Contactor Interlocking Circuit and Wiring Diagram

This article is about Contactor Interlocking. Here, you will know how to do the contactor interlocking step-by-step procedure. This article also includes with contactor interlocking circuit and wiring connection diagram. The contactor interlocking system has applications in motor starters (star-delta), power control circuits, power changeover circuits, etc.

What is Contactor Interlocking?

When an electrical circuit has two contactors and only one of them needs to be turned on at a time then the interlocking system is used. The interlocking system ensures that only one contactor can be on while another one will be in off condition even if we try to manually on it. 

An interlocking system is very useful for motor starters and power circuits. In a three-phase star delta motor starter, two contactors are used. One provides a star connection while another provides a delta connection. During the starting time the Star-connected contactor will be on and during the running condition delta connected contactor will be on. If both of them are turned on at the same time, there will be a short circuit. So the interlocking system in a star-delta starter prevents the short circuit.

The interlocking system in a changeover circuit helps to connect the load with one source of power supply and isolate it from another source of power supply.

Read Also: Contactor holding circuit with Push Button Switch

Contactor Interlocking Circuit Control Diagram

Here you can see the control diagram for contactor interlocking.

As per the above control diagram, you can see the coil of contactor 1 is connected through the NC points of contactor 2, and the coil of contactor 2 is connected through the NC points of contactor 1. 

So when contactor 1 is in ON condition, its NC contacts become open so contactor 2 can not be turned on even if we push the switch S2 to turn on contactor 2 manually.

When contactor 2 is in ON condition, its NC contacts become open so contactor 1 can not be turned on even if we push the switch S1 to turn on contactor 1 manually.

Read Also: Electrical Contactor Connection and Wiring Diagram

Contactor Interlocking Wiring Diagram

Here the step-by-step procedure is given below to make the wiring for interlocking of the contactor.

Step 1

Here you can see we have taken two contactors and the three-phase power connection given below figure.

Step 2

Now connect the A2 terminal of both contactors with neutral as shown in the below figure.

Step 3

Take a connection from the 'R' Phase and connect S1, S2, S3 as shown in the below figure.

Step 4

Connect the A1 terminal of contactor 2 to the S3 switch through NC contacts of contactor 1. See the below diagram for a better understanding.

Step 5

Now, connect the A1 terminal of contactor 1 to the S2 switch through NC contacts of contactor 2. See the below diagram for a better understanding.

Step 6

Now our interlocking circuit is complete. Now we are going to make the holding circuit. Connect the NO terminals of contactor 1 across the switch S2 and connect the NO terminals of contactor 2 across the switch S3. See the below diagram.

Step 7

Now our circuit is ready. Once cross-verify your circuit with the below wiring diagram.

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