The current configuration used in Australia, New Zealand, quite a few island nations of these two countries and also Argentina (that uses the same configuration, but it is inverted), was actually designed in Australia.
Just to clarify this, the Australian plug is an obsolete U.S design; so old in fact it has no NEMA classification.
Apparently, it wasn't popular in the U.S because of incompatibility with the parallel pin plugs, hence it died out with NEMA 5-15 replacing it.
The Australian Standard version from 1937 has slightly shorter pins, with the earth pin slightly longer than the live and neutral (for obvious safety reasons). In practice this makes no difference and the plugs and sockets can be used with one another. I have a pre 1937 plug with all long pins; it fits perfectly in the modern socket.
Prior to 1937, Australia was using British round pin plugs ,the bayonet light socket, as well as the non earthed (NEMA 1-15) and the nameless 3 flat pin American designs. Clipsal still make the 2 flat parallel pin plug rated at 250V, not that it has been used in domestic applications for very long time. The ease of making flat pins as compared to round ones with the machines we had is why the American design was ultimately adopted here.
Literature I've seen indicates that NZ continued with British configurations for somewhat longer than AU did. I'd be interested to know more on NZ's adoption of the plug; was it just the "de facto 7th state of Oz" effect? Was it officially adopted at the same or a later time?
It is interesting to note that although our wall boxes and plug pattern are of American design, the wiring colour code, fuses, and light sockets stayed with British practice.
Argentina would most likely have taken the design from the U.S directly without any influence from Australia; especially given phase and neutral are reversed. It would be interesting to know how the sockets were wired in the U.S. and which adoptive country kept to the original standard. Given NEMA 5-15's pins are connected in the same order as ours, I suspect Argentina is the odd one out.
I would be interested to know how China came to use it, and when it started doing so. The Chinese power leads I've got have the cable leaving the side entry plug on the top side when plugged into an AU/NZ socket and the writing is upside down. They use the same connections.
