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What is contactor?

Time:2022-12-06   Author:As Beam   Browse:

Today we're going to talk about contactors. The main contents are:

  • How contactors work

  • The difference between contactor and relay

  • The wiring method of the contactor




1. What is a contactor

First of all, let's take a look at what is a contactor?

It is an electrical component used to turn on and off the power supply.

For example, we often use contactors to start and stop a motor.



2. Why use a contactor?

You may ask, why use a contactor? Is it not possible to directly connect the motor to the PLC for control?

the answer is negative.

Why is this? Because you cannot directly connect a high-voltage motor to an expensive PLC. If you do that, once there is a surge on the motor side, the PLC module will be directly broken.

The correct way is to add a contactor between the PLC and the motor for indirect control, which can also protect the PLC.

What does "indirectly" mean here?

In fact, there will be a low-voltage coil in all contactors. We connect the output of the PLC to this low-voltage coil, and the operating voltage of this low-voltage coil is usually DC 24 volts.

As long as the low-voltage coil is energized, an electromagnetic field will be generated, and this electromagnetic field will attract the three contacts here, thereby conducting the power circuit and making the motor start.

It should be noted that there is no direct physical connection between the coil and the contacts here. The on-off of the contact is completely controlled by the electromagnetic field generated by the coil. When the coil is not energized, the contact is disconnected; when the PLC sends a 24 volt DC signal, the coil is energized, the contact is closed, and the motor starts.

By configuring the contactor, the PLC and the motor do not need to be directly connected, so there is no need to worry about the PLC module being damaged due to the surge of the motor.

Eaton Contactor.png



3. What is the difference between a contactor and a relay?

We have already known the benefits of using a contactor, and then let's talk about the difference between a contactor and a relay.

You might say, don't relays and contactors work the same way? So can we use a relay instead of a contactor to start the motor?

The answer is still no, let us analyze.

In fact, the working principle of the relay is the same as that of the contactor. That is, a relay also has a coil and some contacts. When the coil is energized, the contacts close.


But there is a difference here because relays are usually used for smaller current and voltage devices. The contactor is used in higher voltage equipment.

In summary, relays are mainly used to switch small devices, while contactors are used to switch large devices.

In fact, from the appearance point of view, the contactor is large and the relay is small, and the difference is obvious.

Moeller Contactor.png



4. Wiring method of contactor

Next, let's look at the terminals on the contactor.

4.1. Coil terminal

On the front of the contactor, you can see two terminals, A1 and A2.

These two terminals are used to connect DC 24V power supply;

The A1 terminal is connected to the positive pole of DC 24V, and the A2 terminal is connected to the negative pole of DC 24V.

The reason why 24V DC is connected to these two terminals is because these two terminals are connected to the coil of the contactor.

Eaton Contactor 1.png


Of course, there are contactors of other specifications, such as DC 12 volts or DC 220 volts. Not only that, but there are also some specifications of contactors whose coils can use 24 volts, 120 volts or 220 volts of AC power.

Because there are many specifications of the contactor, we must check the rated voltage of the coil before wiring the coil of the contactor.

Like the contactor in the picture, it uses DC 24V power supply.

4.2. Contact terminal

On the other side of the contactor, there are another 6 terminal blocks.

The top terminals are labeled L1, L2, and L3 from left to right.

The bottom terminals are labeled t1, t2, and t3 from left to right.

New industry Technology regarding to Bussmann fuse, ABB breakers, Amphenol connectors, HPS transformers, etc. 

TAG:   contactor Eaton Moeller Siemens