23 January 2021
Is a Line contactor required ahead of the soft start?
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.