These are the equipment which enable stepping or stepless manual speed control of the fans.
Stepless speed control switch is used for single-phase fan motors and provides maximum 5 A electric charge.
Stepping speed control switches are used for single-phase and three-phase motors. Voltage regulation is made by the transformer on speed control switch and speed is controlled. They provide maximum 10 A electric charge in single-phase fan motors and 18 A electric charge in three-phase fan motors.