As an Electrical Engineer, you did a great job explaining.

I’m a EE myself, and I wish I could have had James explain this subject to me 40 years ago when I was at Penn State learning it for the first time. Very straight forward and clear. Thanks for making a mind twisting subject simple!

This is the best description I have seen to date on 3 phase power configurations! Your explanations are clear, concise and easy to follow! Thank you!

James, After last week when you replied "only when referred to neutral" I replied "yea Duh" and walked away thinking "how is he going to explain this to everybody else that is not an engineer?" As an electronics engineer I am biased , but I must say that I think that you did an incredible job in describing what is going on with just the right amount of math so as hopefully not to overwhelm most people. And gathering the information, scripting, shooting/editing the video in less than a week in itself if quite an accomplishment. Have a Great Weekend and try to stay warm. By the way, How do you keep your shop/garage warm in the winter?

As an electrical engineer who understands this stuff your explanation is superb. I wish I had videos like this 30 years ago, they didn’t explain it well back in the day.

Thank you for making this video. I've had three different people try explaining this to me and I just could not understand how it worked. Even asked Big Clive to make a video explaining it. This explanation is the first that really makes sense and I appreciate you taking your time to put this together. It's just been hand wavy black magic until now.

Clear, concise and easy-to-understand explanation, James. My formal education in the electrical branches of Physics & Engineering stopped with DC circuits, and in my professional life as a ChemE/Process Engineer/Project Manager I left things to the EE's (I can still remember the EE at one of the plants I worked at getting very upset when I lifted the starter contractor on a 200 Hp motor because I didn't want to go from the outside starter stack at ground level to the third floor to hit the start button - even though I was using an insulated screwdriver).

I decided to do something I had never done before, to congratulate someone for an exceptional video. When I started watching I thought it would be a thankless task, but the end result was perfect. This subject is something that many professionals in the field still do not understand!

Thanks so much, I never understood this. Your explanation was well prepared and presented with clarity.

Center-tapped single phase residential mains does *not* have two legs 180 degrees out of phase from each other. It is a *single phase* supply so there is only a *single* wave. Since there is a center tap, that allows us to measure half of the *single* wave (from L1 to center/neutral) independently from the other half (from center/neutral to L2). Note the order in which I mentioned those: *L1 to N* and *N to L2* ... That minor detail is significant. Most oscilloscopes are ground referenced and you are therefore forced to measure from *N to L1* and from *N to L2* so you are measuring one half of the wave *backwards* from the way you are measuring the other half, so they *"APPEAR"* 180 degrees out of phase but they are *NOT* and cannot possibly be. A wave cannot be 180 degrees out of phase with *itself* . It is critical to keep in mind there is *only one wave* and the two traces on you scope are two halves of it. A Rotary Phase Converter does not take two waves which are 180 degrees out of phase and turn it into 3 waves 120 degrees out of phase. It takes a *single* wave existing between two points, adds a 3rd point, and the result is the creation of two new waves between the original two points and the new 3rd point, and the 3 resultant waves are 120 degrees apart. You can run a RPC from from a single phase 240V source which isn't center tapped and has no neutral. If there's no center tap, no neutral, no "180 degrees out of phase" legs and the RPC still works, then all this discussion about neutral and the 180 degrees out of phase waves was extraneous.

Man I could have used this video about 4 years ago. I built a rotary Phase converter from scratch very challenging but a great project. I purchased a 3 phase 40 taper mill and needed the power to run it in my shop. After buying 20 hp slave motor, another panel, a box a bunch of capacitors, contactors and a few other bits it was mostly education. I found it very interesting and rewarding to get mine build and running. every time I start it up it makes me smile. This was a very good video thank you!

Yep! That explanation cleared up my confusion that I have had for over 70 years. It is obvious to me now that whoever I asked before had no idea how it worked. Thanks! It is surprising how FACTS clear up confusion in a blink of an eye.

This is excellent! I work in the HVAC field, though I’m pretty much residential, occasionally I do work in commercial applications and deal with three phase. I never understood how three phase could exist. This video explains it perfectly. Im also a hobbyist woodworker, and I worked in a machine shop in high school. I love seeing a block of steel come in and leave as a finished product.

