[Arran]

Mike;
 A weird thing is that some older outlets were polarized, but I never saw a polarized plug on any device until the 1980s, and that included extension cords. The strange part is that I often see them on devices where a polarized plug would make no difference, like in double insulated things like hair dryers. I think that the theory may have been that if something needed to be polarized then they would put a ground on it as well. 
Regards
Arran