1. The selection of the type of the DC contactor: The type of DC contactor should be based on the type of load current and the weight of the load to choose, that is, AC load or DC load, is light load, general load or heavy load.

2. DC contactor main contact's rated current: the rated current of the main contact of the DC contactor can be calculated according to the empirical formula, IN main contact ≥PN motor/(1~1.4) UN motor, if the DC contactor control motor starting, braking or reversal is frequent, in generally the rated current of the main contact of contactor will be reduced to use at lower level.

3. Operation Frequency Selection: Operating frequency refers to the number of opening and closing of contacts per hour. When the breaking current is large and the frequency is too high, it will cause the contact to overheat and even weld. If the operating frequency exceeds the specified value, should select the dc contactor with the larger rated current.

4. The selection of coil rated voltage: Coil rated voltage is not necessarily equal to the rated voltage of the main contact.