13 March 2010 Author: Giorgos Lazaridis How Relays Work
Some types of relays
I've receive many emails concerning this subject. Relays are essential for automation systems and for controlling loads. Also, relays are the best way for galvanic insulation between high and low voltage portions of a circuit. There are hundreds of different relay types. Let's find out first how a relay operates.
Basic Relay Operation
Before extending to the various types of relays, i will first explain what and how the basic relay operates. Each relay has two mechanical parts inside. The first one is the contact(s) of the relay. The contacts operates similarly to the contacts of a simple switch or pushbutton. You should consider the contacts as a pair of metals like the following diagram:
The two terminals operates as a switch. When the contacts are 'in contact' then the current flows from Terminal 1 to Terminal 2. There are two types of contacts: the NO and the NC. NO stands for
Normal Open contact, while NC stands for Normal Closed contact. The Normal Open is a contact like the one showed in the previous illustration. When the contact is still, then no current flows through it (because it is an OPEN circuit). On the other hand, a Normal Closed contact allows the current to flow when the contact is still. Bellow i illustrate both of these contacts:
You may notice that the NC contact is turned upside-down compared to the NO contact. This is done in purpose. This way, both contacts (NO and NC) will change state if a force is applied to the left metal heading from UP to DOWN. The following animation shows how a NO contact operates by lighting a light bulb:
As for the NC contacts, it works exactly opposite as the NO contacts. Look the following animation:
A combination of contacts
A relay may have a combination of the above contacts. Look at the following illustration
In this case, there is a 3
rd terminal called "COMMON". The NO and NC contacts are referred to the COMMON terminal. Between the NC and the NO contact, there is no contact at any time! The following animation shows how this pair operates:
And WHO defines the NORMAL state?
OK, we have the NORMAL open and NORMAL closed contact. But which state is considered as NORMAL? Going one step closer to the relay operation, we find the spring. This spring defines the NORMAL position of the COMMON contact. If you see the above 3 animations, you will notice that one time an F force is applied to the COMMON terminal, and the other time there is no force applied. Well, this is actually wrong. There is indeed another force that pulls the contact towards UP and this force is applied ALL the time. This force comes from the spring. Look the following image:
Now you can see who is pulling the COMMON terminal UP all the time. So the spring defines what is the NORMAL state, and thus defines which contact is the NORMAL OPEN and which the NORMAL CLOSED. In other words, the NORMAL state is defined as the state that there is NO other force applied to the COMMON terminal except the one from the spring.
The last part - WHO moves the common contact of the relay?
This is the last part of the relay operation. The device that forces the terminal to move, is actually an electromagnet! A coil is placed right under the contact. When current is flown through this coil, a magnetism is created. This magnetism can overcome the force of the spring and can pull the contact towards it, thus it changes it's position! And due to the fact that the contact is usually a small piece of metal not capable to be pulled by the electromagnet, another piece of metal is attached to the common. This piece of metal is so called "Armature". Following is (at last) the complete illustration of the basic relay:
Now, imagine that someone wants to control a 220Volts 1 K-Watt load with a command that comes from a 5 Volts battery. A load-Relay should be used for this application. The Coil of the relay is driven with the 5 Volts. The contacts from this relay (NO) will be connected in series with the power supply of the load. Thus, the load will only operate when the relay is actuated. Our friend bellow will turn on an electric oven bare-handed!!!
Basic Relay Operation Looking inside the relay Relay Types Relay Symbols and Characteristics
At 4 January 2015, 9:18:31 user wrote: Giorgos Lazaridis [reply @ Giorgos Lazaridis] Well here is the deal. Long long time ago, the switches were like "knife" switches (check this page http://upload.wikimedia.org/wikipedia/commons/4/4b/Open_knife_switch.jpg)
See the similarity of a relay contact? The blade connects to the common, the other end that the blade goes in is the NO contact. So, it was common place to connect the live to the NO contact as safety measures, so that when the switch was off (open) the blade that was exposed would have no power.
BUT, this is not common use an more. Here is the other deal. If you want the relay to switch power between two loads, then the the live should go to common. Say for example that you want to power a traffic light for pedestrians, it can either be GREEN or RED, never both. So you connect the common to live power, the NC to RED and the NO to GREEN. Arm and disarm the relay to turn each of the lights ON or OFF...
