Bonding Conductors

YTSOxford · Nov 27, 2008

hi, am going to be running a new supply to a detached garage and am wanting to seperate the building from the main houses PME and have the garage on its own TT supply. The feed to the garage will come from a 32A breaker, RCD of course..... just wanted to know what csa earthing conductor you guys usualy run? Just getting my head in a mess reading the dam regs! Would you size it based on the conductor sizes of the armoured cable to the garage or still size it on the house supply??? Thanks all!

YTSOxford · Nov 29, 2008

I think i'll just be on the safe side and run a 16mm conductor to from the garge board to the rod.

andyb · Nov 29, 2008

The csa of the main protective conductor only needs to be the same size as the line conductor.

Though if it is buried it needs to be minimum 2.5mm sq if protected against mechanical damage or 16mm sq if not.

Spudnik · Nov 29, 2008

I think you will find it has to be at least half the size of the line conductor.

Otherwise we would have 25mm2 main earthing conductors to squeeze into a CU.

Therefore 32A 10mm supply, 6mm to your rod.

andyb · Nov 30, 2008

Jason, I think you are right for equipotential bonding. But I think for the main earth you need to look at table 54.7 which says that for line csa up to 16mm the protective conductor should be equal to this.
I agree that up to 35mm tails 16mm is adequate.

beaver74 · Nov 30, 2008

if you are going to t,t the garage then you dont need to worry about the size of cpc as you will only need to earth the armered and isolate the earth from garage earths via a pvc enclosure

just read properly earthing conductor 6mm if not buried

maddfridge · Nov 30, 2008

andyb said:
Jason, I think you are right for equipotential bonding. But I think for the main earth you need to look at table 54.7 which says that for line csa up to 16mm the protective conductor should be equal to this.
I agree that up to 35mm tails 16mm is adequate.

hi all

you colud use the adiabatic formula that will bring down the size of the conductor but practically a 16mmm will be more than enough just going through this at the moment for design course

need a beer

cheers

Spudnik · Dec 1, 2008

andyb said:
Jason, I think you are right for equipotential bonding. But I think for the main earth you need to look at table 54.7 which says that for line csa up to 16mm the protective conductor should be equal to this.
I agree that up to 35mm tails 16mm is adequate.

Andy, you are right.

Im not reading posts properly again!

I'll get me coat.

YTSOxford · Dec 1, 2008

hi again, thanks for all your inputs. I ran 16mm cos there is a reg that says, if it is not mechanically protected the earthing conductor should be 16mm. Which it isn't. its just clipped direct from the garage CU to the rod. The swa to the garage is earthed by the armour but no earth is brought to the garage; it is only connected at the house.