Explanation of the phase relationship between the two transformer secondary windings, or two halves of the winding, feeding a 120/240 V Single-Phase system.
At 74 years old and been working in an electrical environment for more than 50 years I have never seen a good explanation like this. Would have loved to have you as my tutor. Keep the videos coming.
the biggest issue is arrogant electricians.. the teachers (typically former electricians int he field) will want to "skip" over stuff, to appear to be "macho" to the guys from the union or for those working in industrial. He will say stuff like "I know you guys know this stuff so we can run through this part, but if you dont raise your hand". therefore making it a matter of ONE guy looking "less of a man" for raising his hand. AND DONT LET that man be a minority among a bunch of white men.. because then theres a DOUBLE whammy feeling. the white guys looking upon you as if youre stupid. this is why teachers need to be TEACHERS ... like this man is doing.
A most unusual video where the explanation was unique and a credit to the Dave Gordon. I have never seen the concept of vectors addressed to the non maths audience in this fashion with attention to detail . You sir are a credit to your profession.
But wrong conclusion.. . He failed to identify the correct Reference point, which is and has to be the Zero or Neutral point. . . . Looks as if he sort of used the paper as his reference. . . . Paper does not carry electrical current, wires do, so you have to use the correct electrical point, which is the Zero or Neutral point.
Apologies if this adds some confusion but just trying to add some clarity. Let’s start with the basic single winding you are showing as the voltage source and let’s look at it without any mid-tap, center-tap, neutral, or split-phase tap connection. i.e. Just the winding. In reality this is a winding as part of a transformer, possibly your home or business pole or pad mounted transformer. If we can agree that this winding is receiving its energy as a secondary winding to a primary winding, which is being fed from a generation source, then it would seem that our interest in labeling any of the downstream, secondary wiring as “in-phase” or “out-of-phase” should always be in reference to any of the other transformer primary windings. With this approach, I am looking at our common electrical power generation and distribution system, where for example, the hydro-electric plant’s generator creates voltages via 3 distinct windings and because the armature is rotating across these 3 windings at different times, we have 3 windings which are physically arranged to be producing voltages 120 degrees (1/3 of 360) from each other. These three windings are then tied together in series, or some would say in a delta connection with three tap conductors to be extended out through various control and distribution apparatus to our local pad or pole mounted transformers. And back to my point, it is these conductors that will impact on our reference to phasing, or as we commonly label - A Phase, B-Phase, and C-Phase. My own education has me of the understanding that our commonly used system of 120/240 volts is simply a secondary winding of a local utility power transformer, which is being induced with a 240 volt voltage from a primary winding being fed from 1 or 2 of these original hydro-electric source conductors. And I include the possibility of 1 source conductor simply because in some cases the primary voltage to our local transformers may just be a primary winding utilizing one source conductor and a common grounding tie with the secondary. So when I look at this discussion, I tend to disregard references to phasing within any of the secondary 120/240 volt wiring because to me the phase of this wiring is linked to whatever source conductor or conductors are used to power the local primary winding. Yes, you could have true original source phasing within the home or business system, but it would be because the 3-phase power has been brought in and is fully utilized to power a 3-phase transformer which in turn has 3-phase secondary windings, possibly delta or Y connections. Having offered this, I also acknowledge the ability to engineer electrical phasing to operate certain 3-phase equipment. But when I read the original question Dave put out there, relative to the AC sine-wave(s), I just immediately assume it is in phase due to how the 240 volt secondary winding is powered. And I am still open to being re-educated as to how to look at phasing. I do also understand that when we want to refer to either side of the 240 volt power source, we tend to say the “black phase” or the “red phase” or even the “A phase” or “B phase”. But if you work enough with actual 3-phase power wiring, it seems odd to refer to the two conductors supplying the 240 volts as individual phases themselves simply because their source winding is one single phase. And I just never liked using “split-phase” either when looking at either of the 240 volt conductors in relation to a neutral or center-tap connection because again the phasing was created up stream. You can tap that 240 volt winding anywhere and create a myriad of different voltages but to refer to them as phases doesn’t seem to really relate to the true rotational phase of the AC voltage. And reversing wire connections in an attempt to create polarity is just simply reversing the the way in which the magnetic fields interact to boost or buck voltages reactive resistances.
Visitor from Norway. From Europe we have for a long time wondered about the strange US split phase low voltage, high current distribution system. In most of Europe we now use 230/400V 3 phase TN - network for private homes. With 3phase the motors are simpler with no capacitors that often fails after some years. With a rotating magnetic field, the rotation direction can easily be reversed too. Very practical to open garage doors.
Brilliant Dave. Absolutely the best instruction I have ever seen in any venue on any subject, and I've seen a lot. I'm going to watch every one. Much thanks, what a gift you have.
Brilliant, but WRONG Conclusion. . . He is not even looking correctly at his Own drawing. . . The Reference point is the Grounded Neutral point. . . All should be referenced to the Zero or Neutral point.
