According to the controlled object and work parameters, such as voltage, current, power, frequency and working system, the rated parameters of electrical ac contactor are determined.

1. contactor coil voltage should generally be lower, so that the insulation requirements of the contactor can be reduced, and it is safer to use. But in order to facilitate and reduce equipment, it is often selected according to the actual grid voltage.

2. the operation frequency of the motor is not high, such as compressors, pumps, fans, air conditioners, presses, etc., the rated current of contactor is greater than the rated current of load. Contactor type can choose CJ10, cj20 dc contactor and so on.

3. pairs of heavy duty type motors, such as machine tools, main motors, lifting equipment, winches, crushers, etc., the average operation frequency of more than 100 times /min, running in the starting, inching, positive and negative braking, reverse braking and other state. In order to ensure the electric life, the contactor can be used to reduce the volume. When choosing, the rated current of contactor is higher than rated current of motor.