So, it has to do with the operation that you want to perform. At 28 December 2014, 11:15:29 user wrote: Pammi [reply @ Pammi] Thanks a lot Giorgos..
I am new to working with Relays. Therefore, I have just one more question :-
In various other tutorials on Relays, I saw that LIVE wire was always connected to the 'Common' port of relay, and neutral to NO/NC (via Bulb/Microwave).
Is there any specific reason for that ?
I personally think that even if we connect the LIVE wire to NO/NC, and COM to neutral wire, it does not matter. It is one and the same thing.
But still wanted to have your view on that. Anything related to safety or something ? At 28 December 2014, 10:54:05 user wrote: Giorgos Lazaridis [reply @ Giorgos Lazaridis] @Pammi that would work the same, no problem. At 28 December 2014, 10:20:19 user wrote: Pammi [reply @ Pammi] This is so clear. Thanks !
I have a small Doubt: Why is the microwave (or any other AC component) is connected to power via NO/NC? Can we not the AC component to power via Common port of the relay ? Will there be any issue? At 7 November 2014, 17:33:08 user wrote: mahdi [reply @ mahdi] its the best explain about work relay.TANKS At 18 October 2014, 11:01:45 user wrote: sri [reply @ sri] will u please tell me brief about armature. At 18 October 2014, 10:59:11 user wrote: sri [reply @ sri] Thank you very much. It is good and the practical which u have shown is excellent and very understandable to me. At 7 October 2014, 13:57:26 user wrote: nivedha [reply @ nivedha] awesome
i understood clearly
thanks a lot At 18 September 2014, 13:50:07 user wrote: karim [reply @ karim] At 29 July 2014, 16:19:53 user wrote: ganesh [reply @ ganesh] At 16 July 2014, 15:51:06 user wrote: deb sankar mukhopadhyay [reply @ deb sankar mukhopadhyay] your explanation and animation is just awesome, keep the good work, God bless you. At 15 July 2014, 9:36:00 user wrote: Tony [reply @ Tony] good work..can yoy tell methe industrail realay connection and how its working At 23 May 2014, 19:27:21 user wrote: niki [reply @ niki] AWESOME tutorial. Basic concepts of relay is covered very well.
5 starts to the author. At 10 May 2014, 12:15:23 user wrote: meghan [reply @ meghan] Awesome to Undestanding.............. At 8 May 2014, 9:13:59 user wrote: Mohammed Wajeed [reply @ Mohammed Wajeed] hurrayyy !!!! finally found the way how relay actually works.. thanks for your good explanation and hard work :) At 7 May 2014, 10:14:54 user wrote: RAJESH G [reply @ RAJESH G] first of all .i thank uuuuuu..for this web page....it give more knowledge on basics ...thank u At 13 April 2014, 16:33:02 user wrote: jeff [reply @ jeff] i am a student and i found this very informative and understandable. thank you for this as i am sure i will reference it often. At 2 April 2014, 8:37:04 user wrote: Ram Krishna Sharma [reply @ Ram Krishna Sharma] Very good material conceptually as well as analytically. It will help students in projects as well as in ordinary applications of switching. At 13 March 2014, 18:31:44 user wrote: Michael G [reply @ Michael G] Thank you for this post. Of EVERYTHING on the internet about relays, this post finally made me understand.
