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]

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.

 

[Rockingit]

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

OK then...... so we can't touch it because it's buried (though I guess the argument would be made with a power drill!), so around in circles we go.... bond or earth?! Not that I'm going to be bonding it, regardless, but it's becoming an interesting discussion!

 

[i=p/u]

il say the back boxes cover this and it is rcd protected for bob the builder wanting to screw up some flowering baskets.... thats my easy awnser...

you guys are so more technical..

 

[Rockingit]

il say the back boxes cover this and it is rcd protected for bob the builder wanting to screw up some flowering baskets.... thats my easy awnser...

you guys are so more technical..

And that's exactly my practical solution as well!! But on a side issue, how many 'new' / DI blokes are earthing back boxes these days?!

 

[Engineer54]

Your thinking far too much into this!! You can't cover every single possibility of what might or might not happen in the future. Install these extra lights as you would anywhere else, that complies with BS7671 and move on. You'll give yourself ulcers worrying about stuff like this...lol!!!:rolleyes4::dizzy2:

 

[Rockingit]

What? Ulcers for a second time?? I thought after divorcing wife number one and a lifetime of 24hr boozing that I couldn't get any more??!

 

[GLENNSPARK]

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.

as you say here malc....the sheath of a T&W is not considered insulation....its there to protect the insulation (core colours)....and provide some protection against abrasion......its the cpc which together with a low Zs (disconnection times) will provide fault protection for this cable......and the fact that rockin stated that an RCD was being used to provide additional protection for this circuit.....seems to me like the conduit is a bit unnecessary anyway...but as its there.....earth it....

 

[BillyTheSparks]

But on a side issue, how many 'new' / DI blokes are earthing back boxes these days?!

Me, Personally. Always.