That was far better explained than I could have hoped for. Thank you!

I love these detailed breakdowns, thanks for doing this! I'm going to be diving into my own three phase adventure when I start setting up my Deckel FP4A CNC mill and having a solid foundation of theory like this is going to be super helpful!

What makes this video so great is your ability to establish proper context. That is something many videos even school teachers fail to do. 100% On This Video! I learned something new about voltage that I did fully know or grasp until now and I already have a fairly decent understanding of circuitry. I had an understand of what 2 and 3 phase power sources were and the difference between 220 and 110 and could wire up most electrical devices with minimal issues, but to fully grasp the differences between to different implementations I now understand it much more clearly now thanks to you. This is the first time I've been impressed at this kind of level in a while. The last few who have impressed me like this is when I came across Ben Eater and 3 Blue 1 Brown. There's a few others too... This is my first time coming across your channel and the first video of yours I've watched and it has earned a sub! If the rest of your content is anything like this I can count you among those that I mentioned. It's more than just the topic, but it's also having proper context with the ability to explain it in a clear, simple and precise manner along with a great demonstration. Job very well done!

Very nice review James - thank you! I have built many DIY router tables, purpose built CNC machines and have integrated several of the over-seas water cooled 2.2KW spindles with the accompanying VFDs. The conversion to or use of 3 phase (via the VFD) in my 50's home (upgraded electrical a couple of decades ago) puts a smile on my face every time I fire up the CNC router to mill a carbon fiber panel or part for a project. I have yet to work with rotary phase converters. I'm learning a lot and have the rest of my life to learn more. Love the backed out screw to hang your DMM - very cool brother! Keep it up...

I was VERY cloudy on how this worked and you did a GREAT job of clarifying it for me. I somewhat more understand it now. Thank you.

This is an *excellent* video. That said, the first thing that comes to my mind to answer the question of "how can it create 3 phase power from split phase power" is, "because it's rotating". If it's rotating, you can generate 3 phases, exactly the same way they make 3 phases at the power plant! 😉

I enjoyed the video. I have no electrical credentials but have built a couple of rotary converters from salvaged motors that have worked satisfactorily. I have one in my home shop that has been in use for twenty plus years. Your explanation actually is reassuring since there is much negative information out there. Thanks for sharing!

My hat is off to you. You are the first guy I have even seen to explain this correctly. I have been building rotary phase converters from scrap motors for many years. While I have always known the answer to the question, I have never seen anyone other than you explain it from the reference of a high leg delta configuration. The hardest part is balancing the voltages on the phases. I do this with capacitors. But you get trouble with matching loads. A friend of mine showed me a cool trick. He uses balancing capacitors at each load. This maintains the most consistent voltage over various load conditions.

I wondered about how that third leg fit into 3 phase as well! Thanks for putting the scope on it, because I never got around to it!

I am not any kind of engineer, except amateur. This is the first explanation of 3 phase power, out of many I have watched or read over decades, that makes sense. Thank you for FINALLY explaining it in a way I can actually understand! You rock!

Great explination!!I have built several phase converters both rotary and static.I started long before the internet when information was hard to come by. I learned what worked by trial and error. It always botherd me that the generated leg to ground was much higher voltage. In function it didn't matter though because the phases relative to one another were balanced. Thanks again for clearing up the mystery!!

There's a mistake in Figure 3 at +11:45. The arrows for two voltages on the both point to the same legs (A and Neutral) but the first one says 240V and the second says 208V. The one one that says 240V should point to the A and C legs, not the A and Neutral legs.

Probably the best and most throughly explained video on rotary phase converters. I am a residential electrician but am familiar with three phase power. In rural settings I have seen three phase power distributed to farms in the form of open high leg delta (one large and one small transformer) with the meter on a pole in the barnyard between the house and outbuildings, 120/240 single phase ran to house and 120/240 3 phase ran to outbuildings that require 3 phase for the milker, auger/conveyer, grain dryer or other large motor loads..

As an Electrical Engineer You Sir Have Done an Amazing Job Breaking Down 3 Phase Wye and 3 Phase Delta in This Video 💯💯 (And Differential Probes are a Must)

This is a mystery I always questioned and wanted to understand. THANK YOU! Great RPC and 3 phase explanation.