Three comments. One and foremost is this is a great presentation, well done sir. Two, electricians measure from the neutral to phase, and the first graph illustrates that best. In that graph, the two sine wave are clearly 180 degrees out of phase with respect to the neutral. Three, the opposing phase demonstration is more of a parallel circuit. Just go ahead and fold it in half, the batteries are now aligned with one another. Connect the leads that were on opposite ends. I’m claiming the batteries are in phase in phase, same current out, same in. Being in phase, the bottom light has no voltage to work and remains off. All that being said, you are really spot on by defining the reference point. As an old sparky, I’m standing by my neutral and claiming 180 degrees out of phase…
Dave, at the beginning of the video you explained if the turns were reversed at the neutral point that it would be out of phase. It would not be out of phase, but instead it would be reversed polarity. Reversing the polarity would give you two 120 circuits and a net zero for full tap. It is how a regulator works with using reverse polarity and using the same winding to be able to raise or lower the voltage, but any single winding coming off a highline single phase will always be in phase of each other.
@@I_SuperHiro_I Yeah. Reversing the polarity is essentially multiplying the sine wave by negative one, which is the same as being 180 degrees out of phase.
Your videos are wonderful. I have degrees in EE and CS but I have been a programmer in medical imaging research for most of 25+ year career (did a little engineering work in the early days). I am interested in relearning at least some of the information I have sadly forgotten over this period of time.
I'm on about the same track. EE the worked in architectural engineering for a couple years then got into comp sci (had a comp sci minor in college, and programmed during high school). I've been doing mostly line of business applications with some public facing sites. I'd like to get into something a little different though. How did you get into medical imaging?
Thank you for that explanation. It cleared up in my mind how the phases work. Why it's called single phase power but we can get 2 different phases with respect to the neutral.
I wanted to explain better my concepts to customers as English is not my native language and this video was absolutely outstanding. Beyond your evident electrical knowledge, it's your ability to explain and transmit that knowledge, plus the nice quick practical setup, your whiteboard and the camera job, it's what makes this truly remarkable and creates huge impact. I will be recommending your channel. Kudos, Dave. I am subscribing to keep learning ,refresh my knowledge and pick up your words & sentences!
I have asked many so called experts how a negative current could exist below the neutral and not shock you when touched. This has finally explained what they could not explain. Thank You Sir
Mr Gordon. You do nott know how much I have lerned from your videos. You explain so easy the things and with so easy analogies and vocabulary that is very easy to grasp. As someone said I wished I could had a teacher o a mentor like you! Keep on the outstanding content!
Beautiful explanation Dave, helped me to visualize what's happening. Your explanation about the transformer coil winding direction really helped me a lot.
@@davegordon6819 Thank you so very much for this video. It even surpasses your fantastic Open Neutral video. This video should be considered to conclusively shoot-down the "180° out of phase" belief once and for all. I reasoned this all out myself a while ago and have been trying to explain this (the two legs can't be additive if they're out of phase) to people, but this demonstrates it better than I can explain by far!
You can't choose two different reference points for two signals to determine if they are in phase or not. You need a common reference point. Why not use ground? Oscilloscopes use ground as the reference point. If you do that then you find that you will see two sine waves that are 180 degrees out of phase on the oscilloscope screen. If you want to call that "in phase" then go ahead, but it's clearly inverted.
I've been trying to make a similar argument here and the naysayers have zwro answers in return for me. If someone wants to call a straight line (0 or 180 degrees, either) in phase by virtue of there being no 'angle' that's fine, but as you say, phase relationships require common reference points. Same in geometry to draw an angle: it needs a vertice.
@@spruce_goose5169 it's like some people have already decided to call this "in phase" and they are trying to find analogies to attempt to justify their belief. They aren't really trying to address the elephant in the room which is that with ground as your reference point, the two sine waves are in fact 180 degrees out of phase. They get annoyed when anybody who went to engineering school sees the waveforms and says "those are 180 degrees out of phase" because, well, they are. Just get over it. It doesn't matter, it doesn't change anything. Electricity still works.
I appreciate your attempts, but I don't see *_ANY_* of your other comments. It is somewhat of a "slight of hand" trick to move the reference between measurements. If you're allowed to do that, I can show you how the primary winding is out of phase with itself.
@@MartinVandepas when generators operate its my understanding that phase one starts at the north pole of a magnet while phase two starts at the south pole of the magnet which would always keep them 180 degrees apart from each other. having a tough time taking this guy seriously.
They are out of phase only on the osciloscope screen. In reality they are in phase and are ADDING UP!!!! If they were truly out of phase 180 degrees then the voltage between the two legs would be ZERO!!!!
Came from another video that suggested that they were not in phase. This video did an outstanding job of explaining how to think about this, specficially using the reference points. Thank you so much for this!
Your explanation is simply superb. I've seen and heard many discussions on this but not with this level clarity and demonstrations to illustrate the concept.
Kids, if you try this at home make sure you have your scope powered thru an isolation transformer, unless of the portable battery operated type which are much more common these days, excellent presentation by the way
+1 This experiment generally won't work with oscilloscopes that plug into the wall because they're referenced to earth. The little (negative) clip on the probe is shorted to the ground pin of the plug. Earth is bonded to neutral at the panel, so if you put the clip on live, you'll complete the circuit and make a lot of smoke, sparks, and fire.
