Problem is that both the STR and RU contactors are fed directly from the main line. When the contactor fused the only way to shut it down was shunting the main line.
I am unfamiliar with this unit, but are you saying the 3 ph goes thru STR and then RU? The reason why I ask this is the whole purpose of have 2 or 3 contactors is so if 1 does get stuck, is then the run timer trips, stops the control run up, which then would trip 'all' driving relays ie STR and UP. Unless STR is star and UP is delta. If that is the case, then this is a poor design of the 3 phase control. Also over temp thermistor should do the same thing. Every hydro that I have worked on has a MC contactor, then the star/delta changeover system which can protect for this problem.
Also having a soft starter also needs to have an input to say the run timer and over temp has tripped or else the same situation will happen. The best advantage of a S/S is for motor life without the in rush current breaking down motor insulation.
