A Look at Thermal Overload Heaters in Motor Starters
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- Опубликовано: 2 июл 2024
- Today we take a look at thermal heaters, or overloads, in motor starters, including how they function and how to size them. Let's dive in and see what they're all about.
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Great explanation of a 3 phase motor starter. I thought you did a excellent job explaining the workings of the Motor starter.
Thank you I hope I was able to help you out a little.
Thank you sir! You helped me to figure out what size heaters I will need on a 25hp compressor. You explained everything very well and it was easy to follow your instructions. Thanks again!
Happy to help!
Just worked on this Motor starter yesterday and returned for more information on how they work. Fantastic job of explaining. Thanks!
I'm really happy this was able to help you out.
Great video! Answered all the questions I had from theory of operation to proper install👌🏽👍🏽
I'm really glad I was able to help out.
I don't know how i found your video but i am glad that i did. Thank you.
Thanks I hope it was a little helpful for you. I'll continue to do videos along these lines as the projects come through the shop.
Dude! I got a better understanding of how to locate my heater part number here than I did at the Square D website! Thanks for the concise and easy to understand instructions. I have a manual starter for a 5 hp motor but didn't understand how to figure what table to use on the Square D website. Thanks for this tool. I'm going to put it in my toolbox! Good stuff here.
Thanks,
I had a pretty rough go myself when I tried to size up my motor. I am really happy I was able to help someone out.
This is very thorough, detailed information on a highly technical subject. Thank you for sharing your insights.
Thank you. It's a fascinating device that can be great or a complete pain if not properly sized.
Excellent Video.
Thank you very much!
Good job.. Thanks for not rambling on about things that don’t apply
Thank you, very good explanation!
Very informative and helpful.... Thank you.
Good refresher from an industrial motor control class I took 2 years ago
Really great video. Very informative.
Very informative
Thank you!
Great video!
Great content! Thanks for sharing your electrical knowledge!
Glad to be able to help out.
Very nice. Especially the OL mechanisms inner workings. Thanks
Happy to be able to help
excellent, really descriptive
Thank you very much, this video took a fair amount of work to put together I am really happy it helped you out!
Thank you, sir!
We used these on our passenger boarding bridges at the airport. You made a great video to show my jr Tech's. They seem not to understand me with my accent 🤣
I am happy to be able to help out. It's one of those things that isn't hard but it definitely can be confusing until you see how the reference material is formatted.
Thanks
Very valueable video. Exactly what i was looking for. Only im using Allen Bradley's. These little gems can actually get rather pricy. Soft starter would be a better choice money wise, if you can trust the manufacturer. We were looking at starters for a 150 HP jaw crusher. 3 new Allen Bradleys would have cost over $30,000. What? Is there gold hidden inside or what? We opted for the chinese made soft start. $1400. It is interesting how you would need 3 AB's in a Wye configuration with a timer to do the same job. But the SS is also programmable. Thanks for sharing this. You have cleared up some gray area for me and i am in debt to you. Lol.
Allen Bradley is really nice gear but they are not cheap. They also can have some really long lead times these days. I think sometimes the prices on uncommonly sold items are higher and from the lead times I'm wondering if it's made to order. If that were the case it also explains some of the lead time issues.
@jb-ik8sj what brand was the soft starter?
@@mparim ATO. Comes from LA. most likely manufactured in China
@@mparim I was using generator voltage. Which concerned my some. Ive done industrial electrical maintenance for years. There was always 5 wires. So when 2 disappeard, i had to learn the concept of a balanced system. How I understand this is each wire is the return 20 times a second if your using 60Hz. Thats not common knowledge i guess as I found nothing on the web that explained that in layman's terms. Does that make sense to you? That is how it works right. I kinda came up with that on my own conclusion. NOBODY would help me grasp that. So then the control voltage on the soft start was just 2 of the legs. It did not matter which. Remember I am not an electrician. I was kinda grandfathered and guided by a few certified one's in the past. That was a valuable lesson I learned. Im going to the mine this week(6/24/24) to try to understand and install a solar system for the guard/crew house
Grasshopper....all in series !!!
You are correct. The overloads are mounted in mechanically operated contacts. Each of the three are connected in series. The neutral wire (generally) is connected through all three of them. If any one of the three open, the coil will lose power, and the starter will deenergize.
