Old 3 ph plugs were a greenish grey or light grey, flat 4 pole type, with equally sized but differently spaced pins. These are most likely to be encountered on old farms and in old workshops. Maybe I can take some pictures and post them.
Then we also had light-duty 3ph plugs with 4 round pins (like on a Schuko plug) in a square and a rectangular ground pin in the middle, widely used in small commercial environments (shops, supermarkets,...)
BTW, does anyone know where a plug with pins like a US 220V plug, but a little narrower and longer and a round ground pin could come from?
