1) part winding 60:40 or 66:33 motors are used in european supermarkets for compressor motors above 7.5 kw . these motors can be started up without the use of compressor unloading mechanism ... example a start unloader like suction discharge by pass line .
2) 66:33 motors are better than 50:50 as these can take start up loads better . First 66% winding is switched on and within one second the balance 33% winding comes on via timer . This sort of start up also helps restrict the start current kick since only one winding ( part winding ) is put across the power . Both can be interlocked , that means if one winding trips , both windings should switch off to avoid motor operating on part winding .
3) Caution : do not switch on smaller part winding first . INDIVIDUAL WINDINGS NEED INDEPEDENT OVERLOAD RELAYS OF DISCREET RATING
4) Star delta motors start with 30% of power whereby compressors must be switched on with 100% unloaded start .