I am working on getting a junk started so I can tear apart the mechanism, and we can take a closer look at its operation.
Thank you for the comment.
Thank you❤
thanks!!
👍
Very well done, thank you! I'm new to this. Trying to learn more. I have a single phase 2HP dual voltage 110/220 motor. 20/10 Amps. The motor has a toggle that allows you to flip to 110 or 220.....just change the plug. I'm confused on how to wire the magnetic starter that came with the saw and I assume the heater would be rated for the 110- 20 AMP???
Thank you, If you are looking to operate it on 120V you will need to size according to the 120V specs for the motor.
This is awesome! Thank you. Question 🙋♂️ what happens when the heaters are installed upside down?
If you install them upside-down the little gear won't engage with the spring tensioner and the Normally Open contacts in the overload assembly will not reset (or close) when you press the reset lever. This style only installs one way. There is other styles however that I believe a 180 degree turn wouldn't matter. Do you have a specific Manufacturer and part number? I can try and look it up and answer a little more definitively for you.
So if it was 460 and the control voltage was 110, then that would have to come from a step down transformer. Correct? Again, thanks
Yes, normally there is a step down transformer for the 120V controls somewhere. Occasionally you will find the controls fed out if a 120V distribution panel. That is more common in the context of Motor Control Centers but 120v is 120v its up to whoever designed it to figure out where it is sourced from. The parts of industry I normally see are going the route of individual 480 to 120v control transformers so you can have a single point Lock Out Tag Out for both the controls and the power distribution. That being said I've definitely come across other ways of doing it.
The overload won't melt just expand and allow for the gear to rotate and open the neutral ...and you can reset it without changing anything....just fixing the problem.
The solder in the little pot temporarily turns into liquid due to the heat from the current passing through it. The gear being under spring tension rotates opening the neutral. Once the solder in the pot cools it resolidifies which allows you to reset the mechanism by reloading spring tension on the gear. You do not have to replace anything cause the solder resolidifies.
Granted over time they can get off and sometimes need replacing but that would be after a fair number of trips.
So the solder in the pot of the overload does indeed temporarily melt until it cools. The entire overload should not melt under normal operations, it can in some short circuit conditions happen and I am planning a future video touching on this. There's a few different way things fail but it will require something beyond over working a motor within normal operation.
I have a question on a similar style overload relay that has heaters but they are coil style Heaters. I had a overload relay that didn’t want to reset does this mean one of the heater was burned out ?
Without seeing it I would say it's very possible that the overload has failed that is always a possibility.
I believe I know the type you are talking about. It looks to me like the coil generates a magnetic field that tugs on a thin metal strip next to it which trips it. We had some here that had those strips broken on them. I'd look for that.
Thats very interesting. I've seen this style but never had to trouble shoot one. Next time I see one I'll take a closer look. Thank you very much for the input!
👍👍👍👍👍👍👍👍👍👍👍👍
Great vid., got a question. I have a 1950's era wood planer It's got a size 1 440v 60CY Allen Bradley mag. starter. My 3 phase 240v won't close it. Can change to a 240v coil and solve my issue? TY
Are there any markings on the coil of the contactor? Normally the coils are a lower voltage of some kind used to switch the higher voltage. Coils are always two wire hook up, they are normally much thinner wires. The contactor should say what voltage the coil is Allen Bradley is pretty good about that.
@@TalkingHandsTools The coil 40v 60C below that 464-3 contactor 440v 60 CY
Wow 40v is an unusual one. You will need to know a few things, I'll try my best to outline them below.
What voltage are you looking to run the planer on?
What voltages can the planers motor operate on?(if not compatible with desired voltage motor may need either change or transformer may be required)
How many amps is the motor at the desired voltage? (The current will say what NEMA size you will be needing)
What type of control voltage will you be using? (You may need or have a control transformer or a separate 120v feed for controls)
Once you have identified these things you should be able to source a new contactor/starter. From here you can size your overloads as well as your fuses if applicable.
Let me know how it turns out or if you have any other questions. Sounds like a fun project.
@@TalkingHandsTools Power source 240v 3 phase ... 2 motors, one 7.5 220/440
, one 1hp 220/440 ... amps 21 and 3 Iam going into the original machine mounted disconnect which feeds starter/power switch/motors. Best case for me would be able to replace coil w/220 60 cy..
