All about Motors Direct-on-line start of three-phase motors
Typical circuit with bridging of overload relay during starting
The short-circuit capacity of the contacts in the circuit has to be considered when selecting F0. Two-way pushbutton
Control circuit device I: ON 0: OFF Method of operation: Actuation of pushbutton I energizes the coil of
contactor Q11. The contactor switches on the motor and maintains itself after the button is enables via its own auxiliary contact Q11/14-13 and
pushbutton 0 (three-wire control contact). Contactor Q11 is de-energized, in the normal course of events, by actuation of pushbutton
0. In the event of an overload, it is de-energized via the normally closed contact 95-96 on the overload relay F2. The coil current is
interrupted, and contactor Q11 switches the motor off. Application on drive motors with severe starting duty
Control circuit device I: ON 0: OFF
Q14: Bridging contactor
K1: Timing relay
Q11: Mains contactor
Method of operation
Actuation of pushbutton I energizes the bridging contactor Q14 which then maintains itself via Q14/13-14. At the
same time, voltage is applied to the timing relay K1. The mains contactor Q11 is closed by Q14/44-43 and maintains itself via Q11/14-13.
When the set time - which corresponds to the starting time of the motor - has elapsed, the bridging contactor Q14 is disconnected by K1/16-15.
K1 is likewise disconnected and, exactly as Q14, can only be energized again after the motor has been switched off by pressing pushbutton 0.
The normally closed contact Q11/22-21 prevents Q14 and K1 closing whilst the motor is running. In the event of an overload, normally closed
contact 95-96 on the overload relay F2 effects de-energization.