I've been an industrial electrician for five years, and this video FINALLY helped me really grasp how rotary phase converters function.

I’m an electrician in the UK, I think you did a great job of explaining the physics and definitely improved my understanding, thanks for the great videos 👍

Nice explanation and the images made it easier for the masses to understand. I'll share your video next time someone asks about how three phase works. I did a lot of research before I purchased my phase converter and realized the average person who owns three phase equipment has zero concept how this works. I'm fortunate to understand these sort of things as I read about them and have access to a few commercial electricians to separate the wheat from the chaff when I had questions or found conflicting internet based information.

This is by far the most informative single video that I have seen on this topic. Thank you!

This is by far the best explanation I have ever seen on this topic. Great job James.

I started watching this video when it came out, went OH OH OH after the intro, fired up some graphing software and worked it out for myself. You inspired me to learn the way I learn best. Just watched the rest of the video, and you do an excellent job throughout.

Nice job explaining that James. Y/wye 3 phase connection is more commonly called a Star connection here in the UK. Neutral taken from the centre point of the star, and is ~0v As most may already know, the direction of a motor can be changed by transposing two of the phases. Also, a 3-phase motor can run on just two phases if for some reason one leg is disrupted (blown fuse, broken connection), but this will cause the motor to overheat with reduced power output. It's always worthwhile to know how warm to the touch the motor runs in normal use, and check periodically. Reduced output can go unnoticed.

This is just so good. I've believed for years that the third synthesized phase was a "close enough" approximation to 120 degree symmetrical 3-phase. This opened my eyes!

As a clueless noob with a bit of electronics and electrical background, I have always wondered what the difference was between a wye and a delta and why there was a difference AND what use they would be "in real life". This video was massively useful and now I understand so many things I had only guessed at in the past. Thank you for the clear, simple and concise description of what's going on.

Good explanation James, I'm originally an electrical engineer myself, I couldn't have done it better. Although an expensive explanation: 3 isolated differential amplifiers. Appreciate this.

This was an excellent video and the way you went about both explaining the theory and then showing it in practice will definitely help people. I personally appreciated that you pointed out in tactful and non disparaging way the pitfalls and how you can measure it "correctly" but get the wrong answer because you are measuring in the wrong context.

This is a substantial topic Excellent work and view . Thank you.

Thanks, James, that’s just what I was looking for! A lot of cobwebs have been cleared out. 👍

Thank you so much for the explanation! I'll be watching this about 100zillion more times over the next few years. I'm not electrically savvy, so these simple straightforward explanations are gold. Excellent!

James, I love this content and all of your videos. Outstanding.

Just wanted to take the time to say that I am not an electrical engineer.. and I fully understood your explanation. You are an excellent teacher

FINALLY! I have two degrees in Engineering (not electrical obviously) and have made components for power transmission. Like Dennis the Menace I ask everybody this question. One guy was a PHD in physics and couldn't answer. Your explanation was wonderful. I have been running a machine shop off a RPC for 20+ years and always wondered if the huge bank of capacitors somehow moved one phase. Now I understand...nope, they are start and run only. Thank you so much! Keep up the great work.

As I 4th year electrical engineering student, you did an awesome job explaining it, I didn't know about the dog leg delta config.

Seems like you've drawn out all the Electrical Engineers with this video, but I'll say it again, this is a damn good explanation of RPCs. I especially like the casual flex of having three of those differential probes haha

This is the best video I've found to explain how a rotary phase converter works. Thanks.

James, fantastic explanation, thanks so much. Its such a fascinating piece of equipment, I actually never knew such a thing existed until your first video about them. I work with electronics, some of which uses 3 phase power and so all the theory here made perfect sense to me, but putting it all together in this was was awesome.

Very well done. Had been wondering exactly how this worked and now I understand it. Thank you!

BRAVO! Finally an explanation of where the "wild leg" that "some machines don't like" story comes from, and a model of wye, delta, "wild leg" delta, that one can understand!!!

Great explanation. EE here but it's been a while since I've dealt with three phase. This got me caught up real quick.