Are there two starters that you need coils for or is one currently operable? I'm not sure how lucky you will be finding coils for something from that Era. Do you know if the contactors have been upgraded since the Era of the machine or if all is still stock?
Is the neutral on a normally closed ?
The overloads are a Normally Open contact held closed mechanically by the overloads. When the solder in the overloads heats up beyond the specified current of the motor the solder melts and when it melts it looses it mechanical resistance which allows the spring tension from the Normally Open contact the Neutral goes through to open up and turn power off to the Neutral going to the coil on the contactor.
In this case all three of the Normally open contacts (one for each phase) are wired in series that way if any one phase overloads it will shut the motor down by killing the Neutral going to the coil. Those three contacts are Normally not serviceable and are integral in the overload housing you cannot change the way they are connected you just have two contacts to hook to.
Hopefully I was able to explain that well enough. It's not too complex but not being able to physically see what's going definitely can lead to questions.
@@TalkingHandsTools I understood that part perfectly thank you. I was confuse on the installation and location of the neutral on the overload sides. Cause I sometimes see A1 A2 and I get confuse which the Coil really is
@@TalkingHandsTools I understood that part perfectly thank you. I was confuse on the installation and location of the neutral on the overload sides. Cause I sometimes see A1 A2 and I get confuse which the Coil really is
It's an easy thing to mix up. There should be a jumper wire from normally A2 to the overloads so the neutral can connect through the overloads. Great question. If you learn on normal relays, I can absolutely see the overloads confusing you when you connect them up.
So you need 3 even if you’re gonna just use 2 for a single phase motor?
We still will need all three for our project we will ultimately be running a three phase motor on single phase. If you were running a single phase motor you are correct you would only need to utilize two of the poles.
I have people in my industry for years telling me the "heaters" are going bad. However, nobody has ever shown me a reliable method to test them. I HAVE seen this be the case, but only to the extent that changing them fixed the issue. Does anyone know of a method to verify the heater has gone bad? This is generally in an environment that doesn't allow for controlling the load on the heater, so any ideas would be awesome.
We use the Square D heaters, just like the one in your video.
Short of load testing the only thing I can think of off the top of my head might be a heat gun and a thermal imager. The problem would be figuring out the temp the heaters solder should melt. If you knew that it might be worth a go. I might experiment with this if I can get a few different size heaters. The problem I expect will be translating a current rating to a temp rating. Theoretically though I would think you could mechanically test them with external heat as well. At least enough to know if it's way out of spec. That's an interesting one to ponder.
@@TalkingHandsTools thanks for the response. I can't think of a way to test them, and I hate simply replacing parts guessing. It just so happens we don't have ready access for monitoring them. They are sealed up tight in an explosion proof panel, so I'm sure we waste a lot by not having a method to test them. The heat gun and thermal imager should work, as long as testing a few new heaters will give you a fairly accurate average. About the best idea I've heard, because I have never heard anyone give a way to test them.
Correct me if I’m wrong but a continuity test works
If the thermal unit is still good, you will have continuity.
A blown thermal (heater) will have no continuity.
I'm not sure continuity would confirm they are in spec. If they read open, it would be a catastrophic failure. I'm not sure the heaters themselves would actually open under an overload condition. The solder alloy in them would definitely turn fluid, which would allow the spring-loaded mechanical contact they keep closed to open and shut the motor off through operating the coil.
But that being said, the overload itself has to continue to conduct electricity itself up to the point the solder alloy melts. I suspect if the spring-loaded overload mechanism fails and does not open, the solder alloy might experience thermal runaway and fail catastrophically.
What is difficult is overtime and duty cycles (being tripped repeatedly) the solder alloy doesn't stay consistent in its tripping point. I do believe they generally trip sooner, but that comment only comes from having to replace ones that trip sooner than they normally should. If some trip later, we'll those would eventually result in a motor failure. That is the reason some maintenance programs change the overloads if a motor fails no questions asked. It's also at the route of the speculation on how to test them.
I hope I explained that okay. There's a ton of nuance to overloads and it's a little hard to articulate everything that's going on. If you have any ideas, I'm definitely game to talk them over.
Are these heater units reusable or do they require replacement after every trip?
