1. Contactor A contactor is a relay with heavy-duty contacts to carry large amounts of current. Available either Normally Open or Normally Closed

2. Full-Voltage Starting Line TerminalsMotor Terminals Contactors S1, S2, S3 T1 T3 T2

3. Autotransformer Starting

4. Autotransformer Starting (continued) To Start –All S contacts CLOSE –Line terminals connect to high-side of autotransformers. Low-sides of autotransformers are connected together. Taps of autotransformers are connected to the motor terminals providing lower than line voltage for starting.

5. Autotransformer Starting (continued) When motor reaches near-rated speed, S contacts are OPENed and the R contacts are CLOSED. Full voltage is now applied to the motor terminals.

6. Series Impedance Starting

7. Close S contacts at Start Open S contacts and close R contacts at Run Apply approximately 70% of rated voltage to start Z is usually either Inductive or Resistive