Phase rotation was such an issue with IBM that they gave the CEs a jumper in the power tub to swap them. Before that it was always swapping them at the easiest place to get at it. The odds of the recepticle being right was pretty much 50:50. Part of the problem was whether it was clockwise at the face of the Russell Stoll plug or the receptacle.
Joe I have done it many times like you say with the scope but usually we just plugged stuff in and saw which way the fans ran.