This is an excellent representation of phase angles and "polarity" in a split-phase system! I've been an electrician and electro-mechanical systems tech for over 40 years. And while I understand the principles described here, it's often hard to convey it to someone not in the field. But you have demonstrated it beautifully here! Thanks for sharing your knowledge.
It mentions nothing about why they are out of phase, it mentions nothing about positive sequence, negative sequence, or zero sequence. This is a very very very watered down version of what phase angles really are, how they’re used to analyze a circuit, and how they effect our power systems.
@@Electric_Sherlock Well then, please... enlighten us all by posting your own video describing it! Actually, he never gets into "phase angles" at all (as would be the case in 3-phase systems). Nonetheless, a great representation of split-phase systems. If you can explain ot better, please do.
@@Calico5string1962sure. Here you go. 120/240 refers to a type of electrical power system. In-phase means the two 120V lines are synchronized in their waveforms, providing 240V when combined. Out-of-phase indicates the waveforms are not synchronized, disrupting the combined voltage. Simple. See how i took a loooooooong video and made it simple in a mere 2 sentences. Dont unleash my sarcasm and brilliance, you’ll regret it. Despite your “40years” of so-called experience. Experience doesn’t equal knowledge anymore than standing in a garage make you a car.
Thank you for this. I've been watching too many TH-cam videos where electricians understand the system only in metaphorical terms. This was really helpful to properly understand the flow of electrons in the single phase system.
His drawing and explanation correctly shows the electron flow, but he failed to refer everything to the correct Reference point, which is the Neutral point. . . . That is what Neutral means.. . . Same with 3-phase, all 3 live lines have AC voltage relative to the Neutral point.
@@stevenj100 Current flows from voltage to no voltage. . . . So each of the 120V lines current does effectively flow to the Neutral.. .. But because the TWO Live lines are running in opposite directions, that is 180° then the TWO Live current Cancel each other out in the Neutral, so the Neutral only carries the Difference current, and not the combined Total current.
@@stevenj100 AC is Alternating Current, So In or Out does not really mean anything, because they are alternating, that is why it is important to understand the correct AC Phase relationship of TWO Live 120V Lines.. . . If there is 5 Amp in one Live line and 8 Amps in the other Live line, then the Neutral Current would be 3 Amps, on 2-phase 180° systems, and more complicated on 120° 2-phase, and 3-phase systems.
I really hate the phrase "cancel each other out". That's how you might do the math, but it isn't what is happening relative to current. Any load that can travel from one hot leg to the other will, because it is a preferred path. Any imbalanced load will travel on the neutral.
@@jasonbeisiegel5550 Actually cancel each other out is a very important thing to understand. . . . This enables us in big systems, to use smaller Neutral wires. . . You also need to understand then when there are neutral wire connection problems.
Worth noting that a scope plugged into a wall will see out of phase because the "negative" lead is actually connected directly to the earth/group pin going into the wall. That's a warning for anyone who might want to scope their AC. Don't connect the little alligator clip to live. You're going to have a bad time. Ultimately earth is the base reference that people are using when discussing the phase of the two secondary coils (or two sides of the secondary coil). When you use that reference, they're out of phase. If you reference one end of the transformer for one measurement and then *_move that reference_* to the center for the other measurement, they're in phase. Actually, if you move your reference, you can make them in phase or out of phase as you please.
That's a good disclaimer. Best case scenario, your scope will meet an untimely end. Best to find a decent quality CAT rated differential probe for such measurements.
You can't actually make them in or out of phase arbitrarily, though you can create the illusion by incorrectly handling and discarding of art of the information. There was also major mistake in the video. Basically he conflated true signed potentials with useful absolute potentials. in otherwords -3v can do the same work as +3v but they are not the same when it comes to measuring and graphing phase separation.
Perfect explanation and demonstration, thank you Dave! I have tried to explain what single phase means and that split phase is like a center tap transformer used in electronic power supplies. Most people just po-po me saying "it has always been 180 degrees out of phase" and they won't change their thinking.
I assumed that it was 180 degree out of face, but when tried to analize vs the center tap.. I got a short circuit in my head.... but never had the opportunity to see it through an Oscilloscope to reveal how current flows between phases and the neutral at the same time..... wonderful explanation... greatly appreciated!!
I teach automotive basic electrical, so while i come as a learner I also watch with my teacher hat on. You have a great style of delivery! Nicely done explanations. Also, since i'm used to working with some pretty large DC circuits (starters, alternators, and my house also has large 12 and 48v inverter circuits) I experienced an subconscious discomfort at how hard you were working those D cells. Lol
Thank you, I am a curious, jack of all trades, master of none type of person who has always just accepted the split phase / out of phase concept without fully understanding. I understand it now. Once again, thank you.
Thanks Dave. I'm in my mid 60s, have a physics background (I understand electricity from Maxwell to Feynman), over-the-top experience in res. wiring and, until now, have never fully understood "split phase"! THANKYOU.