The heaters are a solder alloy that is calculated to turn fluid at a specific temperature. The temperature is achieved by current flowing through the circuit. As the current increases it will increase the heat, thus the nickname "heater". The solder is contained in a specially designed unit that sits under spring tension. As the solder heats up and becomes fluid it can no longer hold the spring tension as a result the springs overcome the mechanism and open the contacts which turns off the power in the circuit. That being said after the solder cools down it becomes solid again and allows you to reset the spring mechanism that allows power to once again flow through the circuit.
So the quick and easy answer yes they are indeed reusable.
You highlighted 3 TU ( assuming 3-phase then) and motor plate showed 1.6 amps for 460. Why then use the 3.2 amp on the heater table? Seems oversized then.
Thanks for the comment. We will be using the 240v hookup in this case so we will need the 3.2 amp heater. You are correct if we were hooking this motor up for 460v we would indeed be oversized.
Depending on what motor starter you have depends on the motor and the he voltage. A lot of motor starters have two or three hot legs and no neutral. Most starters don’t have a neutral as you are showing. I think you know enough to be dangerous !
Motor starters can have one two or three phase legs, all starters with electric coils require an additional power source to operate the coil on the starter. In this case it is 120V AC it could be any number of voltages but 120V AC and 24 V DC are more likely there definitely are 240V AC and even 480V AC but the coils voltage specifications are something entirely different. That being said this coil requires 120V AC which in North America does indeed require use of a neutral. So while the neutral is not found in the motor part of the circuit the neutral is most definitely required to make the starter go Ca-Chunk and close. In this case the neutral is also routed through the overload contacts which, in the even of an overload condition opens the neutral thus de-enrgizing the coil which in turn turns off the current to the motor.
To try and distill it down as far as possible the motor starter is an electrically operated switch exactly like a relay or a contactor the only real difference is the addition of the overloads. A much smaller voltage and current can be used to operate a much higher voltage and current that is why they are so advantageous to use.
Hopefully I was able to make that a little more understandable I recognize if it's not your thing it can be a little confusing to understand all that's going on with a starter.
3 phas? No matrix # + descript - in calculus! You lied - on public property!
You've got me confused. Could you elaborate a little more with some details? This is a three phase motor starter. Are you saying it isn't?
You are explaining a 3 phase starter , with 3 phases you don’t have a neutral! Go back to school .
I am indeed explaining a three phase starter. There are only three phases on the contactor itself. The neutral in this case with a 120V coil is on the coil only and while it's on this piece of equipment it is terminated only on the coils contacts not the contactor.
Three phase can indeed have a neutral. If your in North America and go to any commercial place you will likely find either 480V Y which will have a 277V Phase to neutral. Or you may see a 208V Y which will have a 120V phase to neutral. If it's an older installation you may see a 240V Delta which has 120V between two of the phases and around 208V to the third this is known as a high leg or wild leg and can be quite dangerous if you do not understand what is going on. I've in recent years even been installing 400V Y systems which generate a 240V neutral. These are especially beneficial to labs that utilize more European equipment. A 240V single phase system could also be used but that isn't advisable due to creating a phase in balance on the installation which isn't overly desirable. With the 400V system you can balance your phase loading and still power your gear.
All that being said to be honest a significant amount of the 3 phase used in North America you will likely find a neutral with of some kind. There most definitely 3 phase installations with no neutrals but to say that no 3 phase installation has a neutral would be a vastly inaccurate statement to make. It would also be a very dangerous statement that could lead to many people being seriously injured.
Hopefully I was able to explain a little more about neutrals and 3 phase I know it can be very confusing. In the context of this motor starter the starter only switches the 3 phases and it uses 120V single phase with a phase and a neutral to operate the coil. The neutral is indeed switched within the overload part of the starter this makes the coil de-energize thus turning off the 3 phase in the event of a motor overload condition.
He is explaining the control circuit not the power circuit 🤦♂️
Thank you for the comment, I tried to explain as best I could. I'm glad you understood the neutral in this case is used in the control part of the contactor and is routed through the overloads. Thank you again for the comment.
you embarrassed yourself here dude.@@TalkingHandsTools
What do you think I have mixed up? The coil of a contactor with 120v control like the one in the video requires a neutral, and the neutral is switched by the overload assembly. If any of the three overloads trip, the neutral is opened, and the coil of the starter denergizes.
Do you know of a starter that operates differently? I'd be game to learn about and do a video on it.
Great explanation. Thank you.
Thanks for your feedback. Glad you enjoyed it.