It is no exaggeration to say: the contactor is by far the most frequently used electrical component in electrical operations.
The contactor is not only an effective part of the electric control cabinet, but also an effective part of the power distribution cabinet. More important in power control!
The use of contactors has almost laid the foundation of electrical engineering technology. The correct understanding and use of contactors is an essential skill for every electric operator.
Do you really know the four basic common sense about contactors?
The contactor is an automatic switching device used to connect or disconnect the AC and DC main circuit with load or the large-capacity control circuit.
The main control object is the electric motor. In addition, it is also used for other electrical loads, such as electric heaters, electric welding machines, lighting equipment, etc.
The contactor can not only switch on and off the circuit, but also has the function of low voltage release protection.
The contactor has a large control capacity and is suitable for frequent operation and remote control. It is one of the important components in the automatic control system.
Coils are usually identified by A1 and A2, which can be simply divided into AC contactors and DC contactors. We often use AC contactors, of which 220/380V is the most commonly used.
L1-L2-L3 is connected to the three-phase power supply line, and T1–T2-T3 is connected to the power supply line, which can be used to connect the load line.
The main contacts of AC contactors are normally open contacts, which are mainly connected to the main circuit to control the start and stop of motors and other equipment.
Auxiliary contacts of AC contactor
Contactor auxiliary contact (Upper Type)
Contactor auxiliary contact (Side Type)
Auxiliary contacts can be divided into normally open point NO and normally closed point NC.
For example: AC contactor normally open point NO and a red indicator light can be used as motor operation The indicator light, when the AC contactor is energized, the normally open point NO is closed, and the indicator light is turned on to transmit the operating signal of the motor or circuit.
For example: the motor forward and reverse control circuit is to use the interlock function of the contactor normally closed point NC.
For example: AC contactor normally closed point NC is connected to a green indicator light, which can be used as a stop indicator for the circuit or motor.
When the AC contactor is energized, the normally closed point NC is disconnected, the stop indicator light is off, and the corresponding running indicator light is on. , The circuit runs.
After electrification, the main contact is closed, the circuit is connected, the normally open point of the auxiliary contact is closed, and the normally closed point is disconnected to make the circuit produce a certain dynamic change and control the normal operation of the circuit.
The main circuit wiring is relatively simple, that is, three in and three out, top in and bottom out. All of these six or six lines must be connected to the main contact.
The main contact is supposed to be used for contact with electrical appliances or connected to the main circuit. It is necessary to pay attention to the exposed copper core not to be too long, otherwise it is prone to safety accidents.
It should not be too short, otherwise it is easy to contact badly. The screws should be screwed in with the right screwdriver, and the force should be balanced. After tightening the screw, pull it hard. If it cannot be pulled off, it is qualified.
The control loop generally uses auxiliary contacts on the contactor, combined with auxiliary buttons, relays or indicator lights, to achieve power supply control to the contactor’s coil through methods such as interlocking and self-protection.
The specific circuit and the specific control need are different, the following is an example of the asynchronous motor start control circuit.
The control point on the AC contactor has 220V, just connect two of 24V.
One end of 220V is live wire, and the other end is zero wire;
One end of 24V is positive and the other is negative.
Generally, small contactors have only one pair of normally open points, plus a set of coils, and three pairs of main contacts.
It is estimated that there is a pair of normally open and normally closed if it exceeds 32A. The normally open point is generally used for self-locking, and the normally closed point is generally used for interlocking.
When the electromagnetic coil receives the command signal and is energized, the iron core is magnetized into an electromagnet to generate electromagnetic attraction.
When the spring’s rebound force is overcome, the moving iron core is attracted to drive the contact action (the contact system is linked with the moving iron core) .
That is, the normally closed contacts are separated and the normally open contacts are closed; when the coil is de-energized, the electromagnet loses its magnetism, the electromagnetic attraction disappears, and the contacts are reset under the action of the spring.
The working voltage of the AC contactor coil should be 85%-105% of its rated voltage, so as to ensure that the contactor is reliably closed.
If the voltage is too high, the magnetic circuit of the AC contactor tends to saturate, and the coil current will increase significantly, and there is a danger of burning the coil.
On the contrary, if the voltage is too low, the electromagnetic attraction is insufficient, the moving iron core cannot be attracted, and the coil current reaches ten times the rated current, the coil may be overheated and burned.
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