A site with private transformers will have parts of the installation that are equivalent to the DNO's LV network, and other bits that are the equivalent of the consumer  side. It may not be sensible to  use the metering as the demarcation point between distribution and consumption as you would for wiring in the street.

In practice on a big site, at least where there are multiple transformers with parallel secondaries that may be independently switched, there have to be multiple N-E bonds and even if not done like the DNO as the full 3 cores 3 phase PEN armour, the link between the NE bonds has to be judged as 'not consumer' for the purposes of ESQCR.

The demarcation beyond which N and E are split, never to join again,  is then made at the main panel/ breaker

Mike.

Thanks Mike - that makes sense. So you think Wv DNO type cable in my scenario above would comply, as long as there is a clear point beyond where the N&E shall never meet?

Sounds OK, only so long as there is no 'consumption' of power on the CNE side of things. However, I would not expect any combined NE to be more than the hop between the transformer(s) and very first breaker or big fuses. The site NE bond(s) may be at or near that breaker, rather than at the transformer. These things are not always clear cut. And for the final answer, check with the DNO, as in the end they are connecting HV to the thing, and as Graham says, really it hinges on who signed up for what.

M.

Sounds OK, only so long as there is no 'consumption' of power on the CNE side of things. However, I would not expect any combined NE to be more than the hop between the transformer(s) and very first breaker or big fuses. The site NE bond(s) may be at or near that breaker, rather than at the transformer. These things are not always clear cut. And for the final answer, check with the DNO, as in the end they are connecting HV to the thing, and as Graham says, really it hinges on who signed up for what.

M.