Star - delta - cam switch

The YΔ circuit is used to start larger three-phase motors with squirrel-cage rotors with reduced power consumption. This prevents the tripping of overcurrent protection devices due to the otherwise high starting current during direct starting.In the starting process, the three-phase motor is first connected in a star connection for starting and then the motor is connected in a delta connection. The power consumption of the motor when starting in star connection is 1/3 of the power in delta connection. YΔ switching has largely become obsolete due to the use of frequency inverters. In contrast to YΔ switching, frequency inverters can be used to realise reduced current consumption while still achieving a high starting torque.

Reversing switches as cam switches

Three-phase reversing switches are used to reverse the direction of rotation of three-phase motors. When switching over, two phases of the three-phase system are reversed so that the motor starts in the opposite direction. Usually, all three phases are switched and the motor is completely disconnected from the mains in the "0" position. In the next step, the motor is switched on again with two reversed phases.

SEO=star-delta + reversing switch. Star - delta - cam switch