Knowing the power of the motor can calculate the current it operates, and when the power supply is 380V, the estimated current is 2 times the power (if a motor power is 7.5KW, voltage 380V, then its current should be 7.5 x 2 x 15A).

When the power supply is 220V, the estimated current is 4.5 times the power. Based on the above algorithm, we can roughly calculate the operating current of the motor, then we can follow the current to choose the size of the contactor rated load. The contactor rated load current is less than the motor operating current and is not available;

Contactors are used on different loads, and the choice of contactors is different, if you say typing in detail it takes half an hour. Here's a brief analysis:

Electric load - the rated current selection for the general contactor is 1.1-1.2 times the maximum current;

Motor - consider the operation of the motor;

When the motor is reversed frequently or when the start and stop are frequent, the contactor current is 3.5 times the power of the motor;

Contactors are rarely positively reversed, and when the start-stop is infrequent, the contactor current is 2.5 times the power of the motor.