As far as I can tell, it is not defined anywhere that can be considered legally binding.

The general consensus is that it is clear cut for privately owned gensets and transformers, and far less clear with DNO owned transformers with a single user wired as TNS or PNB.

Mike

In the UK, the public supply is one to which the Electricity Safety, Quality and Continuity Regulations 2002 (an amended) [ESQCR] apply. (In Northern Ireland, there is a later dated "NI" version of the Regulations.)

"Distribution networks within the scope of the ESQCR" is what is intended when BS 7671 talks about "systems for distribution of electricity to the public", and also similar statements in guidance on the application of BS 7671.

mapj1 said:

As far as I can tell, it is not defined anywhere that can be considered legally binding.

In one way that's true even of ESQCR, in that it's the "network" and "consumer" that are key considerations for interpretation in ESQCR.

But I suppose that's not the end of things at least on the surface, and some cases might require a bit of further "mental digging" before you come to the conclusion that ESQCR is the answer. For example:

• What about where a Consumer's Premises has more than one Tenant? The distribution network stops at the relevant meter for which bills are levied for the supply (although the meter belongs to the meter operator, which is usually not the DNO or IDNO). However, even when more than one tenant is supplied from a single meter (and there may be "landlord's meters"), the tenants' installations are still classed as being connected to the public supply.
• Some sites receive their power from the public supply at HV not LV. The site will have a private LV distribution network but is still classed as being connected to a public supply.
• Some sites have their own backup generators ... like hospitals, or some of the newer domestic installations with Solar PV and storage batteries that have an "island mode" supply. In this case, the installation is still classed as having a public supply, but there are specific Regulations 21 and 22 of ESQCR that cover private generation operating in parallel with, or as a switched alternative to, the public distribution network (and it doesn't again matter whether the supply is received at HV or LV).

In general (perhaps excepting railways and similar where ESQCR is limited as discussed in the Regulations), only sites that have no connection at HV or LV to the public distribution network ("grid") are classed as having "private supplies".

Thank you very much

Thank you very much..