Thank you. Thank you. Thank you. At 5 March 2014, 11:22:50 user wrote: sikandar [reply @ sikandar] At 3 March 2014, 3:46:31 user wrote: MOHD IMRAN QURESHI [reply @ MOHD IMRAN QURESHI] AWESOME TRICK OF EXPLAINING RELAY At 23 February 2014, 15:10:28 user wrote: godfrey [reply @ godfrey] Good and technical explanation
But where does the neautal go.thx At 18 February 2014, 15:39:54 user wrote: kunal [reply @ kunal] At 17 February 2014, 22:26:59 user wrote: SURAJ [reply @ SURAJ] Awesome to Undestanding.............. At 24 January 2014, 14:53:17 user wrote: ravi [reply @ ravi] nice and clear and got understood thanks a lot and keep giving information like this which helps us to improve our knowledge thanks............ At 3 January 2014, 9:54:45 user wrote: sahabh [reply @ sahabh] Jabardast...!!! THANX..!I Like it. At 15 December 2013, 6:05:06 user wrote: Ashesh Kharidia [reply @ Ashesh Kharidia] Understands Basics very easily. Very Nice At 26 November 2013, 4:17:32 user wrote: Gaurav [reply @ Gaurav] Nice and Clear. Animation is self explanatory. Thanks. At 24 November 2013, 18:27:24 user wrote: Rayar.B [reply @ Rayar.B] At 9 November 2013, 11:32:21 user wrote: naresh [reply @ naresh] nice teaching...... easy to understand At 26 October 2013, 17:32:41 user wrote: shradha g [reply @ shradha g] wooww.... nice..easy to understand . :) At 7 October 2013, 3:23:11 user wrote: aniket [reply @ aniket] very nicely written & it helps me to understand relay very nicely....
thx At 18 September 2013, 11:19:41 user wrote: Jacky Woo [reply @ Jacky Woo] Hi, I have a usb relay current - Up to 16Amp @24vdc or 250vac, I wanted make it work like a light switch to turn on a light on my front door! How would i wire it? Thank you in advance! At 16 September 2013, 11:21:58 user wrote: manikappa [reply @ manikappa] this nice experiment...... At 9 September 2013, 14:58:18 user wrote: chandan shee [reply @ chandan shee] At 29 August 2013, 6:17:34 user wrote: saravanan [reply @ saravanan] explaniation is very good.. keep going on... thanks a lot...from hereafter i can do the mini projects in my home... this website very useful for all... thanks alottt.... At 24 August 2013, 2:50:56 user wrote: FatnessFirst [reply @ FatnessFirst] I just want to say. THANK YOU. I've been researching about relays for 5 hours straight only to be left confused. You pretty much showed it in such an easy way and EVEN STATED that their are different kinds and purposes...no wonder i'm god damn confused the whole time At 20 August 2013, 11:29:43 user wrote: sanam pudasaini [reply @ sanam pudasaini] very good post... :) i expect more such post in coming days... At 3 August 2013, 6:59:04 user wrote: Jableen [reply @ Jableen] At 26 July 2013, 15:39:56 user wrote: birendra [reply @ birendra] very useful information ! thanks a lot, you really cleared my doubts regading relay opertaion. now i can do my home automation project without any fear of damaging my arduino., At 23 July 2013, 19:25:39 user wrote: Jayesh [reply @ Jayesh] Grate....
Well teaching trick.... At 20 July 2013, 5:32:09 user wrote: ananth [reply @ ananth] At 19 July 2013, 7:27:22 user wrote: TALHA [reply @ TALHA] At 11 July 2013, 13:06:14 user wrote: owen [reply @ owen] thanks i found it very virtal for i was confused on how i can make an automatic gate closer. If u do mind please asist me wth more illumination to this e-mail email@example.com thank u pipo At 23 June 2013, 16:02:02 user wrote: Lance [reply @ Lance] Nice post. Short and sweet. At 23 June 2013, 10:05:34 user wrote: Nelly [reply @ Nelly] Hi I have too signals to be brought back using relay? or relays? one is 24vdc for a plc signal and the other is volt free for a telemetry alarm how can this be done? At 20 June 2013, 4:43:10 user wrote: online education [reply @ online education] it is really very good post..