Thank you for taking the time to explain this. My previous 1950's era welding shop makes so much more sense to me now. Dominion power called it bit©h leg vs. Delta when they would come out to tighten the main lugs or replace fusable links lol.

Excellent ! Clear concise explanation and -as always- a great presentation. Thx

I had an incorrect mental map of phase conversion. This really broke phase conversion down very well. Thank you.

My shop has an open delta configuration to the grid. Im a mechanical engineer and this configuration has blown my mind from day 1. We run 10 Haas VF2SS with 2 5 tone air conditioners in split phase. 2 air compressors in 3 phase. I’m always amazed the the wires don’t fuse out feeding our building. Somehow this works. I added solar to my building to help boost the split phase aspect. Again I don’t know why this works but it does. I will now go crawl back into my hole.

Great discussion and reference slides

Yesssss, I was waiting for a video about this. Thank you!

Excellent presentation. I use two rpc in my shop. Trouble free. Thanks for taking the time to share with us. TG

James, Last week I asked for this explanation of the “phantom phase”. You succeeded far beyond my expectations. I feel somewhat guilty for having caused you to buy the fancy probes. But I don’t feel **too** guilty, because now you have another cool tool. 😊 Excellent explanation. Detailed without fluff. The point about reference voltage was the insight I needed. Thanks for all your KZfaq work. I get lots of ideas from you (which causes *me* to spend $$ on tool tools). - Retired embedded software engineer.

Hi James, I'll add to the congratulations. Also, thank you for referencing the diagrams to North American practice. Many KZfaqrs seem to forget that they have a global reach and things can be very different outside the US. Sometimes potentially lethally so. For those who don't know it is nor just voltage and frequency, for example the externally incoming UK supplier provided earthing (linking to the interior protective conductor) arrangements are a subject in themselves and serious mistakes can be made here by not being aware of their complexity.

Absolutely wonderfully explained!! Great job James.

Excellent explanation. My experience with rpcs is that they work well with predictable loads, but when you use them to power modern cnc equipment, the generated phase doesn't like large dynamic loads. It would interesting to scope your rpc while running a very dynamic load like a lathe motor.

Wow! Best explanation ever of three phase power and it’s different configurations. Wired my shop using phase perfect which is a digital 3 phase producer that is always on, quiet, better 3 phase than available from the power company and only a 2% loss of power.

Straight forward approach James! Thank you

Thank You, cant tell you how many arguments I have had over this. I ran CNC's for years with no issues (done correctly that is)

As always... I enjoy your presentations that deliver the simple truth about a seemingly complex subject. Having a background in three phase four wire 208v, I really appreciate your concise explanation. I knew that I know this stuff but could never explain it as clearly as you have just done. I will, of course, have to plagiarize this at some point in the future.

Exceptional description very well done

This was an excellent explanation/tutorial. Thank you for sharing.

That was brilliant James. You have a great ability at explaining complex theory. I am a semi retired Electronics Engineer so I did know this, but your explanation was excellent revision! :)

Good information thank you for sharing . It's been a topic of interest for some time.

Thanks for the explanation, I've never had had a hands on with high leg delta yet but if I do in the future now I'll be prepared.

James, Like many of us out here watching your postings about electrical stuff....I am of the.... plug it in hope it works and I dont get zapped mind set...YOU and you alone here in You Tube World, take the time in all you do and explain things in much easier to understand laymen's terms so that us real world folks aren't so confused and overwhelmed with all the techno jargon and mumbo jumbo. Thank you for sharing your extensive knowledge and experiences, you are a fantastic TEACHER and long overdue for glowing accolades and recognition of your talent in doing this. You may be an EE by profession... but you are really a Teacher and mentor at heart. THANK YOU !!!!!! Don

great explanation! I worked as a motion picture lighting guy and when I started working in LA the studios were 2 leg DC using a giant motor generators to generate DC from 2300V 3 phase. As we started to have more AC only lights the studios scrapped the DC plants and went to 208 3 phase. It was an interesting time as mosst of the union lighting guys had never worked with large AC systems. In non-union production we had only worked with single, or 2 phase systems, so it was an easy transition for the non-union guys. The big problem was when we had start following the National Electrical Code which was administered by the LA Fire department. Lots of stories about those interactions.

