These foot switches are designed for some critical applications such press brake machine control. These foot switches have at least one of the pedals with 3 positions, with a pressure point, to control dangerous movements.
For press brake control as an example:
press the pedal to lower down a press brake. It has 4 working contacts ( 2NC+2NO) to drive the movement and one safety switches (1 positive opening NC contact + 1NO) to stop the movement. Pressing the foot pedal, until the pressure point where resistance is noticeable. This allows the changeover of the 2 working contacts and press is moving downward. When press harder beyond the pressure point, the 2 working contacts return to their first position and the positive opening safety contact is activated as redundant safety circuit in order to initiate mmediately the dangerous movement. A restart of the machine is only possible after releasing the foot switch.