Typical circuit diagram of Star Delta starter
S0 = ‘OFF’ Push button S1 = ‘ON’ Push button K1 = Line contactor K2 = Star contactor K3 = Delta contactor K4 = Star delta timer (7PU60 20) F2 = Overload relay F1 = Backup fuse F3 = Control circuit fuse This is a starting method that reduces the starting current and starting torque. The device normally consists of three contactors, an overload relay and a timer for setting the time in the star-position (starting position). The motor must be delta connected during a normal run, in order to be able to use this starting method. The received starting current is about 30 % of the starting current during direct on line start and the starting torque is reduced to about 25 % of the torque available at a D.O.L start. This starting method only works when the application is light loaded during the start. If the motor is too heavily loaded, there will not be enough torque to accelerate the motor up to speed before switching over to the delta position. When starting up pumps and fans for example, th...