thanks At 20 June 2013, 4:11:08 user wrote: Gramzrah [reply @ Gramzrah] At 6 June 2013, 5:59:15 user wrote: zaeem [reply @ zaeem] At 21 May 2013, 15:22:39 user wrote: salik [reply @ salik] thanks brother it was very helpful for me. Nice animations. At 14 May 2013, 9:52:19 user wrote: Best [reply @ Best] This is very helpful! Thanks a lot for your efforts! At 10 May 2013, 11:46:44 user wrote: amol [reply @ amol] very simple to understand and impressive. At 20 April 2013, 2:26:14 user wrote: sudeep [reply @ sudeep] very nice explanation....good method to understand...use of animation is very helpful in understanding the concept...thanx alott:-):-) At 15 April 2013, 21:10:17 user wrote: Snehal [reply @ Snehal] Great explanation ! I finally have understood how a relay works ! I hope u keep the website updated with more explanations ! At 11 April 2013, 10:59:49 user wrote: Harry [reply @ Harry] thank you for giving this information,it is easy to learn and nice explanation.... At 10 April 2013, 17:49:12 user wrote: Abhijeet [reply @ Abhijeet] good one! very helpful, thanks... At 8 April 2013, 10:04:57 user wrote: kanyakumari [reply @ kanyakumari] very good explanation with showing pictures thanks a lot At 5 April 2013, 9:22:27 user wrote: Neelam [reply @ Neelam] thanks for giving clear idea about relay. At 29 March 2013, 20:19:17 user wrote: Giorgos Lazaridis [reply @ Giorgos Lazaridis] @ashmit maybe you want to control high load with small pushbutton or low voltage At 29 March 2013, 11:31:57 user wrote: ashmit [reply @ ashmit] why do we have to use the electromagnet to put the switch on and y cant we just make the contact with a simple switch. At 20 March 2013, 15:32:40 user wrote: manoj raut [reply @ manoj raut] That is very good method of understanding of relay opertion .
But ,can you explain how can we are use relay for fan control At 19 March 2013, 8:47:06 user wrote: saheer [reply @ saheer] Very helpful explanation thank u so much....... At 18 March 2013, 13:01:41 user wrote: Mnagesh [reply @ Mnagesh] Can you please explain me what is meant by the "Potential free relays".
As i want to integrate my device with the SCADA system they asked me to provide signal to SCADA device for 5 sec( means i want to complete there circuit using a potential relay) with the help of potential relays only.
Or can i use any kind of relay to complete there circuit. At 18 March 2013, 9:42:24 user wrote: Anusha [reply @ Anusha] At 11 March 2013, 17:47:43 user wrote: kiran kumar [reply @ kiran kumar] At 10 March 2013, 18:20:53 user wrote: kiran [reply @ kiran] really great!!!! this is so helpful.... At 7 March 2013, 19:56:21 user wrote: kimani morgan [reply @ kimani morgan] sent me more ok.!!!!!!!!!!!!!! At 7 March 2013, 2:19:38 user wrote: thilanka [reply @ thilanka] nice and simple explanation understood very well thank you sir. At 28 February 2013, 15:51:08 user wrote: Mystique [reply @ Mystique] thank u so much for the awesome explaination it really helped me alot At 23 February 2013, 5:18:56 user wrote: sram [reply @ sram] At 22 February 2013, 11:25:15 user wrote: Jayapriya [reply @ Jayapriya] At 20 February 2013, 14:37:17 user wrote: vijay patel [reply @ vijay patel] thanks for giving the article.
sir pls give me how many types of relay available in market with images pls reply me as fast as possible. At 22 January 2013, 11:18:00 user wrote: Amit Arora [reply @ Amit Arora] i dont think there is a better way to make some one understand the relay operation...thankyou very much it was very helpful At 16 January 2013, 12:03:12 user wrote: sourajit [reply @ sourajit] We can easily understand how Relay Work to study the chapter. At 29 December 2012, 6:50:04 user wrote: swamy [reply @ swamy] great explanation.which had given a good idea about it.i hope more component explanation from u...thanq At 28 December 2012, 18:17:07 user wrote: suresh kotgire [reply @ suresh kotgire] good one,really explained in a simple language with a detailled diagram. At 26 December 2012, 9:45:18 user wrote: Mangesh [reply @ Mangesh] gr8 explanation with the concept.....nicely understood....thanx At 23 December 2012, 15:26:49 user wrote: Aaron Chen [reply @ Aaron Chen] your explanation really help me understand what is relay about, I want to unerstand it from long time ago, but I just can't find other source that can help me understand easily like this! At 20 December 2012, 16:02:02 user wrote: virendra [reply @ virendra] very nice explanation of relay operation
Thanks Dear At 6 December 2012, 7:53:21 user wrote: Harish [reply @ Harish] excellent explanation. finally understood the principle behind relays, and now it appears so simple!! keep up the good work. At 3 December 2012, 7:10:28 user wrote: Etaa [reply @ Etaa] i thank you my fine sir. that was truly a good explanation. that clear everything up. your explanation and diagrams, true genius At 21 November 2012, 6:34:16 user wrote: karthik [reply @ karthik] At 20 November 2012, 2:25:41 user wrote: Prabhakar Kumar [reply @ Prabhakar Kumar] You are amazing .Very clear explanation with illustrative example.
