ATLAS ZR 630 tripped due to overload motor

Dear Sirs, Please tell me how to solve my Atlas ZR630 problem is that it often shutdown due to “motor overload” after 30, 1hr, 2hrs or even if 1 month. I have checked all electrical condition such as: cable connection, motor insulation, motor shaft rotation and all this conditions are ok. I am looking forward to your reply! Best Regards,