3-phase Motor Starting Method by Automatic star-delta starter Operation and Working Principle of Automatic Star Delta Starter: From L1 The phase current flows to thermal overload contact through Fuse, then OFF Push button, On Push button Interlocking Contact 2, and then C3. This way, the circuit is completed, as a result; Contactor coil C3 and Timer coil (I1) is energized at once and the motor winding then connected in Star. When C3 is energized, its auxiliary open links will be closed and ....