Much better explanations than many others I watched. many thabks

You did a great job explaining that. I wish my old EE professor had done it as well...

I didn't understand all of this, but it did answer the question I have had and that is about the 120 degree phase difference. Thanks!

I'm really glad you posted this video, great job. High leg delta sums it up well. There are many bad phase converter videos and comments on line, too many videos arguing that it doesn't make proper 3-phase, or with people adding all kinds of capacitors to "balance" the system. I wanted to make a video like yours a while ago, but don't have a channel. This might not help non-believers, but below is the engineering math behind it showing that it works. Warning, a lot of engineering math ahead! First we need to set up the equations. As stated in the video the power lines are 180 electrical degrees (pi radians) out of phase at 120 volts, call them L1 and L2. In the 3 phase AC motor being used as the rotary converter, the voltage that is induced in the third phase (L3) will be 90 degrees (pi / 2) out of phase from L1 and L2, with respect to ground, and it will be around twice the L1 and L2 voltage (with respect to ground) due to how the windings in the motor interact. If the line to line voltage are measured (L1-L2, L2-L3, and L3-L1) they are all around 240 volts, and if you look at it with an oscilloscope they are 120 electrical degrees apart. Let's get into the math.... These are the output waveform that are wanted: 339.4*sin(x), 339.4*sin(x - 2 pi/3), 339.4*sin(x + 2 *pi/3) Copy and paste the above line in the Google search bar and you should get a 240 Vrms AC 3 phase graph. Let Google graph it for you! Now, to get that waveform from a rotary converter and 120 Vrms AC split phase power, here are the equations for line voltages with respect to ground (angles in radians not degrees, 180 degrees = pi radians), the two 120 Vrms AC input waveforms (L1 & L2) and the 240 Vrms AC waveform generated in the converter (L3), 90 degrees (pi/2 radians) offset from L1: L1=120*sqrt(2)* sin(time*60*2pi - 0) 0 electrical degrees offset, 60 Hz, 120 volt line to ground L2=120*sqrt(2)* sin(time*60*2pi - 180*pi/180) 180 electrical degrees (pi radians) offset, 60 Hz, 120 volt line to ground L3=240*sqrt(2)* sin(time*60*2pi - 90*pi/180) 90 electrical degrees offset (pi/2 radians), 60 Hz, 240 volt line to ground Let's simplify those equations a bit, and set x = time*60*2pi, to get the three line voltages (wrt gnd), offset in radians: L1=169.7*sin(x) L2=169.7*sin(x-pi) L3=339.4*sin(x-pi/2) Google search the follow line for a graph of L1, L2 & L3 (copy and paste into Google search box): 169.7*sin(x), 169.7*sin(x - pi), 339.4*sin(x - pi/2) To get the line to line voltages, take the difference between two lines: "Line to Line equations (1)" L1-L2=169.7*sin(x)-169.7*sin(x-pi) L2-L3=169.7*sin(x-pi)-339.4*sin(x-pi/2) L3-L1=339.4*sin(x-pi/2)-169.7*sin(x) Those equations are for properly spaces 3 phase 240 Vrms AC power, separated 120 degrees (2 /3 pi radians). Google search the following line to get the graph of the 3 phase voltage: 169.7*sin(x)-169.7*sin(x-pi), 169.7*sin(x-pi)-339.4*sin(x-pi/2), 339.4*sin(x-pi/2)-169.7*sin(x) The equations can be further simplified with some mathematical relationships (look them up if you want to verify): sin(x)-sin(x-pi) = 2*sin(x) sin(x-pi)-2sin(x-pi/2) = 2*sin(x - 2*pi/3) 2sin(x-pi/2)-sin(x) = 2*sin(x + 2*pi/3) Apply the relationships to the "Line to Line equations (1)" to get: "Line to Line equations (2)" L1-L2=169.7*sin(x)-169.7*sin(x-pi) = 339.4*sin(x) L2-L3=169.7*sin(x-pi)-339.4*sin(x-pi/2) = 339.4*sin(x - 120 pi/180) L3-L1=339.4*sin(x-pi/2)-169.7*sin(x) = 339.4*sin(x + 120*pi/180) Google search the following line to get the three phase 240 Vrms AC graph: 339.4*sin(x), 339.4*sin(x - 2 pi/3), 339.4*sin(x + 2 *pi/3) The math shows that the line to line output voltages from the rotary converter will be 120 electrical degrees out of phase, at 240 Vrms AC. If you want to substitute back in for x, the input and output are: 169.7*sin(x*60*2*pi), 169.7*sin(x*60*2*pi - pi), 339.4*sin(x*60*2*pi - pi/2) 339.4*sin(x*60*2*pi), 339.4*sin(x*60*2*pi - 2 pi/3), 339.4*sin(x*60*2*pi + 2 *pi/3) Easy!

