6mm main earth

[Rutts35]

Following on from my cable I'd question. Same property. Landlord has agreed to replacing the CU. However the main earth is 6mm. 80a head, PME supply, 16mm tails. Earth is fine by the adiabatic and has no signs of over heating. Supplying a CU that is in a small two bed flat with 4 circuits. 40a shower, 32a scoots, 6a lights and 20a cooker. Problem is that the meter cupboard is in the communal hallway and CU is in a cupboard in the flat. It's across the hallway in the flat, not directly behind it. It will be an absolute ball ache if I can't pull it in as is. If I can't attach to the existing earth and pull in a new 10mm can it be left when I replace the CU? I think I know the answer but I'm hoping one of my learned colleagues will say it's OK as is.  ray   :innocent

 

[Evans Electric]

I see your problem Rutts...... but as far as I know  your earth needs to be half the size of conductors  ... hence  16mm for 25mm tails    ..so 16mm tails would need   "8" mm  earth  which would be 10mm .    However thats a rule of thumb , perhaps the adiabatic  overrules that .    

 

[Murdoch]

I see your problem Rutts...... but as far as I know  your earth needs to be half the size of conductors  ... hence  16mm for 25mm tails    ..so 16mm tails would need   "8" mm  earth  which would be 10mm .    However thats a rule of thumb , perhaps the adiabatic  overrules that .    

Not sure you can use the adiabatic with PME

 

[Evans Electric]

I think you're right . 

 

[Phoenix]

Not sure you can use the adiabatic with PME

Its not so much that you cant't use it, its just that *if* the conductor forms part of the bonding path then table 54.8 needs to be considered as well and likely that would increase the conductor size over what the adiabatic says is needed as as a CPC, but you might still get smaller than people think has to be commonly installed, i.e. you could end up with 25mm tails and 10mm earth and be fully compliant in most domestics.

I beleive the best practice guide now says that undersized bonding should not be coded providing a mimimum of 6mm and no thermal damage, not sure I'd agree, I'd generally go C3, but either way it wouldn't make it unsatsifactory, I think for a board change as its not something that would make the installation unsatisfactory then I'd be tempted to go ahead and note it as a comment on the existing

OP,

I am assuming the bonding goes to the board, rather than a terminal in the service cupboard, although it was not explicty stated?

How do the W/G servcies arrive in the building, separate feeds from teh street, or one main that branches off, is the main bonded where it first arrives in building?

Can you see how the electrical services are installed, is it CNE right upto your service head? or just CNE upto the ryefield board and then SNE out to each position, both technically TNCS*, but the later does a lot to stop circulating currents within the servcies within the building

*Though if its presented to you as SNE, you might not know it!

 

[Murdoch]

I believe the best practice guide now says that undersized bonding should not be coded providing a minimum of 6 mm and no thermal damage, not sure I'd agree, I'd generally go C3, but either way it wouldn't make it unsatisfactory, I think for a board change as its not something that would make the installation unsatisfactory then I'd be tempted to go ahead and note it as a comment on the existing

Which I would agree with 100% but is't the OP talking about the main earth conductor?

 

[Phoenix]

Which I would agree with 100% but is't the OP talking about the main earth conductor?

He is, but in terms of the main earth conductor to meet the requirements of being a bonding conductor on a TN-C-S, he has already assessed its capability to act as a CPC using the adiabatic and found it to be sufficient (if it was calaculated insufficent then that would be C2 on an EICR).

 

[Rutts35]

Yeah, the bonding doesn't go back the head. It goes back the board. Just l'n + e to the cu. Gas and water go back to here. So, yeah the main earth is just that. It's a pme head so cne up to head then sne out to board. I think I'm going to try and see if it will pull in, if not just note is on the cert.