earthing advice

[Guest111]

Hi all,just after a few thoughts on this one been to look at the place I used to work at and they are having a new building put up,I had to straighten out the wiring last time after the previous spark had made a b of it and had not bonded the steelwork which I did.Now they are having a new shed put up,concrete panels and steel beams next to the existing one,you can stand between the 2 and touch both sets of steelwork so the question is do you tt second building or do you bond back to main earth in first building? I know the regs about not exporting pme but it concerns me if someone were to touch both sets of steel at same time could there be a difference in potential between the 2? the supply is a tncs system 3 phase.seems funny asking for advice on this as I am usually advising others but just thought I,d run it by you guys.nice little job to do in my retirement lol.

 

[telectrix]

I know the regs about not exporting pme;


it's not a caravan or a boat. PME the damn thing. same potential on both buildings.

 

[Richard Burns]

Agree^^^
Same supply, bond second building back to main building, safe as houses?!

 

[sedgy34]

agreed same potential has to be aknowledged

 

[Guest123]

If you have a suitably sized sub-main from the existing to the new building, the CPC of the sub could then be used as the circuit CPC and also the protective bonding conductor

This means you could then use the earthing terminal of the new bulding as a BEMT so all extraneous conductive parts would only require bonding to this terminal rather than back to the MET in the existing building.

 

[Guest111]

Cheers lads that was exactly my thoughts but a second opinion always helps,running a 50mm 4 core and have some 25mm g/y so that should do nicely

 

[telectrix]

watch the pikeys don't see it before you've been paid.

 

[Engineer54]

When you say ''concrete panels and steel beams'' do you mean concrete panels fitting into vertical H frame steelwork that's either bolted or set into the concrete slab/base??

If set into a slab/base with a steel re-bar grid etc then the chances are you will also be adding another earthing electrode to the PME supply via a Ufer earth. Which is never a bad thing to do on such installations....

Even when these strochons are bolted to the slab/base, there's a good chance of hitting the re-bar, and achieving a similar effect. Check the steelwork first to see if it is extraneous, ...mind i would be surprised if it wasn't... lol!!!

 

[Guest111]

When you say ''concrete panels and steel beams'' do you mean concrete panels fitting into vertical H frame steelwork that's either bolted or set into the concrete slab/base??

If set into a slab/base with a steel re-bar grid etc then the chances are you will also be adding another earthing electrode to the PME supply via a Ufer earth. Which is never a bad thing to do on such installations....

Even when these strochons are bolted to the slab/base, there's a good chance of hitting the re-bar, and achieving a similar effect. Check the steelwork first to see if it is extraneous, ...mind i would be surprised if it wasn't... lol!!!

what happens is concrete pads are poured and the steelwork bolted to them,the steel frame is erected and concrete panels placed in between them then a mesh rebar frame is placed inside the building and concrete poured over the top.

 

[Engineer54]

what happens is concrete pads are poured and the steelwork bolted to them,the steel frame is erected and concrete panels placed in between them then a mesh rebar frame is placed inside the building and concrete poured over the top.

OK with you... lol!!

Well if your around when they lay down the mesh before they pour over it, take a connection or two from the mesh to the bolted steelwork at at least 2 locations (say at diagonally opposed corners) and another directly from the mesh to the EMT. ...And the jobs a good-un...lol!!

 

[Guest111]

OK with you... lol!!

Well if your around when they lay down the mesh before they pour over it, take a connection or two from the mesh to the bolted steelwork at at least 2 locations (say at diagonally opposed corners) and another directly from the mesh to the EMT. ...And the jobs a good-un...lol!!

mesh and pour done, right lash up by all accounts havent tied the mesh sheets together just put them in and done the pour,as i said a right mess,gonna wear my ballistic vest when i go down,dont fancy copping an arrow if the indians turn up as it seems we,ve already had the cowboys,lol

 

[Guest123]

The other thing that springs to mind now that you have stated you are running a 4 core for I'm assuming a TP&N supply is that you will be relying on the armour of the SWA to act as your bonding conductor for the extraneous conductive parts in the new building.

Before I go any further, can you clarify wether or not the 25mm earthing conductor you mention will be run out to the new building from the existing building along with the SWA or is it just going to be used for protective bonding purposes in the new building???

 

[Guest111]

The other thing that springs to mind now that you have stated you are running a 4 core for I'm assuming a TP&N supply is that you will be relying on the armour of the SWA to act as your bonding conductor for the extraneous conductive parts in the new building.

Before I go any further, can you clarify wether or not the 25mm earthing conductor you mention will be run out to the new building from the existing building along with the SWA or is it just going to be used for protective bonding purposes in the new building???

25mm from met in main building to sub board in 2nd building then a 25mm from sub to steelwork.

 

[Guest123]

25mm from met in main building to sub board in 2nd building then a 25mm from sub to steelwork.

Thats fair enough then.

Issues can arise arise when diverted neutral currents travel through the armour of an SWA when used as a bonding conductor, under fault conditions due to the heat that can develop in the armour affecting the inner cores.