What is Contactor? And where to use?

Contactor is a kind of automatic control device used to switch on or off the main AC and DC circuits and control circuits. Load current of ac contactor is very big, its internal coil to control its action or not, and the control coil is operated by relay connected to it. It tripped after a thunder is because the relay of AC Contactor  has over-current or ground fault protection function, when a thunder fall on a power line, it will control AC Contactor action, to cut off the load power to protect the equipment, and to avoid being damaged by the high voltage and big current or the ground safety hazard occurred.

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The contactor is an automatic control device. Contactor is mainly used for frequent switching on or off in the AC or DC circuit, has a large capacity of control, remote operation. When it is used in conjunction with vavious of  relays, can realize timing operation and interlock control, all kinds of quantitative control and under-voltage protection, it be widely used in automatic control circuit, main control object is a motor, can also be used to control other electric power load, such as electric heaters, lighting, electric welder, capacitor Banks, etc.

According to the type of control current, contactors can be divided into AC Contactor and DC Contactor. The commonly used AC contactors are mainly Electromagnetic Contactor and Vacuum Contactor.


1.   Electromagnetic AC Contactor type CJ.  Vacuum AC Contactor type CZ.

2.   The above models are standard models. In recent years, a new series B AC Contactor has been developed, and its model is BXX.


1.  Structure:

The contactor is mainly composed of electromagnetic system, contact system, arc extinguishing system and other parts.

(1).   Electromagnetic system:

Electromagnetic system including electromagnetic coil and core, is an important part of the contactor, rely on it to drive contact.

(2).   Contact system:

Contacts is the executive part of the contactor, including the main contact and auxiliary contact. The main contact is allowed to pass a large current, which can be used to connect and cut off the main circuit. Usually, the maximum current allowed to pass through the main contact (namely the rated current) is taken as one of the technical parameters of the contactor. Auxiliary contacts are allowed to carry only a small current and are generally connected to the control circuit when in use. The main contact of the AC Contactor is normally open, and the auxiliary contact is normally open or closed. The contactor with low rated current has four auxiliary contacts; With six auxiliary contacts for higher rated current.  (The so-called “normally open” and “normally closed” refer to the state of the contact before the electrified action of the electromagnetic system, that is, the normally open contact refers to the state when the coil is not electrified, its dynamic and static contact is in the open state, and the coil is closed after electrified, so the normally open contact is also called the dynamic closed contact.Normally closed contact refers to the coil is not energized, its dynamic and static contact is closed.When the coil is energized, it is disconnected, so the normally closed contact is also called the moving broken contact.)

(3).   Arc extinguishing system:

The arc extinguishing device is used to ensure that when the contact is disconnected from the circuit, the generated arc is reliably extinguished, reducing the arc pair contact damage. In order to quickly extinguish the open arc, the contactor is usually equipped with an arc extinguishing device, usually using a semi-closed longitudinal seam clay arc extinguishing cover , and a strong magnetic arc blowing circuit is equipped.

(4).  Other parts:

Including insulation shell, spring, short circuit ring, transmission mechanism.

2.  Working Principle:

When the solenoid coil of the contactor is not energized, the reaction force of the spring and the weight of the bit core keep the main contact disconnected. When the electromagnetic coil is connected to the control voltage (generally the rated voltage) through the control circuit, the electromagnetic force overcomes the reaction force of the spring and draws the armature to the static core, driving the main contact to close and close the circuit, and the auxiliary contact moves accordingly.


1.  Selection:

 (1).  The rated current of the main loop contact should be greater than or equal to the rated current of the controlled device, the contactor of the control motor should also be considered the starting current of the motor. In order to prevent the frequent operation of the contactor main contact ablation, The rated current of the contactor with frequent operation can be reduced.

(2).  The rated voltage of the solenoid coil of the contactor is 36V.110 v.220 v, 380 v, etc.The electromagnetic coil is allowed to be used in the range of 80%-100% of the rated voltage.

 2.  Maintenance

(1).   Items to be checked during operation: 1) whether the load current passing through is within the contactor rating;

(2).  The split-off signal of the contactor indicates whether it is consistent with the circuit state;

(3).  Whether the running sound is normal, and whether there is discharge sound due to poor contact;

(4).  Whether the electromagnetic coil has overheating phenomenon, and electromagnet short circuit ring whether there is un-normal;

(5).  Whether the arc extinguishing cover is loose or damaged.


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