Does the shorting contactor need to be oversized if it is to be used for full voltage bypass?
Yes. Shorting contactors are only rated for the AC1 rating. This means it is only rated to handle the continuous amps for the motor. It will be too small to handle the starting current. It is necessary to select full voltage bypass contactors based on the AC3 rating to handle the motor starting current. It is also recomended to use external overload protection because the soft starter will not be able to provide the motor thermal protection when removed from the circuit for full voltage bypass.