RCBOs, earthed metal conduit

[Donkmeister]

Never read technical docs after drinking...

Looking at my 17th edition on-site guide, p24, section c, I've noticed that RCBO-protected final circuits "usually" need to be installed in earthed metal conduit or wired with earthed metal-sheathed cables.

Looking at the 17th edition itself (522.6.6), it sounds like earthed galvanised capping would be sufficient.

Anyone got any thoughts on this? If a cable is buried in a plastered wall, is earthed metal capping sufficient protection for the cable, or should I really encase everything in conduit.

 

[sparkyspike]

Read 522.6.6 (v).

 

[Adam_151]

I want some of what you're drinking

Go on,,, read the section of the OSG you quote again...

 

[sparkyspike]

Never read technical docs after donking...

 

[ColJack]

and no, earthed galv capping is not sufficient.. it needs to be conduit or trunking.. it needs to surround the cable, not just cover it..

it is likewise not suitable for mechanical protection as it is not thick enough to prevent penetration by screws or nails..

 

[sparkyspike]

and no, earthed galv capping is not sufficient

It is if you comply with 522.6.6 (v)

Anyway, the OP misread his OSG...

 

[ColJack]

to comply with 522.6.6, you could sticky tape the cables to the wall and it would comply.. it still doesn't remove the requirement to RCD protect if less than 50mm from the surface..

glavanised capping is there for no other reasons than to keep the cable in place, make it marginally possible to re-wire at a later date, and to make life easier for the plasterers.. it's a lot easier for them if their trowel isn't skipping over a cable clip every 500mm or so..
it provides marginal protection against over zealous and under experienced plasterers who may catch a cable with the edge of a trowel if they don't realise it's there.. ( though many spreads will swear blind that none of them have ever caught a cable.... we know different.. )

 

[Click-Sure]

If its sticky-taped to the wall then it is exempt from the 50mm rcd protection rule, same as if it was in surface mounted pvc trunking, would struggle ticking the 'erection methods' box though...

I've moved over to LSF now in any case, much much more durable than regular grey pvc/pvc twin and earth. I can feel a new thread coming on...

 

[ColJack]

If its sticky-taped to the wall then it is exempt from the 50mm rcd protection rule, same as if it was in surface mounted pvc trunking, would struggle ticking the 'erection methods' box though...

you basing that on a re-wire?
on a new build first fix, before the plasterer has been in was the scenario I was refering to.. cliped / taped to the breeze blocks..

I've moved over to LSF now in any case, much much more durable than regular grey pvc/pvc twin and earth. I can feel a new thread coming on...

and twice the price isn't it?

what chart do you use for LSF then? it's not 4D5A as it's not PVC/PVC cable is it?

 

[Click-Sure]

Not twice the price, about 25% more at CEF.

When designing a circuit where I will be using it I use the same tables as I would use for PVC/PVC, verified this with my competant persons scheme. I can see where you are coming from though,

 

[ColJack]

screwfix ( the place a customer may go to check prices against ) is £37 for a 100m roll of 2.5mm² T+E.
£66.56 for the same roll in LSF..
so while not exactly twice the price, it's close enough..

 

[Click-Sure]

True, but I get enough for installing the materials, I don't mind not earning out of the materials. I am surprised screw-you-fix charge so much extra.

 

[Spark123]

Table 4D5A doesn't exist anymore - table 4D5 does.
This is for 70ºC thermoplastic insulated and sheathed flat cables with a protective conductor.
Also I don't see the need to put an already RCD protected (by an RCBO) cable inside any sort of metalic protection i.e. conduit, trunking or the likes even when concealed in a wall as long as it is in the correct zones.

 

[Click-Sure]

Un-earthed Metallic cable capping is just an EMI risk, I'll only use it if specified. If the plasterer damages a cable then its up to him/her to compensate the parties involved what it comes to rectifying the damage. Simple as.

 

[Spark123]

I can hear the plasterers tyres screatching from here