PME Mains on Private Networks - Wiring and the Regulations BS 7671 - IET EngX - IET EngX

PME Mains on Private Networks

Am I correct in thinking that on a large site with a private HV network (licence exempt distributor), they can use PME mains for the LV, designed to ENA standards and in compliance with ESQCR?

There seems to be a belief that ONLY a DNO can use PME mains.

Thanks in advance.

  • Anyone who's not a 'consumer' (who are prohibited from using CNE conductors in their installation Regulation 8(4) of ESQCR) could theoretically  use CNE conductors.

    Does the connection agreement provide a status?

    However, going forward, embedded generation and G98/G99 connectivity to the grid (whether at HV or LV) may well change the status of someone who thinks they are a 'generator' or 'distributor'. to a 'consumer' .. that might, again, depend on connection agreements.

  • 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


  • Many thanks for the reply - I had overlooked 8(4).

    I would have to dig the connection agreement out, but I doubt it would help in determining if the private network operator is a 'consumer' (from the connection agreements I am familiar with).

    Looking at the definition of 'consumer' within ESQCR, the network operator is not 'supplied' by a supplier - any electricity they consume comes from the tenant installations (small power and lighting for the substations), so hopely would not be a 'consumer'?

  • 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.


  • UCE has written a paper on this issue for a client. Please give me a call on 01226 610888.

  • UCE has written a paper on this issue for a client. Please give me a call on 01226 610888.

  • It's worth remembering that, if it's later planned for the site to include, at a later date, Solar PV, storage, etc., then there can be issues with ground currents if inverters are connected in the "TN-C" portion of a TN-C-S system, which can affect inverter operation/efficiency. (I haven't included V2X in there, because 722.312.2.1 not not permit EV charging to be supplied via a circuit with a PEN conductor, see below).

    With some technologies, DC protective conductor currents could be a concern also.

    If you are using BS 7671, there'd potentially be a need to iron out any conflicts between BS 7671 and ENA guidance (BS 7671 does not apply to systems for distribution to the public, other than prosumer's installations covered by Chapter 82, i.e. shared PEI).

    If you are supplying EV charging equipment, 722.312.2.2.1 might require some interpretation, as it's just 'a circuit' which could be a [any] distribution circuit as well as a final circuit. How you define 'installation' might be important, but equally if you are distributing with a system where BS 7671 applies, to an installation that has (or could reasonably be expected to have) EV charging equipment, would 722.312.2.1 apply (considering the wording of the Scope in 722.1)?

  • Hello, I think the test for consumer in this context would be the existence of a meter used for settlement and any installation downstream of such a meter would be a consumer installation.  The test for a settlement meter would be whether it has a full MPAN.  This can be established from the relevant DNO or IDNO MPAS enquiry service.

  • Cop2 Meters on the 33kV incomers to the site, everything downstream is private.

    Private meters on all the buildings the 11kV substations feed, as well as any services the LV network feeds.