I've been speaking with the local DNO with regard supply parameters to a single retail unit being converted into 4. The current supply being a 100kVA 3 Phase and neutral supply currently supplied via a 95mm2 3 core wavecon cable. In their opinion improvements could be made to the safety of supply given a loss of the neutral connection. TT being one, but possible difficult to achieve in the centre of a town in term of getting a low enough earth connection to have a larger up front RCD to achieve subsequent selectivity. The second being, as I understand it to effectively take the TN-C-S connection out into the road to the PME network and provide a 4 core wavecon cable to the building intake possibly a fake TN-S. I can understand that two connections are possibly better one, but ultimately still TN-C-S. Can they guarantee their connection is more reliable in ground rather than in the building. What happens to sizing of the main bonding conductor ? It's quite possible I've misunderstood what they are proposing. Does neutral loss more commonly happen to one build or multiple buildings ? Looking to understand what is being proposed.
If the system the TN-S cable is connected to is PME, then in general PME conditions may still apply, because you may get diverted neutral currents from other installations close by down your main earthing and bonding conductors.
There may be some things you don't need to worry about quite as much - such as Section 717 or Section 722 installations, but the example you cite, of size of protective conductors, is quite possibly still an issue.
So, I guess it all depends what's going on with the distribution network around your installation, and the DNO is the best person to ask about that.
Thanks for the reply. Perhaps there is a bigger issue with PME distribution generally. I wonder if configuration would be any with single phase EV charge points.
