What is a Contactor? | Working Principles

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⌚Timestamps:
00:00 - Intro
00:39 - What is a contactor?
00:55 - Why contactor is used?
02:44 - Contactor vs. relay
03:39 - How to wire a contactor
03:43 - 1) Coil terminals
04:53 - 2) Contacts terminals
05:55 - 3) Auxiliary contact terminals
06:10 - How does a feedback contact work?
07:08 - How to wire a contactor to the PLC and motor

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In this video, we will explain what a contactor is, how they work, how to wire a contactor, and the difference between a contactor and a relay.

A contactor is a device that is for making and breaking an electrical power circuit. For example, we usually use a contactor for turning on and off an electrical motor.

Why do we need to use a contactor? Can't we connect the motor directly to the PLC? Well, the short answer is no. Because you don't want to connect a high voltage electric motor to your shiny expensive PLC directly. This will damage the PLC cards if there are any electric surges on the motor's side.

We use a contactor to connect the PLC to the motor indirectly and safely. All contactors have a low voltage coil. We connect the PLC output to this coil. This coil usually works with a 24-volt DC signal.

Once the coil is energized, an electromagnetic field will be created. This electromagnetic field then causes the contacts to be closed and that's how the 3-phase power will reach the motor and can turn it on. So, there is no electrical connection between the coil and the contacts.

In the normal state and when the coil is not energized, the contacts are open and when a 24-volt DC signal is sent from the PLC, the coil will be energized, the contacts will close and the motor turns on.

A relay works the same way as a contactor. That means a relay also has a coil and some contact. When the coil is energized, the contacts will close.

But here is the difference... a relay is usually used for smaller devices with lower current and voltage rates. A contactor, however, is used for bigger devices with higher current and voltage rates.

Let’s talk about the wire terminals on the contactors.

1) On the front of the contactor, we see two wire terminals of A1 and A2. This is where we can connect a 24-volt DC power to the coil to energize it.

The coil may work with different voltages such as 12-volt DC, 24-volt DC, or maybe 220-volt DC.
Depending on the type of the contactor, the coil can also work with a 24, 120, or 220-volt AC power.

2) On the other side of the contactor, we have six other wire terminals. The wire terminals on the top are labeled from left to right with L1, L2, and L3. The wire terminals on the bottom are labeled from left to right with T1, T2, and T3.

The L1, L2, and L3 terminals are where the power wires connect to the contactor. The T1, T2, and T3 terminals are where the device wires connect to the contactor.

3) We have another set of wire terminals on the front end labeled as NO or normally open. This is a simple normally open contact referred to as an auxiliary contact or a feedback contact.

This contact is used to send a signal to the PLC input about the contactor's health. When the coil is energized and the three main contacts are closed, the feedback contact will be closed as well and send a signal to the PLC input.

You also need a start and stop switch to be connected to the PLC input.

- When you press the start switch, the coil will be energized, the contacts will be closed and the motor will be turned on.

- When you press the stop switch, the coil will be de-energized, the contact will open and the motor will turn off.

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#RealPars #Contactor #PLC

[anonymous]

It's been more helpful this channel than my career in more than one aspect.

[leandroalmeida]

I'm going through the greatest challenge of my life: becoming an automation engineer in a industrial plant. I've got a degree in electrical engineering, which was more related to power supply systems, but not so much to automation... however, I accept the challenge anyway! And I have to thank You for sharing this knowledge in a so wonderful way! It's been very helpful for beginners like me!

[kenmichaels]

Probably one of the most lucid presentations on contactors I've run across. Great job!

[QuestionableAdviser_]

When a YT video explains much more clearer than my Engineer Teacher.

[mahuk.]

So glad I found this channel when I was starting my career. Your videos are always so easy to understand with the good narrative and the images. Than you so much. One day I'll come back to buy your courses even if I don't need them at that point.

[bmtamer]

In the past year I have seen many Hvac videos. This is by far one of the best channels I subscribed to. I promise to share with some of my school mates. Thank you sir! Respect and keep the knowledge flowing on a high pressure gauge!

[od]

These videos are great, although you can be in maintenance field for many years it’s always some details and concepts you may miss but going back and studying and just doing a little research clears up a lot of the fog that can be in you’re head about certain things

[iliapopovich]

Very well explained in American-English, recently I did a L3 PLC programming in UK and it was horrible. Anyway, I took the certification...And by the way regarding the contactors and relays, you can always put three relays instead of a contactor for some small motors temporarily, just check the ampers. I have an Arduino controller with 230v 10A, very small relays working even on 3.3v DC, so with them, I can easily switch On/Off a 1000W, 450V motor.

[Sanjay.M.Pillay]

I am in industrial automation domain from last 2 years and have referred many videos. But the quality and vibrancy of Realpars videos us exceptional ❤

[samalfellah]

Amazingly simple and interactive way of explaining.

[davidalvarado]

This was so helpful and helped me embarrass my lead for trying to troubleshoot a broken contactor incorrectly when it was working just fine!!!
thanks a bunch RealPars

[eugenepohjola]

Howdy. Nice basic knowledge.
However. I would be reluctant to connect a contactor coil directly to a PLC output. I would use a relay in between.
Also a backfire or free-wheeling diode over the contactor coil is mandatory with DC. There is a lot of induction in the contactor coil when engaged. This energy will rapidly burn the relay or PLC card contacts if not managed. With AC the backfiring problem is not as big but some backfire managing is still necessary by a suitable RC filter over the coil. Typical values are R = 100 ohm and C = 100 nF 500 V in series.
Regards.

[PeterKiiru-xz]

Well thought out clear and concise presentation thanks very much

[ashutoshsawant]

I have been waiting for contactor vs relay video since long. Thank you for this.

[Xaerorazor]

If I remember correctly, contactors use a bar across two contacts per line where it can split the voltage to prevent arcing, whereas a relay uses only one point where it will experience the full voltage drop across the contacts, when opening the circuit, so a relay will take damage when opening a higher voltage/higher current source when the contactor is designed to split the voltage across the 2 contacts and reduce possible damage from arcing.

[dmj]

What an excellent explanation of how a contact operates!🤩

[ricardogarcia]

Great video. Remember one thing. You must connect a thermal relay in series between the outputs of the contactor and the inputs of the motor, plus the output that indicates a overload as a signal to PLC.

[I_name_All_my_guns]

I'm not an engineer but in hvac school. This video really helped. Thank you!

[АнтонКвасов-бл]

RealPars you best! Real learn videos! Thanks!

[daruscole]

I Praise God and thank those who have designed and worked on (and may continue to do so) such things as this to make things safer and to help prevent damage to other things. I imagine that some or all of the specifics to the design of such things may have required much work and testing. God Bless them.