*THANK YOU* for this! I have been trying to explain this to people for a while, and this demonstration perfectly outlines everything I've envisioned and understood. The principle of number of turns is key, as that not only directly relates to voltage (transformer ratio), it also means that if "180° out of phase" were true, then 240V could never be made. Again, thank you for this fantastic complete demonstration and explanation!
Let me try to come to your page since our previous attempt went nowhere. You make the claim several times in these comments that it is utter folly to use the center tap (neutral) as a constant reference. I have one simple question I am hoping you will humor me by answering: Why is it folly to do as such in a split phase scenario, yet it is common-- standard in fact-- to use a common reference when determining phase angles in 3 phase? If you disagree that it is the standard to measure 3 phase relationships off a common neutral, please work with me on that. That would be our sticking point. If you agree with that but think there is some fundamental difference in the way split and 3 phase are measured, help me understand what that fundamental difference is.
I got a summer job with a company named "Eastern Electric". They were a transformer winding shop that specialized in large transformers and were partly owned by Westinghouse. Most smaller winding shops want nothing to do with audio transformers. Other specialize in audio & consumer electronics, tool & appliance transformers too but won't touch medical device transformers with a 10 foot pole. Basler does it all from gigantic oil filled substations to teeny tiny dry signal transformers. I have to say Westinghouse made some enormously gigantic transformers that even dwarfed Basler's way huge transformers. These super mega-huge transformers took special rail cars to ship them out to mines & power plants.
Got to say I've watched so many videos, and this is the ONLY explanation that I've been able to understand 220V in phase. Nice job, you should be at MIT
This was a great video. Even having taken circuits courses in college, my understanding wasn't that great. Your demonstration was concise and easy to follow.
Brilliant and I concur. In your demonstration you could have gone further by fliping both side of the battery bank to simulate alternating current. Doing so would also explain the fundamental difference between hot and neutral when connecting across half the length of the coil to obtain 120V. There would be no current at the neutral when the load is the same on both halves of the coil. When the load is imbalanced there is a net current flowing through the neutral. When there is a complete imbalancd i.e. no load on one side of the coil the current flowing at the neutral is the same as that of the current flowing through the hot. Also add the resulting graphs of the superimposed sine waves. The two out of phase would be a flat line, the two in phase would a sine wave with greater amplitude. In practice there is not a problem of overloading the neutral as these lines are joined at the thick bus bar in the electrical panel.
Thank you cannot tell you how many times I've had this conversation and was unable convince people that L1 and L2 are in phase. I'll use your explanation for now on.
If you leave your reference at ground/earth, they're out of phase. If you move your reference like Dave did, you can make them in phase or out of phase as you please.
Fabulous Sir! You explained this and the phase relationship in a much shorter time frame than any of my proffesors did. Short story...When I was a young guy and just graduated College with a Degree in Electronics Engineering I was talking with an older one of my bosses about house wiring and single phase... 3 phase stuff etc. He told me whenever he needed 220v he just connected both 110v house wires ....TOGETHER! 110+110=220 right? I just froze and looked at him and was like..."Ummm yeah, you can't do that"
My goodness, unlike most yt authors, your audio has got to be the BEST out there. It's loud enough, not muffled. I have told friends "never use a laptop microphone to make videos" - few listen. I wonder if your mic is a lapel type with a cable connection to the video camera? Regardless, for those with interest in this subject, you'd done a huge favor, thank you!
Amazing tutorial.This just clarified all of my confusion about how 120/240 single-phase and 240 3-phase can all operate on 3-phase 4-wire systems. Your ability to communicate this is amazing!!!
Thank you for correctly explaining this. So many people incorrectly think this is out of phase because they can generate the first sign wave form on an o’scope. Unfortunately, I’ve seen some explanations take the first sign wave form and say the voltage can be measured between the peaks. This is fundamentally incorrect, because if measured using the same reference, this would, as you demonstrated with the DC circuit, result on zero volts.
Two out of phase signals will cancel if you add them. If you measure the *_difference_* between them, you're actually subtracting them. If you connect a load, the current across the load is given by the *_difference_* between the voltage on either side of the load. I = (V1 - V2)/R The issue with the video is that Dave moves his reference.
This is a world-class presentation! People get killed because they don't see that individual 120 V branches have the same load on their own neutrals as the "hot" when running even though collectively, the neutral only carries unbalanced loads. The two sides of a single-phase panel are legs, not phases, and the use of the term should be "phased out." LOL.
Appreciate it. People say quite readily that the two sides are 180° "out of phase". Then, to make matters worse, they tell you to *subtract* the instantaneous voltages to get the total. To me, "out of phase" means adding them gives you 0. Like the Theory of Relativity, it really depends from where you are looking at it.
With earth/ground as a reference, the two sides of a split phase system *_DO_* add to zero. One is positive while the other is negative. When you connect a load across those phases, what matters is the *_difference_* between the two voltages... not adding them together. Remember how you calculate current through a resistance. I = (V1 - V2)/R where V1 is the voltage on one side of the resistance, and V2 is the voltage on the other side. For example, if V1 = V2, there will be zero voltage *_across_* the resistance, and therefor no current will flow.
