That's old European designation. I believe the terminals of a motor leading directly to the windings were/are XYZ, the terminals fot the feeder are UVW, and going backwards in the alphabet, the terminals inside receptacles et cetera were named RST. Has been L1, L2 and L3 for some 20 years though, at least in Continental Europe. My school (built in 1975-1980) still has the old designations written everywhere. After all, it still has fuses instead of breakers too...
