1. When choosing a contactor, the working environment should be considered, and the following factors should be considered.
①The AC contactor should be used to control the AC load, and the DC contactor should be used for the DC load
② The rated working current of the main contact should be greater than or equal to the current of the load circuit. It should also be noted that the rated working current of the main contact of the contactor is normal under the specified conditions (rated working voltage, use category, operating frequency, etc.) The working current value, when the actual use conditions are different, the current value will also change accordingly.
③ The rated working voltage of the main contact should be greater than or equal to the voltage of the load circuit.
④The rated voltage of the coil should be consistent with the control loop voltage
2. Specific steps for contactor selection
①Select the type of contactor, you need to select the type of contactor according to the type of load
②Select the rated parameters of the contactor
According to the controlled object and working parameters, such as voltage, current, power, frequency, etc., determine the rated parameters of the contactor.
(1) The coil voltage of the contactor should generally be lower, so that the insulation requirements of the contactor can be reduced and it is safer to use. When the control circuit is simple and the electrical appliances are relatively small, the voltage of 380V or 220V can be directly selected. If the circuit is complicated. When the number of electrical appliances exceeds 5, coils with 36V or 110V voltage can be selected to ensure safety. However, in order to facilitate and reduce equipment, it is often selected according to the actual grid voltage.
(2) The operating frequency of the motor is not high, such as compressors, water pumps, fans, air conditioners, etc., the rated current of the contactor is greater than the rated current of the load.
(3) For heavy duty motors, such as the main motor of machine tools, lifting equipment, etc., the rated current of the contactor is greater than the rated current of the motor.
(4) For special purpose motors. When it often runs in the state of starting and reversing, the contactor can be roughly selected according to the electrical life and starting current. CJ10Z, CJ12,
(5) When using a contactor to control the transformer, the magnitude of the inrush current should be considered. For example, for electric welding machines, contactors can generally be selected according to twice the rated current of the transformer, such as CJT1, CJ20, etc.
(6) The rated current of the contactor refers to the maximum allowable current of the contactor under long-term operation, the duration is ≤8H, and it is installed on an open control panel. If the cooling condition is poor, when the contactor is selected, the rated current of the contactor shall be The current is selected according to 1.1-1.2 times the rated current of the load.
(7) Select the number and type of contactors. The number and type of contacts should meet the requirements of the control circuit.
Post time: Mar-30-2023