Electrician here, you did such a great job with this one! I learned a lot. I guess it was a misconception of mine that the sine wave would look so good, I thought that the manufactured phase would be lagging, at least before the power factor capacitors, but of good enough quality for motors, the oscilloscope convinced me otherwise. Thank you for a great video.

Superb explanation, clearly delivered, THANK YOU. You just earned a sub.

Nice treatment of a confusing subject. Cleared it up for me. After 70 years. Thanx. :)

By far the most helpful video I have found yet.

I always wondered that. Thank you for your marvelous explanation.

In some parts of the east coast, High leg delta is pretty common from the utility. It sure is frustrating when you don't understand what it is, but this made it much clearer why you might want that.

This is a very difficult topic to explain. Your video did an excellent job and explaining how this actually works thank you

good video. i'm glad that in germany we have a three-phase network that reaches almost all apartments and houses. but it is interesting for an electrician to see the difficulties that arise when one does not have such a luxury.

Great demo, well done.😊😊😊😊

Excellent video. It’s important to be very clear about what a phase is. The reason your residential split phase voltage waveforms are 180 out of phase is because they are the same phase, you are just using the center tap as a reference point. U.S. residential services are single phase. Two phase power is a whole different system (3 or 4 wire 90 degrees out of phase). As an electrical apprenticeship instructor these are misconceptions were constantly battling. Again excellent job

James, what a crystal clear explanation. Chapeau!

Excellent tutorial and explanation James. Thank you.😎

Beautifully explained. Nice job.

James, Excellent job of explaining this! "Reference to neutral" was what I was missing in my understanding.

Very good explanation, James. Thanks.

Loved that, great explanation.

Thanks James, good explanation of how the third leg is created and the "wild" delta that results. I am running both home made rotary and capacitor phase shift starter converters in my shop. Using 2 old relays and proper capacitors it is easy to build a rotary converter using any 3 phase induction motor with the correct voltage taps. Just remember a 3 phase motor rated at 10HP will only produce about 6HP as a phase converter with only 2 of the 3 wires providing power. If you only need a lower than rated torque from a 3 phase induction motor you can simply give the 3rd leg a phase shift from a capacitor to start. A optional smaller run capacitor on the 3rd "wild" leg can be used to improve the power and balance the 3 legs. Another little known fact is, once a 3 phase induction motor is running, it will continue to run if one leg of the power is disconnected. A 1/3 power drop will result in the maximum load with the missing wire. Be careful not to stall a 3 phase induction motor running on 2 wires of single phase!

Great explanation. With the introduction of VFDs, more choices to which one to use. I am guessing that with a properly rated phase converter, you could have multiple machines on it. The VFDs are motor specific but offer more control of the motor. Of course, there's the issue with your motor while using it with a VFD. Turn down ratio. Most general duty 3 phase induction motors have a turn down ratio of 10:1. Inverter duty motors are usually 20:1. You can get 1000:1 if your budget can managed it.

I'VE BEEN WAITING FOR THIS FOREVER

Beautifully done.

Brilliant presentation. I wish I could explain it this well, but now I don't have to. I just send them the link to your video. Thank you so much.

..... I'm not an EE....but built my 10hp rotary phase converter roughly 15 years ago, which has thus far worked flawlessly in powering 5 different 3ph machines. Although the build was successful, I've often wondered & never understood how this worked until now. Thanks!