I always looked at it intuitively from the center point as the reference, where the difference between the two waves accounts for the greater amplitude. There is more area between the lines. A three phase system is truly out of phase, and from the difference between them at any point of time we can extract current. But of course one full winding has to be continuous.
Thank you for this videos! I appreciate all of your material! You have a great gift of putting the subject into terms that can be understood. I look forward to more videos in the future.
Wow! GREAT JOB! I have finally found someone that shows exactly what I have been saying for many years. When you try to explain this in a comment it is hard to get the point across! I have been saying that since oscilloscope is connected to neutral as common, it only looks like half is out of phase. You explained it perfectly. In phase to me is a point in time! And when someone says it is out of phase, it drives me nuts. I will be sharing this video with others.
Thanks for explaining this. I have the delta 3 phase and did not understand how it worked. I use all of it on a 5hp pump but split off 2-120's for shop equipment.
Very nice description. Many others have mentioned your unusual US split phase system but not explained how it works. Thanks. It was interesting to see in your practical demo the phase to phase light still lit even though you had removed the batteries to reverse them. The phase to neutral lights had extinguished but phase to phase still lit. A nice demonstration of leakage current that you might want to demonstrate some time.
As always in these 'paradoxes', it's the assumption(s) that are in conflict. In particular, for a voltage measurement, you have to define the relevant reference point for each measurement. In this case we (I/you/they) can have two different views of which end of 'the other coil' is to be a reference. If we go with the centre tap as a common reference, the voltages are out of phase (opposite), while if we measure based on the diagram with 'top' end as the measurement, and the 'bottom' end as reference (which moves physically depending on coil), then we get the in-phase answer (for the Voltage!). Check for the direction of current flow - in some arrangements (3 coils in sequence) you can get the current to flow the 'wrong way' (two + and one -, makes for a single + voltage to the load). Great explanation by Dave.! And remember it for any of the other paradoxes you bump into, all based on mistaken assumptions ;-)
pretty much all you said is correct. You glossed over the fact that your clamp ammeter in DC would have given opposite signs if turned the other way around but that did not matter much for the point. Altogether, very clear if not exactly surprising for folks familiar with meters and scopes. Thank you. However, for safety reasons, I feel that you should have made a strong point at the end when discussing results from the ground lead of the scope to L2, that this should NOT be done in real life. It WILL BLOW UP your lead and/or scope because that would essentially be a dead short between L2 at 120V and mains ground through the scope's ground lead. As it stands, a curious person not familiar with scopes may just try that to verify your (correct) assertions and be in for a bad and dangerous surprise.
Not phases. We usually call them _legs_ because they are not different phases, and the legs are a metaphor for the entire secondary winding of the transformer.
Thank you so much for making this video! No other video I found explained the reference for the two sine waves before, and you really helped me have a lightbulb moment.
I believe my plain concept on current leading the voltage on distribution lines vs the voltage leads the current after the circuit breaker box in our homes is very great . Relating that to a city of service panels at different current (amperage) ratings we can see how much a town is using in current. And also how many circuit breakers we use in a breaker panel , 200 amp service can handle a quantity of 10 20 amp breakers at 120 / 240 volts each!
I very much enjoyed this video and its explanation of the output of a center tapped transformer. I particularly liked the example of flattening one sine wave to demonstrate a single phase of twice the amplitude. I understand that the output differs from say a three phase generator where the coils and rotation cause the phases to be physically sepearated by 120 degrees along the time axis, but I find arguing about the "in phase" of "out of phase" argument about household current about as useful as agruing whether a Zebra is white with black stripes or the reverse. Once you understand how it works and what is happening I think the distinction is meaningless. The output of the center tapped transformer when referenced to neutral behaves exactly as two seperate mechanically produced phases would. I have always thought as the wave as "flipped" as opposed to shifted 180 degrees. I would like to see an experiment where someone built a two phase generator running 180 degrees out of phase rather than the conventional 90 deg and hooked that output to three test points and then hooked the output of a center tapped to three others. With the sources of the power hidden. I wonder if it would be possible to identify which was which. Thanks for a great video. I always find that thinking of things like this in as many ways, with as many examples as possible really helps to visualize what's actually going on.
Damn it. 20 years in the trade and this was always something I wondered about and you explained it in just a few minutes. Excellent video. I look forward to more!
The split phase setup is always single phase and neutral and live conductors have the same cross section. Early true two-phase systems were 90º out of phase and if a neutral conductor (usually called ground back then) was used it had to have twice the cross section of the live conductors, otherwise otherwise two conductors were used for each phase. That system allowed to make simple AC motors that would start without the help of external devices like capacitors, it also allowed to easily change the direction of rotation of the motors.
Great video and I agree with everything you said except the terminology. L1 will always be 180° out of phase when compare to L2 and vice versa. If L1 is at +120 then L2 is -120. The in phase, out of phase terminology is really just a comparison to 3 phase to depict that L1 and L2 are always in sync with each other where in 3 phase power L1, L2 and and L3 are 120° apart
I agree with you. L1 and L2 have to be out of phase with one another would respect to their sine waves otherwise how would you measure any voltage between them.
