Hello! One thing I didn't touch on here was the power draw of the contactor itself. For the contactors I'm showing here it's quite small (just a few watts) but there are some applications where a latching contactor may be desired. These have two magnets - one to close the contactor, and another to release it. These can save some energy, but come with the risk that a control system failure may leave the contactor engaged. Depending on the application, that could be _very bad_ so they're far less common.

Finally, a video on this channel is actually about technology making (or breaking) connections.

"I said we wouldn’t get lost in HVAC trivia." The whole video is trivia and we're here for it. Embrace it. Distribute it.

I just want to say as an hvac technician your channel has been invaluable for showing less tech minded coworkers breakdowns for things we touch everyday. Your refrigeration episodes genuinely get pulled up very often

5:20 fun fact, this is also a major reason why restoring power after a blackout is trickier than you'd think. If you restore too much coverage at once, everything that's plugged in will restart and momentarily draw startup current at the same time, which runs the serious risk of blacking the grid right back out again.

As an HVAC tech I would happily show this video in a classroom setting to people who are learning about HVAC. Everything you said was correct!

As an electrician that works mostly in commercial and industrial jobsites I appreciate the way you can explain something so simply anyone could understand like an apprentice. I will use this as a reference when explaining these to those apprentices who just don't seem to get what I'm saying

I worked for a low voltage company at one point and had access to the elevator room in an old skyscraper. It was literally an entire room filled with contactors. Probably hundreds of contactors big and small just click clacking away as people would call and use the elevator. It was a very impressive show and mesmerizing to watch.

One common criticism in movies is that stadium lights don't actually make that "chunk" sound when they come on. But a warehouse I used to manage used contractors to control the lights, and they made the most satisfying "chunk" sound when activated.

You have to respect a guy who has a favourite type of contactor.

One thing you mentioned when contrasting the contactors with relays is that they don't have normally closed contacts. In the field of industrial automation, it's actually very common for them to have additional normally closed contacts, either in the form of a 4th pole that's normally closed, or an auxiliary, low-current contact block that gets attached to the contactor. The purpose of these is to allow detection of welded contacts, as if one of the contacts welds closed, the normally closed contact won't close when the coil is de-energized. I have some old leftover ones lying around that I could send for a connextras video if you're interested!

As an electrician-in-training, I feel noticed to have people finally understand the joys and pains of working with contactors

The spiciest contactors are the ones that have been in service long enough to stick closed, or at least stick closed enough to arc. Those are fun!

I like everything out of this channel because it explains the kind of things that old corporate videos explain without the associated vested interest.

I spent a summer as a brakeman on a short-line raiiroad. I had a big "aha" moment here when Alec mentioned the "gnarly" contactors on locomotives. Suddenly, the big loud click that happened when the locomotive was put into dynamic braking made all kinda sense. Thanks, Alec!

My sister and I drove from SF to Vegas a few weeks ago. It wasn't until the fifth or sixth charge that I realized how much juice was being moved. She was chatting with another Mach-E owner about how some relays fused together. It was then that I realized how many angry pixies were moving and how they were even angrier because of speed. The engineers behind EVs have a hard problem to solve, and I appreciate how far they've come, so far. When she charged my apartment's monthly power usage in 25 minutes... yeah those pixies are angry, and I was impressed.

Turning on massively large lighting systems with a more or less simple wall switch actually did make me curious how it could. Now i know!

So you're not "cut out" for one minute videos-big deal. Your 20-minute videos do a really good job of not only explaining how something works, but why it needs to work that way (or how it could work better.) And you make them interesting to listen to. I spent a decade as a corporate trainer, and I understand that's it's not easy to put all that together

why would i want a one minute video? your videos are informative, with the dry sarcastic delivery i crave.

I really do enjoy your videos. This one brings back so many memories. 1. Like when the contactor for the vacuum chamber exploded and threw mercury into the local environment (me!) To prevent contact burns some contactors use a simple plunge into a pool of mercury. Oops! 2. I once met a gentleman who used to work at Stanford Linear Accelerator (SLAC). One day he went outside because he heard a strange noise. Someone had forgotten to crank open the contactors in the beam line. There was a 6 ft arc coming from a piece of equipment into the local earth ground. Yes, arcing into the local soil with all the crackling, smoking and such that that infers. After some time the subsatation contactors opened to break the current. Apparently it was pretty spectacular. After that experience he thought that a career in retail sales of low voltage electronics was a probably safer choice. 3. At one laser manufacturer I worked at the assemblers of the power supply (15 kW) would sometimes wire in the large capacitors backwards. In test of the laser, that capacitor would heat up and there would be a steam explosion that would dent and deform the steel cabinet. Then the transistor pass-bank would arc out, causing the power company pole transformer to explode, and then they would come and lecture us on being more careful. Mostly we just learned where NOT to park - no by THAT pole. Such Happy memories!