Thank you and keep on it............ At 17 November 2012, 18:06:41 user wrote: saiden ayob [reply @ saiden ayob] very nice demo... Excellent.... At 2 November 2012, 8:52:31 user wrote: Sinith [reply @ Sinith] At 11 October 2012, 11:25:26 user wrote: Binomon Abraham [reply @ Binomon Abraham] Nice & simple explanation. Very good
Bino At 29 September 2012, 9:53:31 user wrote: Mohamad Hilman Bin Ismail [reply @ Mohamad Hilman Bin Ismail] thanx 4 your explanation,proud to be an engineer..
no doubt to take this course At 28 September 2012, 10:34:48 user wrote: aniket [reply @ aniket] At 28 September 2012, 1:25:37 user wrote: krishna [reply @ krishna] its simply so beautiful i never expected such a beautiful answer from internet At 25 September 2012, 16:00:50 user wrote: siri [reply @ siri] thank u so much... very useful to understand basic concepts of my small project At 25 September 2012, 11:02:50 user wrote: Bhagwati [reply @ Bhagwati] At 16 September 2012, 14:37:35 user wrote: Ansari yasar [reply @ Ansari yasar] At 9 September 2012, 17:56:34 user wrote: ajit [reply @ ajit] At 22 August 2012, 22:08:49 user wrote: Abe kaate [reply @ Abe kaate] good lesson with simple illustrations At 14 August 2012, 21:13:58 user wrote: hari rana [reply @ hari rana] really informative..very easy to understand.. thanks At 1 August 2012, 13:38:39 user wrote: sarang [reply @ sarang] At 29 July 2012, 12:21:42 user wrote: dayalraj [reply @ dayalraj] sir,
i also want to know about "limit switch" and its operation At 28 July 2012, 4:50:58 user wrote: jesu [reply @ jesu] super sir thank you a lot... need more from your side At 26 July 2012, 7:17:32 user wrote: T.dayalraj [reply @ T.dayalraj] i am a lecturer in a polytechnic. Now i can explain this relay topic in such a easy way to the students. i trust that every student can understand this topic about relay.
dayalraj At 18 July 2012, 8:16:22 user wrote: shubham [reply @ shubham] Grate..........best tutorial of relays At 3 July 2012, 8:13:46 user wrote: Giorgos Lazaridis [reply @ Giorgos Lazaridis] @Mohammad Nofal Yes you can do that,that is what they are designed for. The coil is completely isolated from the contacts At 3 July 2012, 7:43:48 user wrote: Mohammad Nofal [reply @ Mohammad Nofal] can we use two loads in the same relay output, one in NO & 2nd one in NC, does the relay coil or sping affected after several times of activation. At 25 June 2012, 12:25:55 user wrote: prasanna m r [reply @ prasanna m r] superb! solved all my confusions At 7 June 2012, 9:08:16 user wrote: muhammad imran mehdi [reply @ muhammad imran mehdi] well done very nice description At 28 May 2012, 14:21:06 user wrote: cabdikilaas [reply @ cabdikilaas] thank u very much so that these way is helpeful procces that can understand every one life over the world or use these technical At 25 May 2012, 5:42:25 user wrote: Dhruv solanki [reply @ Dhruv solanki] At 22 May 2012, 6:08:12 user wrote: mangesh [reply @ mangesh] At 26 April 2012, 14:22:58 user wrote: edresym [reply @ edresym] At 25 April 2012, 9:14:27 user wrote: rizwan iftikhar [reply @ rizwan iftikhar] so nice description sir ...... and please describe other electronic component like this one in detail and graphically....... At 17 April 2012, 10:04:53 user wrote: vinay [reply @ vinay] u explained it very easily At 15 April 2012, 16:53:55 user wrote: Sandeep [reply @ Sandeep] Very good post...... Thank u very much...... At 8 April 2012, 7:51:55 user wrote: Muhammad Nasir [reply @ Muhammad Nasir] very easy to understand and excellent step wise approach, thnx At 1 April 2012, 6:43:01 user wrote: hari [reply @ hari] thanx it was good.......and its language.is easy....... At 31 March 2012, 6:06:42 user wrote: A. Rafay Inayet [reply @ A. Rafay Inayet] The way of Explaining is excellent. It will be more helpful for beginners as well. At 27 February 2012, 11:21:53 user wrote: Giorgos Lazaridis [reply @ Giorgos Lazaridis] @shahzad you will need to use a transformer to convert 220 to 12. google for "ac/ac transformer" At 27 February 2012, 10:48:54 user wrote: shahzad [reply @ shahzad] how can i operate relay with 220v
