After a couple of bonding conductor questions I had I've started a new post for this so it's more specific.
I have a TN-C-S installation, at least 70mm line and neutral at the incomer, feeding a main distribution board which feeds 8 x 3 phase boards around a site. We are installing a 16mm SWA from this dis board to a new 3 phase board in a new building. Using the armour sheath as main earth for this board.
I have decided after my other post that the main bonding for gas and electric entering the new building will be run as a single separate continuous cable and tied to the SWA, but I am having a problem sizing it up.
First question is to check that the bond for these 2 services does need linking all the way back to the MET at the origin in the main building 50m away, and not just to the main earth in the new board in the new building (1m away).
If I went by the book it seems I should be going by the size of the incoming neutral of the supply in the main building, and the 16mm feed we're putting in seems irrelevant. So if our neutral at the supply is 70mm, we'd end up running a 25mm bond alongside our new 16mm feed. Seems over the top.
You can see my confusion - the board and feed that's going in is a separate building with this feed from the main building. In essence the new building is it's own equipotential zone and it makes more sense to me to bond the services in there to the MET in there, and not link back to the MET at the origin in another building.
Could someone please clarify this for me as it's driving me nuts, it's such a simple setup but I'm obviously missing the trick here. I've drawn a pretty picture too!
![[ElectriciansForums.net] Sizing bonding for subboard](https://electricians.s3.eu-west-1.amazonaws.com/data/attachments/1/1494-da8be8b8c9fb833bce5ab2f53961f5ed.jpg "[ElectriciansForums.net] Sizing bonding for subboard")
I have a TN-C-S installation, at least 70mm line and neutral at the incomer, feeding a main distribution board which feeds 8 x 3 phase boards around a site. We are installing a 16mm SWA from this dis board to a new 3 phase board in a new building. Using the armour sheath as main earth for this board.
I have decided after my other post that the main bonding for gas and electric entering the new building will be run as a single separate continuous cable and tied to the SWA, but I am having a problem sizing it up.
First question is to check that the bond for these 2 services does need linking all the way back to the MET at the origin in the main building 50m away, and not just to the main earth in the new board in the new building (1m away).
If I went by the book it seems I should be going by the size of the incoming neutral of the supply in the main building, and the 16mm feed we're putting in seems irrelevant. So if our neutral at the supply is 70mm, we'd end up running a 25mm bond alongside our new 16mm feed. Seems over the top.
You can see my confusion - the board and feed that's going in is a separate building with this feed from the main building. In essence the new building is it's own equipotential zone and it makes more sense to me to bond the services in there to the MET in there, and not link back to the MET at the origin in another building.
Could someone please clarify this for me as it's driving me nuts, it's such a simple setup but I'm obviously missing the trick here. I've drawn a pretty picture too!