I am so proud of you for referring to a meter which is set to current mode as a jumper wire. It can be hard to make people understand why current meters must always be connected in series with the load to prevent bad things from happening. Comparing the meter to a jumper wire gives the user a proper mind set as to what they are doing if they connect an ammeter across a source or a load. I think the ready availability of clamp-on meters these days is making life a lot safer for electrical workers and experimenters.

I had an internship at an electric company which mostly builds distribution cabinets for high power applications. They had huge contactors that had a wind up spring that when engaged slammed the contacts together. You could feel the impact in the floor you were standing on.

I’ve lost my house, family and friends right before Covid and WWIII began. To mentally survive, I retreated into UKposts, mostly educational or artistic content-like this. Just wanted to “interact” and show my appreciation for creators like you, thanks.✌️

I’ve been an electrician for about 35 years, and have done industrial, commercial and residential electrical work. I can’t begin to tell you how many contactors I’ve wired. These days, most things are being controlled over “Smart Systems” so that we can control them over WiFi or Bluetooth and they still use contacts! But your explanation to this audience I found entertaining….😊

There's a room where I work that has a normal light switch to turn on about a dozen massive light fixtures with 80 incandescent light bulbs each. When you flip the switch, you can hear the massive *ka-chunk* of the contactor from behind two walls a hundred feet away. I've sat there for more time than I care to admit just flipping it back and forth because it sounds so neat. Thanks for the insight into the mechanism!

I really appreciate how you make the effort to show where the wiring is coming from, going to and the route it takes. It gives a feeling of continuity (pun intended) to the circuit and why things are made the way they are made 👌

I worked at a electrical supply warehouse for three years and it was a maze of parts and cryptic part numbers without much of an idea what all of it did, outside of the abstract. I do often read articles to satiate my curiosity, but I didn't like working there, so it never passed the threshold of curiosity needed to find the articles. It's funny that years later I'm now learning what all those things I sorted and packed and catalogued actually do, thanks to you Technologically Connecting me back to the subject.

As a train guy, I appreciate the mention of just how absurd the early DC traction systems of locomotives are. You have a real knack for making this stuff interesting, and informative!

One of my favorite "contactor stories" was a discovery made in our computer center during a every-other-year power shutdown and maintenance weekend effort. A big UPS system was in the data center with a massive string of 2.25V lead-calcium storage cells in series for (I think) 432VDC @ 400 amps as input to the UPS system. A giant contactor was used for the EPO (Emergency Power Shutoff) for the entire computer room... red shutdown buttons on the computer room walls were in many locations to push should a major electrical issue occur. With all computers OFF, the big EPO contactor was being tested, and it ended up failing... it shut the power off fine, but it would not re-energize and close the contacts for the main computer room. Any place to get parts was closed. After a "hilljack engineering discussion", the contactor contacts were forced CLOSED with a piece of wood. All computer room staff were made aware of this naughty bypass, and where the manual power panel disconnect was located should a real emergency occur. Things ran this way for a few weeks until a new contactor could be ordered and installed; they somehow did it on the weekend and were able to isolate/bypass the contactor to replace it without another computer room shutdown.

"The recess created by the moving contacts provides a visual indicator of the contractor’s *current* state." I see what you did there!

I remember my work as electrical technician some time ago. Our mechanics had elevator from factory to warehouse, and they once did something funny and came to me asking for help. Elevator motor had two contactors, one for going up, one for down. Both had its coils connected via special NC contacts of other one, just to be sure no one tries press both buttons, up and down simultaneously, causing a short. So, elevator is on the first floor, refusing to go up. When up button is pressed, there's an audible humming and a bit of strange smell. I open the contactor box - everything looks just fine, both contactors intact, properly connected. I take my poking device, and poke the up contactor. Elevator goes up, no problem. I ask guys to press up button, and contactor is going crazy - loud humming, lots of sparks, elevator goes nowhere. I inspect contactor closer, and its coil is rated for 380VAC. I look at its neighbour - its coil is 240VAC. So the correct voltage was 240, and 380 coil wasn't strong enough to firmly pull in the links, so it was closing and opening 50 times a second instead, drawing LRA of the elevator motor, creating nice arcs and a bit of smoke.

