Discuss Out building earth in the Electricians' Talk area at ElectriciansForums.net
I take it then Malcolm that you do not accept that you should first contact the DNO before exporting a TN-C-S earth, and that you would be quite suprised if they were to disconnect your supply, or just remove the PME connection after discovering that youhad exported such an earth without their permission?
This states that the main earthing terminal shall be connected with earth by one of the methods described etc.Sorry. 542.1.1
This mentions you can connect to one of the types of earthing system.
here we go again!!!
I have never,ever heard of the DNO getting uppity over a TNCS earth exported to an outbuilding,and I have never contacted them before doing so....In my experience all they are interested in is a cert saying it complies with bs 7671.
Simplified....
1.There are no regulations in Bs 7671 preventing a TNCS earth being used as the earthing system for an outbuilding..(except in some special locations as defined in bs 7671)
2.If there are extraneous conductive parts within the outbuilding that require main bonding then the requirements for bonding TNCS installations apply. This would mean a minimum 10mm bonding conductor would have to be installed from the outbuilding back to the MET. This may be impractical or it may not be cost effective.It may be cheaper to separate the TNCS earth and install a rod,in which case main bonding can run to the outbuilding DB.
3.If there are no extraneous conductive parts within the outbuilding requiring main bonding using the TNCS earth is in full compliance with bs 7671. As long as you carry out and cert the install to bs 7671 there is no need to contact the DNO.
That is how I've been doing it for 30yrs,and that is in full compliance with all relevant regulations.
If you are not in agreement....well, do it your own way
This was the guidance we were given many years ago for installing street furniture.
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