🔍 Key Concepts

• Wye (star) vs delta connection of a three-phase motor and which one is normally used for starting vs running • Difference between open transition and closed transition reduced-voltage starters • How contactors M, S1, and S2 and the resistors R route power to the motor during start and during run

💭 Think About

• Trace the power path from L1, L2, L3 to the motor terminals during the initial start condition (only some contactors picked up). What configuration do the motor windings form at that moment? • Then trace the circuit after the timer/CR changes state and a different set of contactors is energized. How are the motor leads reconnected for the running condition? • While the circuit is switching from the first condition to the second, is there any momentary break where the motor is completely disconnected from the line, or is there always some current path through resistors or contactors?

✅ Before You Answer

• Identify clearly which contactor(s) create the wye (star) junction of the three motor leads, and which ones connect the windings in delta across the line • Check whether the resistors R provide a path for current during the transition between contactor states (this is key to open vs closed transition) • Confirm from the drawing whether the motor starts in wye and then goes to delta, or starts in delta and then goes to wye before you choose between wye–delta vs delta–wye options