I'm an Industrial Mechanic, contactors are probably the device I come into contact(pun?) with the most. Everything from driving motors on simple electric vehicles, to high voltage switch gear powering entire buildings.

Ohhhh now it's starting to click for me

ALEC!! oh, your hand disappeared in the corner... PORTAL!

I was absolutely stunned how easy you could pry that Eaton contactor! Here in Europe, opening such a thing up is hardly possible and usually requires destruction. At least, the types I've opened up where not at all made to be serviced and had to be destroyed up to a point you would not be able to use them anymore.

I enjoy the closed captions on these vids so, so much. I really feel like I really know which things go fwhoomp and CLACK.

The part of this video I enjoyed the most was the closed captioning @7:00 transcribing the sound of the AC unit starting as "[BRRGSHSSWMMMMAHHHH]". :) Excellent work.

I am once again astounded by this channel's ability to make a video on such a topic interesting, enjoyable, humorous and worth watching the entire way through.

As an industrial electrician, you did an awesome job explaining this subject. Bravo 👏

You have some of the only long form videos that I still watch. Thanks for the efforts.

@Technology Connections, hopefully you read this. Want to tell you that this channel and content has always been absurdly interesting and that it is because of you I learned more about engineering than I ever thought I would. Please keep making videos, I happily await each one to brighten our day!

HVAC student here, the single side shunt can sometimes be used to power something small at 120v reference to ground but is generally frowned upon

"Contact-or Not" is the greatest pun of all time and is my new energy for the remainder of 2023.

Literally, only you could make a relay so enthralling. I hope this comment boosts engagement.

Watching you explain stuff gives off chill teacher who doesnt take himself too seriously vibes

UPS technician here. Contactors are essential to a modern UPS, as well as a static switch, which is a solid state contactor of sorts.

I work as an industrial electrician, lots of times working with huge contactors from the 60s-70s. Super cool to see you do something like this man, great video!

I love the clarity I get from these videos on things I don't usually think about. My immature brain can't help but notice the very phallic sandcastle thou 😝

I've worked in industrial automation for about 10 years now, but my first job had me work near 4160 Vac cabinets... those contactors and fuses were ridiculous and gave me all the scares. Luckily now the worst I've got to deal with is 120 vac after swapping jobs. Long story short, I really appreciate this channel and have recommended some of the videos to my colleagues who are about as nerdy as me and the new guys because of how well he explains how certain tech works. Keep up the brilliant work!

16:30 “one of my favorite contactors” I doubt that phrase is spoken very often 😂

I'm an HVAC technician, specifically a reefer technician. I love all your videos

@TechnologyConnections, I RARELY leave a comment on any videos, but I was absolutely SO IMPRESSED with this one of yours that I just had to leave a comment! Been an electrical tinkerer for many, many years, (as well as a Network Engineer, PC Tech, Apprentice Plumber, Business Manager, Property Manager, semi-pro all-phase contractor, property flipper, semi-pro marine mechanic, and more, lol) wired up entire houses from new construction from the demarc-in to the finished project (adhering the NFPA 70/NEC of course!), troubleshot & repaired many gremlins in everything from typical automotive to large pleasure boats & yachts, fixed and repaired all sorts of things labeled "No User Servicable Parts Inside", lol, including large appliances, service panels, marine harbor utility, etc., etc. In short, I'm basically "The Fix-it Guy" for everyone close to me. This was a GREAT lesson on Contactors, something I haven't dealt with much, though I have dealt much with their little brothers, solenoids and relays much. You did a FANTASTIC job of explaining, with clear simple language and excellent sharp video (I paused and rewound many times to read the labels for a deeper understanding). I love your style of dry-humor-meets-Mr.-Wizard, your always excellent footage, and how you have the ability to not just narrate but to EDUCATE, and your use of analogy is excellent to help people grasp ideas and concepts they may not be familar with. I can only assume you're so popular now that YouTubing is your "full-time job", but if not, or if you ever wanted to reinvent yourself, you have such a great manner and demeanor that you would make a most-excellent professional clasroom teacher; one who not only cultivates but who INSPIRES. I mean that with great respect, as I always say, "There is no greater profession in life than to teach or to heal." Anyway, been a follower for a few years now, always appreciate your content, and I hope it's both lucrative and fun. Keep up the EXCELLENT work. It's hard for me to say this because I have never found fault in your productions, but somehow, in a way I can't put my finger on at the moment, your work has improved, and is some of the very BEST of UKposts. Perhaps you're familiar or not, but you reign supreme alongside some of the BEST tech channels/creators I have discovered and follow, South Main Auto Repair LLC, Project Farm, Torque Test Channel, etc. Can't wait to see more of your excellent work. 👍

Very timely! I just had my HVAC go non-functional because of ants getting up into the contactor and preventing the circuit closing. Now I have a name for the device that the HVAC guys wanted to charge me $300 to replace, even though a bit of canned/compressed air is "good enough" to clear it. Thanks! ❤

Note: a big advantage of solid state/semiconductor relays is that they can switch an AC voltage at its zero point. That is, it can watch the line voltage reach zero in the cycle, and switch at the zero point, effectively breaking the circuit when there is no current whatsoever flowing.

