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Why do we have a shunt trip breaker or Isolation contactor in the enclosed Altistart Softstarts (ATS23, ATS46, ATS48, ATS22)?

Issue:
We install either a Shunt trip breaker or Isolation Contactor when building an enclosed or MCC installed softstart.  These options are also shown in our recommended wiring diagrams in the product documentation.

Product Line:
Altistart 22 (ATS22)
Altistart 48 (ATS48)
Altistart 46 (ATS46) - obsolete
Altistart 23 (ATS23) - obsolete

Environment:
All models, all versions.

Resolution:
This is for line isolation.
All softstarts use SCR's to switch the voltage during operation.
Since the solid-state switches (SCR's) may be incapable of completely blocking incoming power should a failure occur (they will almost always fail shorted), auxiliary isolation on the line-side of the controller is required.
The isolation device must be capable of operation via command from the Fault relay of the controller.
An isolation device consisting of either a circuit breaker incorporating a shunt trip coil or an electromagnetic contactor can be used to open the controller power circuit in the event of a controller fault.

This prevents voltage and current from passing through a damaged SCR and single phasing the motor.
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