Is a Line Contactor ahead of the soft start required as referred to in the ATS22 users manual?


07 January 2022

Is a Line contactor required ahead of the soft start?

Product Line:
Altistart 22, ATS22

All models and serial numbers


The purpose of the line contactor is to provide a means of removing AC line voltage from the softstart.  Due to leakage currents through the solid state switches, hazardous voltages can be present on the load side of the softstarter when power is applied to the line side of the softstarter. 
Also, the line contactor can be controlled to open if the ATS22 faults.  Some faults are the result of SCRs shorting.  If multiple SCRs fail in a shorted condition, full voltage power passes through and will either single phase or continue to run the motor.  The KM1 would interrupt  the power circuit.

A line or isolation contactor such as KM1 shown in wiring diagrams, located in the Annex of the ATS22 Users Manual (BBV51330) is strongly suggested but not required.