I am trying to protect two power sources from two generators from overcurrent, under/overvoltage, under/overfrequency,etc. There will be two generators running during the day and one running at night, I have double throw switches to switch the two breaker panels to run on one generator each or to share one generator. One generator's relay will run almost 24/7 and the other will cycle once per day.(Generators not ran in parallel.) I do not wish to use a shunt trip breaker connected to the protective relays for this purpose because I do not have an uninterruptable power supply. I was thinking of using a normally open contactor instead. I know a regular electromechanical relay will not last long in this application. What I am wondering is if it would be best to use a solid state relay or a mercury relay or something else for this application? The generators are 83 amp 120/208 volt 3 phase 24 KW.