09 10 It is enough to switch the motor capacity less than 1KW frequently. It is estimated that the contact burn-out is due to excessive current and motor load, such as heavy workpiece and poor lubrication of the motion system; There are problems in the motor itself, such as unbalanced phase circuit, damaged bearing, faulty coupling and loose fixation. In addition, the quality of contactors is not genuine, so don't buy fakes.

Is there moisture regain in the control box and the humidity is too high?

Your engineer is talking nonsense. Actually, he is an engineer. Contactor controlled by PLC belongs to control circuit. What does it have to do with the capacity of contactor itself? The currents in the electromagnetic coils of 09 10 and 25 10 are almost the same. If the contact capacity of PLC can be controlled by 09 10, then 25 10 can certainly. The control circuit and the contactor on-off circuit are completely two lines. I don't know how the contact capacity of PLC affects the control ability of contactor.