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At 74 years old and been working in an electrical environment for more than 50 years I have never seen a good explanation like this. Would have loved to have you as my tutor. Keep the videos coming.
Choose better environment 😅
@@K1-1can’t just move where you want with liberals scalping and raising the costs of living in all electrical concentrated areas
@@K1-1 rude
This has never made complete sense to me until now. 9 years in the trade and 5 licensed and now I get it. Thank you!
the biggest issue is arrogant electricians.. the teachers (typically former electricians int he field) will want to "skip" over stuff, to appear to be "macho" to the guys from the union or for those working in industrial. He will say stuff like "I know you guys know this stuff so we can run through this part, but if you dont raise your hand". therefore making it a matter of ONE guy looking "less of a man" for raising his hand. AND DONT LET that man be a minority among a bunch of white men.. because then theres a DOUBLE whammy feeling. the white guys looking upon you as if youre stupid.
this is why teachers need to be TEACHERS ... like this man is doing.
This is kind of people/profesor we need to have in schools. Amazin
A most unusual video where the explanation was unique and a credit to the Dave Gordon.
I have never seen the concept of vectors addressed to the non maths audience in this fashion with attention to detail . You sir are a credit to your profession.
But wrong conclusion.. . He failed to identify the correct Reference point, which is and has to be the Zero or Neutral point. . . . Looks as if he sort of used the paper as his reference. . . . Paper does not carry electrical current, wires do, so you have to use the correct electrical point, which is the Zero or Neutral point.
This man makes these concepts very understandable. Visual learning is a must for many. Great iob sir.
Please make more videos. By far these have been the most helpful I have come across. Easy to follow and clearly explained. Truly a great instructor.
Unfortunately Wrong. . . He failed to use the correct Reference point, which is simply the Zero or Neutral point.
Glad to see that you're still posting videos. Still my favorite teacher regardless I won't be able to have you as a teacher anymore :)
Thanks for your support Devan. I hope they're still giving you good opportunities to work with a variety of equipment out in the field.
Agree!!! Keep us teaching please!
Apologies if this adds some confusion but just trying to add some clarity. Let’s start with the basic single winding you are showing as the voltage source and let’s look at it without any mid-tap, center-tap, neutral, or split-phase tap connection. i.e. Just the winding. In reality this is a winding as part of a transformer, possibly your home or business pole or pad mounted transformer. If we can agree that this winding is receiving its energy as a secondary winding to a primary winding, which is being fed from a generation source, then it would seem that our interest in labeling any of the downstream, secondary wiring as “in-phase” or “out-of-phase” should always be in reference to any of the other transformer primary windings. With this approach, I am looking at our common electrical power generation and distribution system, where for example, the hydro-electric plant’s generator creates voltages via 3 distinct windings and because the armature is rotating across these 3 windings at different times, we have 3 windings which are physically arranged to be producing voltages 120 degrees (1/3 of 360) from each other. These three windings are then tied together in series, or some would say in a delta connection with three tap conductors to be extended out through various control and distribution apparatus to our local pad or pole mounted transformers. And back to my point, it is these conductors that will impact on our reference to phasing, or as we commonly label - A Phase, B-Phase, and C-Phase. My own education has me of the understanding that our commonly used system of 120/240 volts is simply a secondary winding of a local utility power transformer, which is being induced with a 240 volt voltage from a primary winding being fed from 1 or 2 of these original hydro-electric source conductors. And I include the possibility of 1 source conductor simply because in some cases the primary voltage to our local transformers may just be a primary winding utilizing one source conductor and a common grounding tie with the secondary. So when I look at this discussion, I tend to disregard references to phasing within any of the secondary 120/240 volt wiring because to me the phase of this wiring is linked to whatever source conductor or conductors are used to power the local primary winding. Yes, you could have true original source phasing within the home or business system, but it would be because the 3-phase power has been brought in and is fully utilized to power a 3-phase transformer which in turn has 3-phase secondary windings, possibly delta or Y connections. Having offered this, I also acknowledge the ability to engineer electrical phasing to operate certain 3-phase equipment. But when I read the original question Dave put out there, relative to the AC sine-wave(s), I just immediately assume it is in phase due to how the 240 volt secondary winding is powered. And I am still open to being re-educated as to how to look at phasing. I do also understand that when we want to refer to either side of the 240 volt power source, we tend to say the “black phase” or the “red phase” or even the “A phase” or “B phase”. But if you work enough with actual 3-phase power wiring, it seems odd to refer to the two conductors supplying the 240 volts as individual phases themselves simply because their source winding is one single phase. And I just never liked using “split-phase” either when looking at either of the 240 volt conductors in relation to a neutral or center-tap connection because again the phasing was created up stream. You can tap that 240 volt winding anywhere and create a myriad of different voltages but to refer to them as phases doesn’t seem to really relate to the true rotational phase of the AC voltage. And reversing wire connections in an attempt to create polarity is just simply reversing the the way in which the magnetic fields interact to boost or buck voltages reactive resistances.
Beautifully said.
