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I am having a debate about the requirements of earthing in an HMO -
The incoming supply is 3ph 200amp and Gas and Water are bonded 50mm as needed in this case.
The building is one block with its internals divided into 20 flats, each flat has its own distribution board rcd protection split-board, the supply to the flats comes from a local sub mains via a 16mm T&E, this does not have rcd cover as it does not route anywhere along its install where it would require the need for rcd protection.
The flats have a common plumbed in central heating system in metal pipework and no gas fixtures.
The discussion or debate is that the T&E requires an additional 10mm earth cable to run with it but I disagree, as there is no individual bonding requirement for the flats from the flat DB, I came to this conclusion because it is 1 common supply to the building and that has been bonded as needed at source.
Earth Loop Impedance for the 16mm T&E and as long as the ELI is met then there is no additional 10mm needed for the flat supply.
In my view the cable earth is good enough as it satisfies the adiabatic equation but he has contacted his own scheme providers and they say it needs the 10mm running with it.
Now either I am missing something here or Nappit are pushing out the wrong advice to this guy... as my field is machinery control and design I am a little lacking in this area now and just need my conclusion verifying or correcting... feedback appreciated.
I think I have included all the info needed.
The incoming supply is 3ph 200amp and Gas and Water are bonded 50mm as needed in this case.
The building is one block with its internals divided into 20 flats, each flat has its own distribution board rcd protection split-board, the supply to the flats comes from a local sub mains via a 16mm T&E, this does not have rcd cover as it does not route anywhere along its install where it would require the need for rcd protection.
The flats have a common plumbed in central heating system in metal pipework and no gas fixtures.
The discussion or debate is that the T&E requires an additional 10mm earth cable to run with it but I disagree, as there is no individual bonding requirement for the flats from the flat DB, I came to this conclusion because it is 1 common supply to the building and that has been bonded as needed at source.
Earth Loop Impedance for the 16mm T&E and as long as the ELI is met then there is no additional 10mm needed for the flat supply.
In my view the cable earth is good enough as it satisfies the adiabatic equation but he has contacted his own scheme providers and they say it needs the 10mm running with it.
Now either I am missing something here or Nappit are pushing out the wrong advice to this guy... as my field is machinery control and design I am a little lacking in this area now and just need my conclusion verifying or correcting... feedback appreciated.
I think I have included all the info needed.