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Components of AC contactor

Contactor is an electromagnetic automatic switch. It is an automatic electrical appliance that relies on electromagnetic force to close or separate contacts. It is used to connect or disconnect the motor or other electrical equipment circuits. It is suitable for connecting or disconnecting AC/DC main circuits or large capacity control circuits at a long distance.


Contactors are divided into AC contactors (voltage AC) and DC contactors (voltage DC), which are used for power, power distribution and electric field combination. In a broad sense, a contactor refers to an electrical appliance that uses the current flowing through the coil to generate a magnetic field to close the contact in order to control the load in industrial electricity.


The AC contactor is mainly composed of four parts:


(1) The electromagnetic system comprises an attraction coil, a moving iron core and a static iron core;


(2) The contact system, including three groups of main contacts and one to two groups of normally open and normally closed auxiliary contacts, is connected with the moving iron core and interlocked. The main contact is normally open, while the auxiliary contact often has a pair of normally open or normally closed contacts;


(3) Arc extinguishing device. Generally, AC contactors with large capacity are equipped with arc extinguishing device to quickly cut off the arc and avoid burning the main contact;


(4) Insulated enclosure and accessories, various springs, transmission mechanisms, short circuit rings, terminals, etc.


The working principle of the contactor is that when the contactor coil is energized, the coil current will generate a magnetic field, which will make the static iron core generate electromagnetic attraction to attract the moving iron core, and drive the AC contactor point action. The normally closed contact is open, and the normally open contact is closed. The two are linked. When the coil is powered off, the electromagnetic attraction disappears, and the armature is released under the action of the release spring to restore the contact. The normally open contact is disconnected, and the normally closed contact is closed. The symbol NO indicates normally open. Normally, the normally open contact is disconnected, that is, the coil is disconnected without power. NC means normally closed. Normally, normally closed contacts are closed, that is, the coils are closed without power.


There are coil identifications between A1 and A2 terminals, and their representative meanings are as follows:


M5 coil is AC 220v 50Hz, and M7 coil is AC 220v 50/60hz;


Q5 coil is AC 380v 50Hz, and Q7 coil is AC 380v 50/60hz.


AC contactor is generally used with auxiliary contact.


Selection of contactor


1. Rated voltage of main contact


The rated voltage of the main contact is greater than the rated voltage of the load.


2. Rated current of main contact


The rated current of the main contact is greater than the rated current of the load.


3. Rated voltage of coil


The rated voltage of the coil is selected according to the voltage of the control circuit.


Judgment method of coil


Turn the pointer multimeter to “R × 100 “gear, zero or set the digital multimeter to 2k gear.


2. Contact coil screws A1 and A2 through the probe. If it is zero, it means short circuit; If it is infinite, it indicates an open circuit.


Judgment method of contact


1. Turn the pointer multimeter to “R × 100 “gear, zero or set the digital multimeter to 2k gear.


2. Use the two probe points of the multimeter to contact the terminals of any two contacts. If the pointer does not move, it may be a normally open contact; No, it may be a normally closed contact.


3. If the pointer does not move, when the mechanical key is pressed, the pointer points to zero immediately, it is a normally open contact pair; After pressing the normally closed contact pair, the gauge needle returns to infinity from zero.

Post time: Dec-13-2022