Schematic diagram of weak current control strong current in power system, such as passenger control system?

I don't quite understand. For example, to control a 15KW motor, it is necessary to control an AC contactor with a button switch through a control circuit. This is weak current, and the contactor controls the motor current through the contacts, which is strong current. Look at the picture, it's intuitive. This is a star angle depressurization start-up diagram.