I'm so glad you're putting up these videos. I'm a control systems engineer who works with this stuff a lot, but I've never known the inner workings. I knew a fair amount (since this is my field) but you still managed to teach this old dog some new tricks. Thank you many times over.

Thanks for not making it short! 1 minute is not enough for a good informative video.

As someone who works with industrial equipment it is indeed very satisfying to be able to just press a small button and hear a nice clunk as the equipment powers on (in our case the contactors are powered by 24V, which is under control of the safety system, if the safety PLC detects an error you won't get high power)

Those lighting contactors make a really nice 'thump', when they pull in! For high current loads, the old mercury contactors were very reliable. Obviously, mercury presents a few issues, but it did reduce wear. Also, a VFD video would be awesome.

When I bought a Spanish house with a pool (with pump) I had no idea I would be watching these kind of videos! But I love it.

you explained the function of a light switch so elegantly

One problem with these contactors in HVAC equipment is that bugs or other creatures can crawl in between the contacts and prevent proper functioning. I think the older ones used to be more open, but newer designs have put more plastic around the contacts.

Who wants a one minute video on contact us. 25 minutes is perfect, lots of detail and always super interesting. I live for your posts!!!

Fantastic video! I work with lighting controls, and contactors are something we design with every day (using our system to add a "brain" to them), and there are often large panels full of multiple contactors we interface with. Some of our newer team members have had trouble with the concept, so I'm definitely going to be sharing this one with my team!

HVAC Tech here. The Rated Load Amps for your compressor is actually the maximum it is rated for during run time. Typically, it pulls 45%-60% of that load on regular residential manufacturers (lennox included) ((at least down here in Florida)). If our company performs regularly scheduled tune ups over the course of 3 years, we can actually tell if there is an undercharge or overcharge of refrigerant with the Actual Load Amps of the compressor (or if your motor is going bad, which is usually the case if it suddenly has more Actual Load Amps than it normally had over its history without us charging your system with refrigerant). The reason why is because less refrigerant means it has to make smaller compression ratios with the same amount of torque(?), AKA overcome less resistance, and vice versa for more refrigerant. The Blower Motor depends on what speed setting it is set to. The fan motor will normally run at 85% to 95% of its RLA. edit: oh!~ you covered this at 19:35 ! neat! that's why I should watch the whole thing before i go and blabber haha

The star/delta configuration described at 15:59 reminds me of series/parallel controllers found in old trams and electric trains! To start from a stop to low speed the motors are wired in series so they split the voltage between them, preventing the motor coils from burning out, then when getting up to speed the controller switches so the motors are in parallel and get the full voltage each to safely run at higher speeds. EDIT: you briefly mentioned DC train control after I wrote this comment :)

For the hotel example, if the items and their breakers are spread all over the building then it will mostly have several different contactors (usually one per breaker) and all the contactors are operated as one from a central control circuit. You could run hundreds of contactors from one control circuit spread across many different breakers in many different locations.

Took s few coklege classes in this for my ME degree, and after having worked in a shop setting with alot of heavy equipment and regularly changing out broken contactors, wye delta starters, and programming VFDs, i can say i really appreciate this video

Thank you for finally explaining what the actual difference is between a contactor and a relay. It's something I've asked people several times before, and never been able to get a straight answer.

I appreciate the effort to properly subtitle the blooper reel with the actual sounds produced.

I’ve never heard so much discussion about which color wire does what since the last time I saw a movie about bomb disposal. Now that I think of it that would make a great episode on this channel.

I love the long form videos, it’s cool to see the entire breakdown

Good job of explaining contactors! One minor thing I would add is that they are useful for even low loads when the switch is far away from the line that feeds the load. Having a contactor helps to reduce voltage drop by shortening the wire length needed from line to load. I use this approach to power my pool lights, for example.

I just love this channel so much. I love learning about stuff that I would never even ask myself how it works. I love your writing and your jokes and the way you deliver them. Just great. Thank you!

We like the long form video essays, or at least I do. I love listening you talk about a topic for an hour!

