It's an oboselete European standard that was used in a very similar way to 120V in the US.
So was this same configuration of plug/socket used in Europe on 127V + 0 before obsolescence? I have likewise been trying to establish what plugs were used in the British Isles when the, now long-gone,110-0-110V DC systems were in vogue. Was a 110V supply ever tapped in this system?
