Soft starters work by removing inrush currents from the motor during starting. It reduces the torque, without using star-delta starting, auto-transformers or resistor starting. Once the starting phase is complete (steady state), the soft starter is "bypassed" by a bypass contactor. A bypass is used to short-circuit the starter, bypassing the current flow through the contactor. 

They can control single to three phases, three-phase control generally giving better results.

The benefits of a soft starter 

Using a soft starter has many advantages. They allow smooth starting and a gradual increase in speed. In addition, the starter reduces the current draw at start-up and limits the current according to the load (torque control, current ramp, voltage ramp). Finally, the soft starter reduces the mechanical wear of the machines and eliminates the starting torque.

The different functionalities 

Soft starters have different functionalities, they protect against overloads of electric motors thanks to an integrated thermal relay. They have a fault output and they can perform a motor diagnosis. In addition, they can be controlled via a keypad or terminal block. Soft starters have a default memory and the curve can be set according to the application.