It's always exciting when you overload a contactor and weld the contacts closed. You have to work fast to catch the magic smoke. Thanks for sharing!

I came home from work one day and it was 26 degrees in the house. My wife "Yeah, it's been warm all day". I rush downstairs and find that my hot-water electric boiler was running full out, over temperature and over pressure. Immediately switch the breakers off and bleed off some of the excess pressure, then find that the contactor contacts had welded themselves together. I also replaced the safety valve before starting it again.

I love how you explain things so simply and with plain language. It's very accessible without being condescending. Very well written. Great job! Keep up the good work. I learn a lot on your channel.

"through the magic of buying two of them" is now recognized as a catchphrase

Right as me mentions the switch noise, the banner for Switches Are Clicky pops up in the corner. Ahh how satisfying to us geeks. YES! WE WANT MORE!

I was hoping for the day you can fully explain contactors. Its something i was fascinated when learnt from them on school and its nice to show appreciation for one of the keys of analog automation for electric systems

Fun Fact about computers: - In the old AT design, the Power Button directly switched the main voltage wires of the power supply. - But in the ATX design, the power Button switches a relay on the motherboard, that in turn switches a connector in the PSU. One advantage is that the computer can turn itself off after shutdown (AT ones could not do that). And once you add a bit of Standby Power, we can have features like "wake on keyboard", and even "wake on LAN".

Great to have a detailed breakdown of the intricacies of something which seems simple on the surface, cheers!

I'm glad you made a mention of contactors for rail equipment here, high current DC comtactors (particularly those used to control energising catenary wirres) are huge and demand respect.

For some weird reason I absolutely love the sound of automated relay/contactor clicks. There's a detailed video of KITT's scanner (Knight Rider) out there where they put the camera up to the control box, and if you know how fast KITT's scanner scans, you can just imagine the sound of the relays going.

I'm an industrial I&C engineer. Solid information.

Nice video. I always enjoy your in depth analysis of whatever the subject matter may be. Never stop doing what you do. Some of us greatly appreciate it.❤️❤️

Would not have imagined there was a whole video's worth of content on contactors!

Great timing! I'm making a UPS system for my friend that swaps between normal and backup power without the UPS needing to provide full power, especially in normal operation. It removes a few advantages of the UPS like power filtering, but it can be mitigated with external solutions for a fraction of the cost of a larger inverter. His house grid is a three phase system, but I've decided to only power two of them in the case of an outage by splitting the output of the single phase UPS as there are no multiple-phase appliances in his appartment to suffer from that and one of the phases powers only things (clothes dryers, washing machines etc.) that aren't really prefferable to feed from valuable battery storage. Contactors are pretty much the best way to do that and I love them.

Thank you for another exceptional, entertaining, and educational video on something that I didn’t know existed before. It certainly didn’t feel like 25 minutes (meant as a compliment) and I would have enjoyed you to continue going on for longer. I got the feeling that you have more information about the topic but realized the length of the video and jumped to the conclusion. I understand that not everyone likes very long videos and that’s why you may have done it that way. Your work is greatly appreciated.

Thanks for relaying this information, I'm normally open to watching your videos as they keep me current on interesting topics from pole to pole.

Love your videos man! I’m an electrical technologist for a gold mine in Canada and you really know your stuff, you obviously have an electrical background. I wish more people in our electrical department watched your videos, they could really use this information!😂

As an industrial automation, and maintenance technician, this is a very good video for new guys in the field. I love UKposts. Thanks Alec!

Thank you for explaining the difference between a relay and contactor as that was one of the first questions that came to me when you started describing them.

I really enjoyed this one. I recently wondered why my Honeywell T9 indicated that is was waiting on equipment, it has been running hard. This gave me a perfect answer. Your videos are ALWAYS good!

I love your jokes and how you go in depth into each topic! 20 minute mark, I would sit through a 20 hour seminar if you were giving it!

This was increadibly cool to watch for a nerd such as myself. I am now that much more informed on the various electrical systems out there. Thanks!

I've never heard of people like me who love the sound of contactors and relays. It's so cool to me.

It's so interesting watching this channel and seeing the blackbox of technology opened up. A lot of what runs our everyday lives is surprisingly simple

As a British Electrician/Plumber/Massive Nerd, I do find the videos where you give description of your heating systems quite fascinating. Your ducted gas furnace systems with in-line aircon evaporators, are essentially a scaled down version of the AHUs we use for commercial premises.

I smiled when you pushed that in to manually override. We've done fun stuff like this... except, moving elevators up and down without the logic being aware in the slightest. (more older models however) :D