Presumably that is the same international standard rewritten as a local regulation.


So does BS7671 say it’s up to the DNO to keep their PME network earthing resistance down sufficiently lower that their consumers earthing via intended and unintended paths to earth through supplementary electrodes and extraneous-conductive parts in contact with the mass of earth?


Whereas the Irish Regulations tell you what the DNO/DSO needs to achieve?


 Andy Betteridge

1.  No LV net has both TT and TN* customers.  I'm not sure that's always the case in Germany, but I infer it's typical given that I've seen pages about a "network" (i.e. its customers!) all changing from one form to another: e.g.  TT-TN or TN-TT).  Imagine a DNO in the UK suddenly requiring that!

Certainly not the case in the UK. Even a single customer can present mix of TN and TT - e.g. my house is TN but the detached garage, connected to the same supply, is TT.


   - Andy.

Andy(J)

My assumption "1" about not mixing TN and TT in a network might have been unclear: I only meant that in some German networks it may be a good assumption that all customers use the same method.  The UK, I realise, leaves the customer to choose whether to use a provided earthing terminal, and so can have a mixture within a network or a single customer's installation. The UK DNOs certainly can't make this assumption unless they know they never provided any earthing terminals for customers on a network.


Andy(B)

I didn't immediately comment on your question, as I don't know the intentions of the 7671 committee in keeping 411.4.1 but not the note that went with it.  I assume there are others on this forum with a much better idea than I have.

Just reading the 411.4.1 that you posted as an image, its significance for the typical reader (I assume an electrician working with an installation most likely on a public network) seems to be that they can trust the provided earthing terminal, if its loop impedance is ok, without responsibility to consider the sorts of things mentioned in the 'NOTE' that started this thread. 

DNOs don't have the wiring regulations as the basis for design of their own networks, so there seems no point directing 411.4.1 at them.

Are there non-public TN-C-S systems in the UK, where the 'C' part of the network (with PEN) comes under the scope of the regulations? I'm not familiar with industrial/commercial practices in the UK, and would have guessed they would use TN-S when running a site with its own transformers. I know there are private TN-C-S systems in other countries, but the UK has historically been particularly 'protective' about multiple-earthing of load-current carrying conductors (telephone disturbance?), as well as about PENs (shock safety in the even of a break).