A private supply is defined by BS 7671 as a supply that comes from a non-public source of energy. Therefore, the second option in your question is the correct one. A private supply can be produced by different types of generators, such as PV, diesel/gas/nuclear, or batteries. The first option in your question is not a private supply, because it still depends on the public grid supply at the HV level. The private transformer only changes the voltage level, not the source of energy.

AMK said:

A private supply is defined by BS 7671 as a supply that comes from a non-public source of energy.

BS 7671 certainly talks about private sources and private transformers - both not really directly relevant in terms of the particular issue we are discussing?

Where is "private supply" defined in the standard? (certainly not in Part 2).

Thanks, that's my thiughts as well. But do you know where this in the book this is defined? 

Apologies for the spelling, trying to watch the rugby and type at the same time. Do you know where this distinction is made?

Apologies for the spelling, trying to watch the rugby and type at the same time. Do you know where this distinction is made?