Earthing external conduit

[Rockingit]

Got a not-very-interesting but mostly irksome problem just arisen on a new build -

Client has just decided that she needs an extra couple of outside lights down a wall, after the first fix was finished ages ago and just as the plasterers are packing away. But, the outside block wall has yet to be rendered so it's OK as I can just put some cable splits/extensions in and piggy-back off the cable already presented nicely through the wall to the first fix positions. Run the extra cable along in some steel conduit fixed to the wall, bury the whole lot in render and no-one will ever know.

The problem is that I only have the lighting circuit cpc (so that's the 1mm on a 1.5T&E) available to use for bonding the conduit. What do we reckon, peeps? Running new cable from inside is not an option. Circuit/s RCD protected.

 

[GLENNSPARK]

earth the conduit using the cpc from the existing cable....

 

[Engineer54]

Silly question now, ....Why do you need to use Metal conduit, why not plastic??

 

[GLENNSPARK]

i wa thinking that n all eng but as all he has is this 1.5mm cpc....better to use that and keep PD low.....

 

[GLENNSPARK]

lower..lol...

 

[Deleted member 26818]

Are you thinking, that this conduit will be an extraneous-conductive-part, and will require bonding?
It would only be such, if you bury it in the ground, and it then enters the property.
If you're just running along the wall, it will be an exposed-conductie-part, and just require earthing.

 

[Rockingit]

Reason for running it in steel is simply mechanical protection - where the cable run will end up is prime target for someone in the future to go drilling for hanging baskets etc on the outside wall and it's way off zone (if you can really make that case on outside walls). Yes, yes, I know, big wall and small target, what are the chances etc etc, but in my book you don't do half a job. My initial reaction was just to run it in some capping as it's being rendered over, but then I looked at the height on the wall and thought better of it.

 

[Rockingit]

Spin - I guess I'd have to class it as extraneous as it's going to be buried in the wall under render, hence my thinking that the cpc isn't going to cut it from the viewpoint of the regs.

 

[GLENNSPARK]

i was thinking you meant exposed rockin..hence post 2 mate....

 

[GLENNSPARK]

is there any way you can get a clamp on it and run a bonding conductor to it?....

 

[GLENNSPARK]

even though this conduit is being buried within render..the fact that it is acting as part of a containment system for an electrical installation would make it an exposed-conductive part though surely rockin?.....

 

[Rockingit]

is there any way you can get a clamp on it and run a bonding conductor to it?....

Not a chance!! Apart from the fact that the plasterers have just done a superb job and it's still drying, the building is all super-eco with a non penetrable vapour membrane in the walls, the house CU is about 20m away and the MET is in the pump house building next door!!

 

[GLENNSPARK]

its an exposed conductive part this rockin...

 

[GLENNSPARK]

test between it and existing bonding to confirm...

 

[Rockingit]

even though this conduit is being buried within render..the fact that it is acting as part of a containment system for an electrical installation would make it an exposed-conductive part though surely rockin?.....

TBH, the more I think about it, the more academic it becomes - I'm stuck with what I'm stuck with. It's not by design, and my concern is let's face it fairly belts and braces, so the cpc will have to do the job whether it's ideal or not and I'll make a note of it on the paperwork. Shame that it's only a 1mm, as with that much steel buried in the external wall I reckon it'd bring my Zs values right down!!!

 

[GLENNSPARK]

i`l admit here....i had to go away and mull it over as its a tricky one this......but i may be wrong here....all i can go with is the containment thing rockin and blank out of my mind the fact that`s buried in render...also, you only have the existing CPC to use.....so go for that.....

 

[Deleted member 26818]

Spin - I guess I'd have to class it as extraneous as it's going to be buried in the wall under render, hence my thinking that the cpc isn't going to cut it from the viewpoint of the regs.

Again, unless it is buried in the ground, and then enters the property, it is not extraneous.
You bury back boxes in plaster on the walls, do you bond them?
What are you like with Crittle windows?

 

[GLENNSPARK]

he`s right rockin matey.....you have a means of earthing this.....so thats your play here mate....

 

[Rockingit]

The way that this project is dragging on, I reckon it'll be me buried in the ground and my ghost entering the place to finish it off!!

But yes, point well made and taken. A non-exposed exposed conductive part it is, then.

 

[malcolmsanford]

Interesting note to this the BGB has changed the definition of an exposed conductive part from

"Conductive part of equipment which can be touched and which is not normally live, but can be come live when basic insulation fails"

to

"Conductive part of equipment which can be touched and which is not normally live, but can be come live under fault conditions"

For me that's poses an interesting question. how many of us have run say a T + E clipped surface but there is an area that we have considered it may have got damaged so inserted it into a length of steel conduit, simply for mechanical protection. Though I have never considered T+E Double Insulated, I have always considered the sheath to afford it better than basic protection and therefore never considered the need to earth the conduit.

Now that the definition as changed from when basic insulation fails to under fault conditions are we going to have to start earthing this length of conduit.