

Micky.. LEEDS.

[Andrew Gabriel]

If you're thinking of the capping and oval trunking in plaster (which isn't quite the same as conduit)... Holds the cable in place until plastered. Protects the cable from the plasterer. Enables the cable to be replaced without replastering.

Actually, the opposite.

Yes, that too.

There's no requirement to use capping/trunking.

[dennis]

If you are using steel conduit that screws together you will notice if you try and nail it. That sort of conduit replaces the outer sheath on the cables and you can pull "singles" through.

There are other lightweight conduits in plastic and pressed steel that don't offer as much protection. As well as really lightweight stuff like capping that is only there to protect against a ham fisted plasterer and nothing else.

At least with metal conduit you can now earth it and comply with the 17th edition without an RCD.

[Dave Plowman (News)]

It wouldn't go straight through *proper* steel conduit.

Indeed - the use of plastic conduit buried in plaster only really serves to make wire replacement possibly easier. And may also be easier to fix to the wall before plastering than naked cable.

Dunno.

[Dave Plowman (News)]

Not quite sure how PVC conduit would protect PVC wiring?

[Tim S]

dennis@home coughed up some electrons that declared:

I believe you can put singles in PVC conduit[1] and trunking (but not slotted trunking).

[1] I'm not sure about oval conduit in this respect.

What heavy steel conduit (or steel trunking) buys you is compliance with regulation 522.6.6 (17th) (IIRC, book's at home) regarding protection of cables - the other options being:

Use MICC or SWA Armoured or Earth Screened to a certain BS (eg XL Shield, but not FP200;

Bury > 50mm below wall surface;

Protect with There are other lightweight conduits in plastic and pressed steel that

That's my understanding too.

Indeed, but given the difficulty in working with heavy steel conduit (the bending, the cutting and the threading) personally I'd look to XL-Shield type cable as one option and SWA as the other option - it's much easier to handle.

Cheers

Tim

[Steve Firth]

I'm glad it's not just me thinking that. And how much modrn plaster is lime based?

Anyway, my home is plastered in lime with added goathair to satisfy the LBO. Several places have PVC sheathed cable buried beneath the plaster. Recent work in the kitchen exposed cable that has been buried for 18 years in lime plaster, no sign of deterioration in the T&E sheath.

[Anna Kettle]

Yes I think the lime story is twaddle too. OK if it were to sit in a bucket of as-yet-unset lime there might be a problem but on a wall the lime will set and once it has done that it is pretty inert and not going to affect PVC

Anna

-- Anna Kettle Lime plaster repair and conservation Freehand modelling in lime: overmantels, pargeting etc Tel:    (+44)  01359 230642 Mob:   (+44)  07976 649862 Please look at my website for examples of my work at:

 

[Steve Firth]

Some of the buckets with self-sealing lids which the coarse stuff we bought from the local lime center was packed in were PVC. I've had one standing outside for a couple of years. Again no sign of deterioration and that's been in contact with wet lime continuously.

[neverwas]

LBO please?

[Steve Firth]

Listed Buildings Officer

[neverwas]

VMT

[The Medway Handyman]

Vehicle Miles Traveled? Vending Machine Trip? Valve Material Type?

[Fred]

Do you mean conduit or channelling?

I've used channelling before. I use to use galvanised steel channelling and one set of regs said you could use short lengths of conductive mechanical protection without earthing it. What do the new regs say?

It was nice to know that if you tried drilling through plaster I was confident that a drill would stop at a thin sheet of galvanised steel channelling and though it sad it was effectively outlawed.

[neverwas]

[dennis]

You probably can, I wouldn't, but that's just me being extra cautious.

[dennis]

I don't know what drills you use but mine will go through steel capping as if it wasn't there. They go through reinforcing bars in concrete so a bit of tin isn't going to stop them.

[Dave Plowman (News)]

A standard masonry drill won't - the cutting angles are wrong for steel.

[Tim S]

dennis@home coughed up some electrons that declared:

OK, think I have the regulation, but I'm not qualified so this is open to interpretation:

IEE Wiring Regs, 17th Ed.

521.10.1: "Non-sheathed cables for fixed wiring shall be enclosed in conduit, ducting or trunking. This requirement does not apply to a protective conductor complying with Section 543.

Non-sheathed cables are permitted if the cable trunking system provides at least the degree of protection IP4X or IPXXD, or if the cover can only be removed by means of a tool or a deliberate action."

The IP ratings come down to "can't get a 1mm probe in".

BTW - I'm practising looking up regs to order for my upcoming exams, not being a smartass :)

Anyway, if you look at it from another angle, the (plastic) conduit or trunking is taking the place of the sheath, no more and no less. "Mechanical protection" is a different game and that's where steel comes in.

It was certainly a method employed in the last university I worked at, (singles in plastic trunking).

Cheers

Tim