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Sorry if this has been covered before. Went to a job today to wire a heating system and the install requires main bonding. The problem is that I can't get to the main board as its solid floors etc. There is a sub main feeding a db upstairs supplied by a 16mm twin. Can I run my 10mm earths to this sub board
? TNC-S earthing. Please be gentle!!
 
If its 16mm twin and earth then i would say no as the earth is not a large enough conductor size to be used as a combined earthing and bonding conductor back to the met

Tim
 
Need to wire a supply for heating and an immersion. Will be replacing the main db and various other works so will need to wire main bonders. Place is a bit of a shambles to be fair... No cpc's in downstairs lights , exposed parts in db's etc, might end up being there a while!
 
Need to wire a supply for heating and an immersion. Will be replacing the main db and various other works so will need to wire main bonders. Place is a bit of a shambles to be fair... No cpc's in downstairs lights , exposed parts in db's etc, might end up being there a while!

I'd say as it's a bit more than just wiring the heating system you should be ensuring all bonding meets current regulations along with all other work you undertake. IMO
 
There is something on the ESC website re being able to use 6mm as long as there are no signs of thermal damage etc etc. However IMO you are installing new circuits and replacing a DB so I would be looking at installing a new main earth and bonding conductors as per table 54 (7 or 8) can't remember due to it being TNC-S. So if the DNO neutral is 35 mm or less then Im afraid its going to have to be 10mm !! I take it there is extraneous parts where you are doing the work!
 
Last edited:
There is something on the ESC website re being able to use 6mm as long as there are no signs of thermal damage etc etc. However IMO you are installing new circuits and replacing a DB so I would be looking at installing a new main earth and bonding conductors as per table 54 (7 or 8) can't remember due to it being TNC-S. So if the DNO neutral is 35 mm or less then Im afraid its going to have to be 10mm !! I take it there is extraneous parts where you are doing the work!

Think you'll find that only refers to leaving ''Existing'' 6mm main bonding cables in place, not that you can install 6mm MB cables where it calls for 10mm...
 

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