And in requiring that the TN-C-S earth be "exported" to an outbuilding and an additional earth electrode provided at said outbuilding. There just isn't the same range of earthing options for the main building and auxiliary buildings as exists in the U.K., although until very recently there was one variation for feeding an outbuilding which would not be acceptable in Britain.From what we've been told, the Americans appear to have worked this out already - by demanding (rather than 'forbidding') an earth electrode to be connected to the incoming TN-C-S earth
That diagram is misleading, since no-one has suggested that the TN-C-S earth should be literally connected to the earth electrode, so that it's path to the (other) extraneous-c-ps went though the electrode's conductor. The actual situation (and 'choice/decision') I'm talking about is:<a diagram>
CNE on the consumer's side?until very recently there was one variation for feeding an outbuilding which would not be acceptable in Britain.
The situation I have been taking about is when the csa is inadequate - the reason for TTing it.The conductor from the TN-C-S earth to the 'real' extraneous-c-pc in the outbuilding either is, or is not, of adequate CSA as a boinding conductor for those parts.
I'm lost.Either way, whether one also connects the local earth electrode to the 'local MET' is, AFAICS, neither here nor there.
There is a significant difference since, as I said, your diagram had path from the incoming TN-C-S earth to the (other) parts it was meant to be bonding went via the earth rods conductor (which, as I said, electrically speaking could be as small as 1mm²).I do not see the difference in the diagrams.
If the CSA of the connection to the (very low impedance) extraneous CPs in the outbuilding were inadequate, one would have to abandon it and TT the outbuilding instead of using the TN-C-S earth at all, since there would otherwise be a theoretical risk of that cable becoming seriously overloaded as a a result of (extremely rare) very high fault currents. Adding a TT electrode as well as retaining use of of the TN-C-S would not significantly (virtually not at all) reduce that risk.The situation I have been taking about is when the csa is inadequate - the reason for TTing it.The conductor from the TN-C-S earth to the 'real' extraneous-c-pc in the outbuilding either is, or is not, of adequate CSA as a boinding conductor for those parts.
As above, to use an exported TN-C-S earth with an inadequate CSA conductor to bond 'very low impedance' extraneous-c-ps is theoretically 'not safe', and adding a connection to a local earth rod would make that situation neither more safe nor less safe (aka "neither here nor there").I'm lost.Either way, whether one also connects the local earth electrode to the 'local MET' is, AFAICS, neither here nor there.
Yes, combined on the feeder to the outbuilding, where the neutral and ground busbars at the outbuilding's distribution panel are bonded together and to extraneous parts as usual, and connected to the required local earth rod.CNE on the consumer's side?
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