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The "T" configuration outlet is officially used in Australia for extra low voltage applications (<32V) and has become very popular in recent years for 12V use in boats, caravans etc. However, its original use in Australia was for 32V DC farm lighting plants. Only a few days ago I found an article in a 1920's issue of the U.S magazine "Popular Mechanics" showing its use for the same thing. Readers were advised to use it so as to maintain correct polarity for the radio plugged into the outlet. Again, another U.S socket adopted by Australia.
