Self-Locking Circuit Work : Contactor Holding Circuit Explained

Added: 2026-05-18

[00:00:00]Understand the self-locking circuit in 1 minute. This is a self-resetting push button switch. When the button is pressed, the contact closed. When it is released, the contact opens again. Now connect the push button in series with the contacttor coil circuit. When the button is pressed, current flows through the coil. So the contacttor becomes energized. But once the button is released, the circuit opens again and the coil loses power immediately. Now imagine connecting a wire across both terminals of the push button. In this case, even if the button is released, current can still flow through the wire.

[00:00:34]So, the coil remains energized. But there is a problem. The push button now loses its control function completely.

[00:00:40]So, we need a connection that closes automatically when the coil is energized and opens automatically when the coil is deenergized. This operating principle is exactly the same as the normally open auxiliary contact of a contacttor. When the coil is energized, the auxiliary contact closes. When the coil is deenergized, the auxiliary contact opens again. Now connect this auxiliary contact in parallel with the push button. After pressing the start button, the auxiliary contact closes and bypasses the push button. So even after releasing the button, the coil continues receiving power through its own auxiliary contact. This is called a self-locking circuit.