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!!!