Visitor from Norway. From Europe we have for a long time wondered about the strange US split phase low voltage, high current distribution system. In most of Europe we now use 230/400V 3 phase TN - network for private homes. With 3phase the motors are simpler with no capacitors that often fails after some years. With a rotating magnetic field, the rotation direction can easily be reversed too. Very practical to open garage doors.
Nice job Dave. I am proud to have you in the IBEW
Brilliant Dave. Absolutely the best instruction I have ever seen in any venue on any subject, and I've seen a lot. I'm going to watch every one. Much thanks, what a gift you have.
Brilliant, but WRONG Conclusion. . . He is not even looking correctly at his Own drawing. . . The Reference point is the Grounded Neutral point. . . All should be referenced to the Zero or Neutral point.
Three comments.
One and foremost is this is a great presentation, well done sir.
Two, electricians measure from the neutral to phase, and the first graph illustrates that best. In that graph, the two sine wave are clearly 180 degrees out of phase with respect to the neutral.
Three, the opposing phase demonstration is more of a parallel circuit. Just go ahead and fold it in half, the batteries are now aligned with one another. Connect the leads that were on opposite ends. I’m claiming the batteries are in phase in phase, same current out, same in. Being in phase, the bottom light has no voltage to work and remains off.
All that being said, you are really spot on by defining the reference point. As an old sparky, I’m standing by my neutral and claiming 180 degrees out of phase…
Mr. Dave, you are the Biggie Smalls of the electrical world. Your elegance with words and understanding of the hood is amazing!
OMG. Thank you! I have worked in an electrical environment for 25 years and have never come across such a clear explanation.
Dave, at the beginning of the video you explained if the turns were reversed at the neutral point that it would be out of phase. It would not be out of phase, but instead it would be reversed polarity. Reversing the polarity would give you two 120 circuits and a net zero for full tap. It is how a regulator works with using reverse polarity and using the same winding to be able to raise or lower the voltage, but any single winding coming off a highline single phase will always be in phase of each other.
Practically in an AC Sine Wave, don’t they have the same effect?
@@I_SuperHiro_I Yeah. Reversing the polarity is essentially multiplying the sine wave by negative one, which is the same as being 180 degrees out of phase.
@@namejeff1050 thanks
Your videos are wonderful. I have degrees in EE and CS but I have been a programmer in medical imaging research for most of 25+ year career (did a little engineering work in the early days). I am interested in relearning at least some of the information I have sadly forgotten over this period of time.
I'm on about the same track. EE the worked in architectural engineering for a couple years then got into comp sci (had a comp sci minor in college, and programmed during high school). I've been doing mostly line of business applications with some public facing sites. I'd like to get into something a little different though. How did you get into medical imaging?
Perfect
I'm an hvac technician and find these videos extremely useful
Brilliant! Been searching for this exact explanation for years🎉
Thank you for that explanation. It cleared up in my mind how the phases work. Why it's called single phase power but we can get 2 different phases with respect to the neutral.
I wanted to explain better my concepts to customers as English is not my native language and this video was absolutely outstanding. Beyond your evident electrical knowledge, it's your ability to explain and transmit that knowledge, plus the nice quick practical setup, your whiteboard and the camera job, it's what makes this truly remarkable and creates huge impact. I will be recommending your channel. Kudos, Dave. I am subscribing to keep learning ,refresh my knowledge and pick up your words & sentences!
Brilliant, guys like Dave are the type people that I study to level up.
I have asked many so called experts how a negative current could exist below the neutral and not shock you when touched. This has finally explained what they could not explain.
Thank You Sir
Mr Gordon.
You do nott know how much I have lerned from your videos. You explain so easy the things and with so easy analogies and vocabulary that is very easy to grasp.
As someone said I wished I could had a teacher o a mentor like you!
Keep on the outstanding content!
Beautiful explanation Dave, helped me to visualize what's happening. Your explanation about the transformer coil winding direction really helped me a lot.
The lightbulb setup really helps it click for me. Thanks for the education.
You're very welcome Joe. I'm glad the lights light it up for you :)
@@davegordon6819 Thank you so very much for this video. It even surpasses your fantastic Open Neutral video. This video should be considered to conclusively shoot-down the "180° out of phase" belief once and for all. I reasoned this all out myself a while ago and have been trying to explain this (the two legs can't be additive if they're out of phase) to people, but this demonstrates it better than I can explain by far!
You can't choose two different reference points for two signals to determine if they are in phase or not. You need a common reference point. Why not use ground? Oscilloscopes use ground as the reference point. If you do that then you find that you will see two sine waves that are 180 degrees out of phase on the oscilloscope screen. If you want to call that "in phase" then go ahead, but it's clearly inverted.
I've been trying to make a similar argument here and the naysayers have zwro answers in return for me.
If someone wants to call a straight line (0 or 180 degrees, either) in phase by virtue of there being no 'angle' that's fine, but as you say, phase relationships require common reference points. Same in geometry to draw an angle: it needs a vertice.
