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There are other limits of installing a contactor on the frequency inverter input side, including possible damage to the DC bus capacitor pre-charge circuit. The pre-charge circuit will be designed for a certain amount of operations/hour. Is it acceptable contactor(s) to use late-make/early-break auxiliary contact on the output, wired back to the inverter?The early-break contact should break around 500ms before the main legs to be effective. Typically-available 10ms early-break aux-contact isolators are ineffective as the residual motor field will not have decayed, resulting in an inductive kick 10ms later when the 3 main legs open. Pffff! goes the frequency inverter output! It is unclear in this situation what a suitable isolator could be. The only practical solution is a lockable isolator, the expectation being that the person with the key understands the need for care.
If one is expecting a lot of switching on the input, then this could be a problem. If an early-break contact on the contactor is used to panic-stop the inverter first, then that may be okay. It depends on the timing and also how the inverter responds to this sort of treatment. Some are more tolerant than others. Consult the manufacturers of the inverter.
In the case of an emergency, nothing can stop the motor faster than the inverter itself (most inverters having an E-Stop input anyway). How the frequency inverter handles the emergency condition is usually a programmable function: ramp down at max or coast. This assumes, of course, that the inverter is undamaged, one would be wise to tie in a line or load contactor to the NO (normally open) output of the inverter-status relay. If it's an emergency, break it on the load side (inverter output). Nobody at the inquiry is going to sympathize with your concerns to pamper the thyristors when weighed against the potential risk to human life.