2 Engineering2.11 Motor connectionDS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com 47Motors with considerably different motor outputs (e.g. 1.5 kW and 11 kW)should not be connected in parallel to the output of a soft starter. Reason:Starting problems may occur in the motor with the lower output since thiscannot provide the required torque.It is therefore advisable to only use motors with similar ratings (maximumdeviation: one rating size).Figure 30: Parallel operation of multiple motors on a soft starter (variant 2)2.11.8 Connecting motorsIf motors are connected in parallel and an additional motor is connected tothe soft starter’s output during ongoing operation, the soft starter will notcarry out a soft start for the new motor. However, the soft starter must beable to deliver the entire inrush current (approx. 6 to 8 times the rated motorcurrent) and the current for the remaining motors. Otherwise, an overloadwill occur and the soft starter may be destroyed in the worst case.￫ The total current consumption of all connected motors must notexceed the rated operational current I e of the soft starter.The overdimensioning of the soft starter is recommended if theindividual motors have high starting currents.￫ Each motor must be protected from overcurrent and thermaloverload (using overload relays and/or thermistor protection).￫ Motor-protective circuit-breakers (Q11, Q12) can also be usedhere instead of the overload relays (F11, F12).￫ The last connected motor must not be switched off in operationsince the resulting voltage peaks may cause damage to theelectronic components in the soft starter and thus to its failure.M1 M2Q21L1 L2 L3T1 T2 T3M3 ~ M3 ~Q11 Q12
