My problem is minimized.But still sometimes communication stops,especially when one of contactors get on or a DC drive starts.

Hallo Mak,

I think you have a ground routing problem! Giving help is difficult without knowing any details. So, it might be very useful if you could give us much more details about your application. Please, a bit more of information... What DC drives are used, how powered, how controlled, what contactors, how many PCB, what kind of shielding, filtering, grounding...optocouplers? yes?, no?.....

Bye,
Kai