Interesting -- So BS546 and BS1363 were once used in New Zealand then?

That middle image showing a ring looked very familiar and sent me running to the book shelves. I have open in front of me the A.S.E.E. (Association of Supervising Electrical Engineers) Guide to the I.E.E. Wiring Regulations 13th Edition, 1955, as amended to December 1963. There is a diagram illustrating the ring circuit which is so similar to yours that they must have a common origin.

The only big difference is that the ASEE version shows the earth running separately at the source instead of being bonded to neutral at the panel, which of course is how the circuit would have been wired here.

The labeling has obviously been re-done, but is otherwise very similar, and specifies 7/.029 cable, which was also standard for rings here.

I don't have a functional scanner here at the moment, or I'd post my version. I'll add the image when I get the chance.

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For a start, everything is in Imperial measurements,
Nothing strange about that. The IEE here was a relatively early adopter of metric, and they didn't switch over until about 1970.

What about the "2-pin T" and "2-pin parallel" outlets? Have you ever come across them? They look suspiciously like NEMA 1-15 and 1-20 receptacle configurations.

Oh, just one last observation..... Your NZSS 1125 outlet is upside down! [Linked Image]