and how can i convert 220v into 12v bc for relay operate At 8 February 2012, 12:04:43 user wrote: Lineo [reply @ Lineo] I would like to have theory of 110V DC monitoring relays.How does it work when it monitors that Voltage does not drop and if it does send an alarm? At 23 January 2012, 9:48:14 user wrote: adithyan [reply @ adithyan] thank u friend..,it helped me alot.... At 15 January 2012, 9:31:58 user wrote: jyothirmai [reply @ jyothirmai] thank you for giving this information,it is easy to learn and nice explanation.......... At 7 December 2011, 15:12:48 user wrote: krishna [reply @ krishna] nice explanation Thank u very much At 12 November 2011, 12:36:02 user wrote: Kammenos [reply @ Kammenos] @John Miller the latching relay At 12 November 2011, 5:51:46 user wrote: zahid [reply @ zahid] really nice animation for understanding the basic concept of relay. At 11 November 2011, 17:00:58 user wrote: John Miller [reply @ John Miller] What type relay DPDT will remain in either position without the coil energized. At 8 November 2011, 16:45:31 user wrote: Rakesh Bhati [reply @ Rakesh Bhati] Animated working is really very helpful to understand the basic concept of any mechanism....thanks for making this website...,,, At 26 October 2011, 11:51:48 user wrote: sujit [reply @ sujit] Really, Really......Thank u At 26 October 2011, 9:14:15 user wrote: shreyas [reply @ shreyas] really good work...helped me a lot. At 23 October 2011, 5:58:26 user wrote: Aniruddh [reply @ Aniruddh] Its a good presentation. I have understood a lots of things from this website...Keep it up.... At 12 October 2011, 10:09:48 user wrote: Ziyanal [reply @ Ziyanal] ya buddy, very nice....wish you would have been my teacher during my college days...thanks a lot At 11 October 2011, 14:46:42 user wrote: hsb [reply @ hsb] excellent explanation !!! keep more coming
thanx !! At 20 September 2011, 12:02:52 user wrote: pavithra.s [reply @ pavithra.s] really i like this of explanation.if we are reading in book.we can,t understand fully.sometimes it will be confusing.if we read the operations of instruments on animation,it will be usefull.so you have a good sense.please continue this. At 7 September 2011, 8:39:39 user wrote: sushil [reply @ sushil] Really nice explanation.One of the simplest explanations for understanding relays At 3 September 2011, 10:15:12 user wrote: Prashant [reply @ Prashant] Very easy explanation,Thanks At 26 August 2011, 13:55:02 user wrote: ram [reply @ ram] thank you for giving this information,it is easy to learn At 26 July 2011, 3:30:35 user wrote: krish [reply @ krish] Thanks a lot. What an clear/ excellent explanation... At 3 July 2011, 8:36:38 user wrote: ilavarasan [reply @ ilavarasan] this is the excellent explanation, thanks At 22 February 2011, 12:21:15 user wrote: Rasmi Ranjan Nayak [reply @ Rasmi Ranjan Nayak] Hello,
This is one of the best informative pictorial representation I have ever seen. The flow is very coherent.
Thanks Buddy.... Keep it Upppppp At 12 November 2010, 11:33:46 user wrote: Gangat Mohsin... [reply @ Gangat Mohsin...] Thank you for the serail flow for the process in detail...... At 28 June 2010, 19:01:31 user wrote: ravi [reply @ ravi] i like the way you discuss i really thankful that i got such a gud explanation. but i would like to request to discuss more on induction motor for industrial application.
H O T in eaven! h