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The principle of self-locking of AC contactors is easy to understand at a glance!

The principle of the AC contactor is that the power is pulled in, the main contact is closed and turned on, and the motor runs. This article introduces the self-locking circuit of the AC contactor and what is the self-locking of the contactor


1. Stop button

The wiring of the stop button should be connected to the normally closed contact. What is normally closed? You can understand it this way, if we don't press the stop button, the stop button is always on, press the stop button to disconnect, and release the stop button, it's still connected, so it's easy to understand!

2. Start button

The start button should be connected to the normally open contact. You can also understand the normally open as the stop button. The start button is always disconnected if we don’t press the start button. Press the start button and the line is connected. After releasing it, the line is disconnected and the start button And the stop button is also a momentary disconnection and connection, so understand!


3. Fuse

You can think of it as a fuse, it's easy to understand!

Principle introduction:
In the figure, we can see the circuit breaker, contactor, two buttons, a stop button, and a start button. Since it is a contactor self-locking circuit, we use the start button. Since it can be started, it must be stopped, so we use the stop button. The button is normally closed.

Wiring steps:

For circuit breaker 2p, the blue zero line enters the contact coil A1, the live line enters the red button = the stop button is normally closed, and the function stops the circuit. After the stop button is normally closed, two lines come out, and one enters the auxiliary contact of the contactor. Open NO (the contactor L1--L2---L3 contactor main contact is described here). Through the normally open NO of the auxiliary contact, it enters the coil A2, and the other one enters the normally open of the start button, and the function starts. The start button is normally open and the outgoing line enters the coil A2 of the contactor.

Run the demo:
Press the start button SB2, the contactor coil is energized, at the same time the main contact of the contactor is closed, and the auxiliary contact is closed. The main line power supply passes through the fuse to the contactor contact, to the thermal relay, to the circuit, and the auxiliary contact of the contactor is closed. At this time, the contactor has been energized due to the closed control circuit of the auxiliary contact.


Principle analysis:
Control circuit, because the control circuit is connected to the thermal relay normally closed contact, so the power supply passes through the thermal relay normally closed contactor KM auxiliary contact, when we press the start button, the contactor auxiliary contact closes the power supply through the contactor auxiliary contact to the contactor coil. So the contactor is always powered and the motor keeps running.

Post time: Jul-15-2022