2 Engineering2.11 Motor connectionDS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com 492.11.11 Bypass circuit2.11.12 Bypass circuit for emergency operationIn pump applications there is a frequent requirement for the bypasscontactor to provide facility for emergency operation. A service switch isused to select between soft starter operation and DOL starter operation viaa bypass contactor (Q22). This is used to fully isolate the soft starter. In thiscase, it is important that the output circuit is not opened during operation.An interlock ensures that a switchover is only possible after a stop.The electrical and/or mechanical interlocking of contactors Q22 and Q31ensures a safe operating state. CAUTIONThe output of a soft starter must not be connected to anycapacitive loads (capacitors)!This would damage the soft starter.￫ Devices of the DS7-34… series are already equipped withintegrated bypass contacts.An external bypass is therefore not required.￫ Unlike simple bypass operation (parallel contact with thethyristors in continuous operation), the bypass contactor mustbe designed here in accordance with utilization category AC-3since it must be able to start the motor directly. For a suitablecontactor, the contactor recommended in the Appendix(￫ page 223) can be used.
