PVC Channel: It's rubbish

[richard7761]

I wonder what other misconceptions and areas of ignorance you have of the Wiring Regulations, given that you have taken it upon yourself to do wiring?

If this is part of your building project, what did you say would be the way you'd comply with Part P when you applied for Building Regulations approval?

I actually did a course in electrical installation and maintainance years ago. And I will have no problem putting in this wiring that will be better workmanship than exists in the current wiring that was practically thrown in when the house was rewired by "professionals".

 

[ban-all-sheds]

Be that as it may - what did you tell your LABC?

 

[ban-all-sheds]

Ban, before you so flippantly dismiss this, there is a regulation requiring wiring and other parts of the installation to be protected from damage.

Capping is one way to protect cable from the damage caused by plasterer's trowels.

There is also a very widespread belief that capping is not needed to protect cables from plasterers trowels because the last thing they want to do is to damage the edges on them by hacking at cables.

And please note that the OP was only trying to use it because he thought the regs required it, not because he feared the mad trowel-man.

 

[JohnW2]

There is also a very widespread belief that capping is not needed to protect cables from plasterers trowels because the last thing they want to do is to damage the edges on them by hacking at cables.

There is, indeed, such a widespread belief, and it's undeniably true that I have very rarely used capping myself (at least, not for many years). However, I don't think that all plasterers are necessarily as cautious as you suggest - since they know (maybe from experience!) that they can easily slice through the sheath, and perhaps a fair bit of the insulation, of cable without doing any harm to the edge of their trowel.

In the context of this forum, those undertaking DIY electrical work may well also be undertaking DIY plastering - and thus will usually have appreciably less skill than a plasterer, and very probably much less concern about the state that their (probably very rarely used) trowel ends up in.

Kind Regards, John

 

[mfarrow]

Another misconception I've heard spoken about on here in the past is that plaster reacts with the PVC. This is not true, and indeed BS 6004 has an installation related appendix which lists one of the methods as being buried in plaster.

I'm sure doing chases that even the most amateur can avoid slicing through the cable. If it were a bare wall which required browning then that's a different matter and the plasterer's trowel will be nice and sharp at the edges no doubt after a few years on the job.

 

[JohnW2]

Another misconception I've heard spoken about on here in the past is that plaster reacts with the PVC.

If that were true (and a problem) we most certainly would know about it by now!

Another I'm sure doing chases that even the most amateur can avoid slicing through the cable. If it were a bare wall which required browning then that's a different matter ...

If one really has 'chases' of sensible width and adequate depth (with cable clipped at bottom of chase) then I agree that it would be next-to-impossible for anyone to damage the cable with a plastering trowel. However, some of us live in old properties and 'enjoy' the situation in which it's far from unknown for 12 inch squares of full-depth plaster to fall off when one starts 'interfering' with the wall (e.g. to create a chase). Once that situation arises (effectively a locally 'bare wall') then, as you say, the scope for damaging the cable whilst replastering becomes very real.

Kind Regards, John

 

[sparkwright]

You only have to see the damage plasterers can do coiled up cables in the back boxes. Sometimes the damage can go beyond the sheath.

They are also quite good at bending the fixing lugs on the boxes.

 

[ericmark]

The old tin capping was liked by plasters as it did not flex like the cables and made it easier to plaster. It also gave a warning when drilling with care most would realise without reaching the cable below. I am sure the plaster would catch cables to get electricians to use capping and make there job easy.

However in 2008 the old metal stuff became a problem since it was in the past not earthed new regulations made the use of tin capping likely non compliant so no option but use plastic however this stuff flexes worse than the cable and does not make it easier for the plaster so I would expect the practice of catching with trowel has stopped. Neither does it help when drilling through wall you don't realise you have hit plastic capping.

Oval plastic conduit does hold cables firm and is reasonably easy to plaster over and I have on odd time even replaced a cable in it but although theory allows replacing with capping in practice does not work. Oval conduit also does not need as much width in plaster.

Metal conduit normally too thick to go behind plaster without removing brick as well.

Twin and earth is flat so lies well and Ali-tube well protected and easy to trim so can't see why one uses capping any more.

 

[sparkwright]

Plastic capping is ideal in new builds.

Plasterers prefer it, as it's thin. They cannot and will not plaster over an oval conduit directly nailed to the brickwork.

Obviously drylining over brickwork doesn't cause so many problems.

I have successfully replaced cables in capping. Practically impossible with long lengths of 2.5 mm2 on socket circuits.

But easy on lighting rewires. Have successfully replaced t&e switch wires for 3&e when making two way circuits in bedrooms. Have also made wall lights higher up without a massive amount of damage.

Well worth using, costs pennies, looks professional, is professional, and gives some peace of mind.

 

[ban-all-sheds]

They cannot and will not plaster over an oval conduit directly nailed to the brickwork.

I'm sure they won't.

But they absolutely can.

 

[pred]

There is also a very widespread belief that capping is not needed to protect cables from plasterers trowels because the last thing they want to do is to damage the edges on them by hacking at cables.

There is, indeed, such a widespread belief, and it's undeniably true that I have very rarely used capping myself (at least, not for many years). However, I don't think that all plasterers are necessarily as cautious as you suggest - since they know (maybe from experience!) that they can easily slice through the sheath, and perhaps a fair bit of the insulation, of cable without doing any harm to the edge of their trowel.

In the context of this forum, those undertaking DIY electrical work may well also be undertaking DIY plastering - and thus will usually have appreciably less skill than a plasterer, and very probably much less concern about the state that their (probably very rarely used) trowel ends up in.

Kind Regards, John

A DIYer that does his own plastering will have a new or very seldom used trowel so it will be blunt, whereas a spreads trowel is nearly as sharp as a butchers knife and if on the odd occasion he hits the cable then it will take the cover off the cable no bother, we are of course talking about the same guys that plaster over the back boxes hiding them completely, also being thick skinned they're not about to tell you that they cut through your cable, if it fails that work is all in vain, strip it out and start again, I would never leave an exposed cable if the spread is about to start.

 

[JohnW2]

A DIYer that does his own plastering will have a new or very seldom used trowel so it will be blunt, whereas a spreads trowel is nearly as sharp as a butchers knife and if on the odd occasion he hits the cable then it will take the cover off the cable no bother...

The latter part of that is certainly true. As for the former, I think you may be underestimating how much damage some people manage to do with a not-broken-in fairly new trowel! Perhaps more to the point, a fair number of DIYers will be reading advice which is out there that they should sharpen a new trowel (with a stone or whatever) before use!

However, in context, I repeat what I said before - if one is talking about cables clipped to the bottom of chases of reasonable width and adequate depth, it would take an idiot of either a professional or amatuer plasterer to damage it. It's when one has cables on bare walls that issues can arise.

Kind Regards, John

 

[Chri5]

What's wrong with large headed nails hammered in the edge line so the head holds the capping? (And thus your not nailing through the capping and splitting in).

 

[sparkwright]

Exactly.

 

[OwainDIYer]

we are of course talking about the same guys that plaster over the back boxes hiding them completely, also being thick they're not about to tell you that they cut through your cable

I corrected that for you