Today, let's learn how to correctly wire a contactor for self-locking. Before wiring the self-locking of the contactor, we need to understand the function and principle of the contactor, and what are normally open and normally closed main contacts? First, let's understand the role of the contactor.

The Role of the Contactor

A contactor is an electrical device that uses the magnetic field generated by the current flowing through its coil to close the contacts, thereby controlling the load. It is widely used in power generation, distribution, and consumption scenarios.Because a contactor can quickly cut off AC and DC main circuits and can frequently connect and disconnect large current control circuits (up to 800A), it is often used to control motors as well as factory equipment, electric heaters, working mother machines, and various power loads. A contactor can not only connect and disconnect circuits but also has low voltage release protection. With its large control capacity, it is suitable for frequent operation and long-distance control, making it one of the essential components in industrial control systems.

The Principle of the Contactor

A contactor is an electrical control device used to switch an electrical circuit on and off. The working principle of a contactor is based on the principle of electromagnetic attraction and release. When the coil of the contactor is energized, the coil current generates a magnetic field, which attracts the movable iron core to the stationary iron core, causing the AC contactor points to act - normally closed contacts open, and normally open contacts close; these actions are linked. When the coil is de-energized, the electromagnetic force disappears, and the contacts return to their original state under the action of the release spring, with normally open contacts opening and normally closed contacts closing.

Normally Open and Normally Closed

Normally open and normally closed represent the two basic working states. Normally open contacts are open under normal conditions and close only when a control signal arrives, making or breaking the circuit. Conversely, normally closed contacts are closed under normal conditions.

In addition to normally open and normally closed contacts, a contactor has main and auxiliary contacts. The main contacts can carry larger currents and are connected to the main power circuit, used to connect or disconnect the power supply to electrical equipment such as motors. Auxiliary contacts carry smaller currents and are connected to the control circuit, used to connect or disconnect the power supply to the contactor coil or relay coils. In complex control circuits, auxiliary contacts can act as intermediate relays for signal conversion or amplification.

The Principle of Contactor Self-Locking

The self-locking of a contactor is achieved by connecting the normally open contact to the normally closed contact. In this way, once a terminal of the contactor is energized, the contact closes, the current continues to flow through its own coil, maintaining the closed state of the contact. Even if the power supply is removed, since a circuit is formed between the normally open and normally closed contacts, the current can still flow, and the contact remains closed, realizing the self-locking function.

In contactors, a button is generally provided for manual activation. Pressing the button allows current to flow through the button's circuit to the contactor coil, creating a magnetic field that attracts the contacts to close. When the button is released, the circuit is interrupted, but the contact remains closed, thus achieving the self-locking function of the contactor.

Contactor Self-Locking Wiring

Now, let's take a detailed look at the circuit diagram and principle of contactor self-locking. Please see the diagram below:

In the above circuit diagram, the coil of the contactor is connected to the positive power supply through Button 1. Button 1 is connected to a momentary trigger (also known as a pulse trigger). When Button 1 is pressed, the trigger generates a short pulse signal, activating the contactor coil.

The normally closed and normally open contacts of the contactor are connected to the electrical load. When the coil of the contactor is activated, the normally closed contact opens, disconnecting the electrical load circuit; while the normally open contact closes, connecting the electrical load circuit.

Additionally, there is another Button 2 connected to the normally closed contact. Button 2 is used for jog control; pressing Button 2 closes the normally closed contact, allowing current to flow to the contactor coil, activating the contactor. Once Button 2 is released, the normally closed contact immediately opens, stopping the contactor from working.

The self-locking effect of the contactor is achieved through Button 1 and the trigger. After pressing Button 1, the trigger emits a pulse signal, activating the contactor coil and closing the normally closed contact. Even after Button 1 is released, the circuit remains closed because the current continues to flow through the coil. Thus, the contactor achieves self-locking functionality.

In summary, when Button 1 is pressed, the contactor is activated and locked, starting the electrical load; when Button 2 is pressed, the contactor operates in jog mode, energizing only while Button 2 is pressed. This way, through this circuit diagram, we achieve both self-locking and jog control functionality of the contactor.