What is a Contactor.pdf

What is a Contactor? Transcript: (00:02) in this video i will be talking about contactors i will explain what a contactor is and how they work i will also explain how to wire a contactor and the difference between a contactor and a relay [Music] if this is your first time here and you want to learn...

What is a Contactor? Transcript: (00:02) in this video i will be talking about contactors i will explain what a contactor is and how they work i will also explain how to wire a contactor and the difference between a contactor and a relay [Music] if this is your first time here and you want to learn more industrial automation topics and keep your knowledge up to date make sure to hit the subscribe button and the bell notification icon so you don't miss anything first let's talk about what a contactor is a contactor is a device that is for making and breaking an electrical power (00:48) circuit for example we usually use a contactor for turning on and off an electrical motor now you may ask why do we need to use a contactor can't we connect the motor directly to the plc well the short answer is no why 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 side so what we do instead we use a contactor to connect the plc to the motor indirectly and safely what do i mean by (01:27) indirectly you ask well 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 three contacts here to be closed and that's how the three-phase power will reach the motor and can turn it on looks like magic right so there is no electrical connection between the coil and the contacts the contacts will open and close via the electromagnetic field created by the (02:08) coil 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 with this setup there is no direct connection between the plc and the motor that's how you can turn on and off a big high voltage electric motor indirectly and safely and make sure your plc card won't be damaged if there are any electrical surges on the motor side so that's why we use a contactor (02:45) now that you know why we use a contactor you may want to know how a contactor is different from a relay you may say a relay also works in the same way can't we use a relay instead of a contactor to turn on the motor here the answer to this question is no 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 this is the same way a contactor works right but here is the difference a relay is usually used for smaller devices with lower current and voltage (03:23) rates a contactor however is used for bigger devices with higher current and voltage rates so relays are used to turn on and off small devices and contactors are used for turning on and off bigger devices very simple now let's talk a bit about the wire terminals on the contactors on the front of my contactor i see two wire terminals of a1 and a2 this is where i can connect a 24 volt dc power to the coil to energize it the a1 wire terminal is where the 24 volt dc positive signal wire gets connected and the a2 wire terminal is (04:03) where the 24 volt dc negative signal wire gets connected obviously the reason that i'm connecting a 24 volt dc power to these terminals is that the coil works with the 24 volt dc power for this contactor for some other contactors this coil may work with different voltages such as 12 volt dc or maybe 220 volt dc depending on the type of the contactor the coil can also work with ac voltage for example the contactors coil may work with a 24 120 or 220 volt ac power so before connecting the wires to the coil you first need to check the coil (04:46) voltage most of the contactors like the one i have here work with a 24 volt dc power on the other side of the contactor i 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 the l1 contact connects to the t1 contact the l2 contact connects to the (05:32) t2 contact and the l3 contact connects to the t3 contact all of my contactors contacts are normally open with the coil de-energized the device connected to the t1 t2 and t3 terminals does not have power when the coil is energized the device will now have power as you can see i have another set of wire terminals on the front end labeled as n o or normally open this is a simple normally open contact referred to as an auxiliary contact or feedback contact this contact is used to send a signal to the plc input about the contactors (06:16) health what do i mean by that the way that this contact works is that when the coil is energized and these three main contacts are closed this feedback contact will be closed as well and send a signal to the plc input however when the contactor is broken and energizing the coil will not result in these three main contacts being closed the feedback contact will not be closed either and no signal will be sent to the plc input this way there is a way for us to be notified if the contactor is broken we have discussed this more in our level 2 (06:54) plc programming course and there is a sample plc program that shows why we always need to use a feedback contact and how to use that contact in the plc program to get notified when the contactor is broken ok so to control a motor using a plc through a contactor you need to connect the plc output to the coil to be able to energize and de-energize it you connect a three-phase power supply to l1 l2 and l3 from one end and then from the other end you connect t1 t2 and t3 to the motor to be notified when the contactor is (07:33) broken you need to connect this auxiliary or feedback contact to the plc input you also need a start and stop switch to be connected to the plc input this way when you press the start switch the coil will be energized the contacts will be closed and the motor will be turned on when this happens the feedback contact will be closed as well and a signal will be sent to the plc input telling us that the contactor is working properly when you press the stop switch the coil will be de-energized the contact will open and the motor will turn (08:11) off in summary in this video you learned that we use a contactor to turn on and off heavy and high voltage electrical devices such as motors fans pumps etc you also learn that the reason that we use a contactor is to control these heavy high voltage electrical devices indirectly and safely via a plc and not to connect the plc directly to these output devices you also learn that the main difference between a contactor and a relay is that a contactor is used for turning on and off heavy high voltage devices but a (08:46) relay is usually used to turn on and off smaller low voltage devices that's it for this video i hope that you now clearly understand what a contactor is and how it works if so please don't forget to like this video this will help other automation engineers like you find this video more easily on youtube and it will also encourage us to create more easy to follow videos for you in the future want to learn plc programming in an easy to understand format and take your career to the next level head on over to (09:25) realpars.com [Music] [Music] Contactor, Electrical power circuit, Relay, Wire terminals, Auxiliary contact, Feedback contact