Why do we have a shunt trip breaker or Isolation contactor in the enclosed Altistart ATS46 enclosed units?
It is for line isolation. Since the solid-state switches may be incapable of completely blocking motor power should a failure occur, 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.