@@spruce_goose5169 it's like some people have already decided to call this "in phase" and they are trying to find analogies to attempt to justify their belief. They aren't really trying to address the elephant in the room which is that with ground as your reference point, the two sine waves are in fact 180 degrees out of phase. They get annoyed when anybody who went to engineering school sees the waveforms and says "those are 180 degrees out of phase" because, well, they are. Just get over it. It doesn't matter, it doesn't change anything. Electricity still works.
I appreciate your attempts, but I don't see *_ANY_* of your other comments.
It is somewhat of a "slight of hand" trick to move the reference between measurements. If you're allowed to do that, I can show you how the primary winding is out of phase with itself.
@@MartinVandepas when generators operate its my understanding that phase one starts at the north pole of a magnet while phase two starts at the south pole of the magnet which would always keep them 180 degrees apart from each other. having a tough time taking this guy seriously.
They are out of phase only on the osciloscope screen. In reality they are in phase and are ADDING UP!!!! If they were truly out of phase 180 degrees then the voltage between the two legs would be ZERO!!!!
Came from another video that suggested that they were not in phase. This video did an outstanding job of explaining how to think about this, specficially using the reference points. Thank you so much for this!
Thank you Dave I really appreciated you describe this in phase and out of phase it was excellent
What a clear, concise explanation. Thanks
Dave you are an excellent teacher Keep the good work up.
Your explanation is simply superb. I've seen and heard many discussions on this but not with this level clarity and demonstrations to illustrate the concept.
Kids, if you try this at home make sure you have your scope powered thru an isolation transformer, unless of the portable battery operated type which are much more common these days, excellent presentation by the way
+1 This experiment generally won't work with oscilloscopes that plug into the wall because they're referenced to earth. The little (negative) clip on the probe is shorted to the ground pin of the plug.
Earth is bonded to neutral at the panel, so if you put the clip on live, you'll complete the circuit and make a lot of smoke, sparks, and fire.
This is the most helpful explanation that I have heard on 120/240 phasing...looking at dc voltage was the key to me.
This is an excellent representation of phase angles and "polarity" in a split-phase system!
I've been an electrician and electro-mechanical systems tech for over 40 years. And while I understand the principles described here, it's often hard to convey it to someone not in the field. But you have demonstrated it beautifully here!
Thanks for sharing your knowledge.
It mentions nothing about why they are out of phase, it mentions nothing about positive sequence, negative sequence, or zero sequence. This is a very very very watered down version of what phase angles really are, how they’re used to analyze a circuit, and how they effect our power systems.
@@Electric_Sherlock
Well then, please... enlighten us all by posting your own video describing it!
Actually, he never gets into "phase angles" at all (as would be the case in 3-phase systems). Nonetheless, a great representation of split-phase systems.
If you can explain ot better, please do.
@@Calico5string1962sure. Here you go. 120/240 refers to a type of electrical power system. In-phase means the two 120V lines are synchronized in their waveforms, providing 240V when combined. Out-of-phase indicates the waveforms are not synchronized, disrupting the combined voltage. Simple. See how i took a loooooooong video and made it simple in a mere 2 sentences. Dont unleash my sarcasm and brilliance, you’ll regret it. Despite your “40years” of so-called experience. Experience doesn’t equal knowledge anymore than standing in a garage make you a car.
Thank you for this. I've been watching too many TH-cam videos where electricians understand the system only in metaphorical terms. This was really helpful to properly understand the flow of electrons in the single phase system.
His drawing and explanation correctly shows the electron flow, but he failed to refer everything to the correct Reference point, which is the Neutral point. . . . That is what Neutral means.. . . Same with 3-phase, all 3 live lines have AC voltage relative to the Neutral point.
@@stevenj100 Current flows from voltage to no voltage. . . . So each of the 120V lines current does effectively flow to the Neutral.. .. But because the TWO Live lines are running in opposite directions, that is 180° then the TWO Live current Cancel each other out in the Neutral, so the Neutral only carries the Difference current, and not the combined Total current.
@@stevenj100 AC is Alternating Current, So In or Out does not really mean anything, because they are alternating, that is why it is important to understand the correct AC Phase relationship of TWO Live 120V Lines.. . . If there is 5 Amp in one Live line and 8 Amps in the other Live line, then the Neutral Current would be 3 Amps, on 2-phase 180° systems, and more complicated on 120° 2-phase, and 3-phase systems.
I really hate the phrase "cancel each other out". That's how you might do the math, but it isn't what is happening relative to current. Any load that can travel from one hot leg to the other will, because it is a preferred path. Any imbalanced load will travel on the neutral.
@@jasonbeisiegel5550 Actually cancel each other out is a very important thing to understand. . . . This enables us in big systems, to use smaller Neutral wires. . . You also need to understand then when there are neutral wire connection problems.
Very nice and generous teacher!!
Best teacher ever. Please post more videos. Thanks
I am from Africa, I enjoy electricity and electronics .
Whaooo. The best video lecture, I've ever seen, on a transformer explained and illustrated in detail. Please, keep it up.
I really enjoy a lecture using electron flow. When studying CRT tubes, it is the electron beam moving. Great presentation. Thank you.
WOW! I have never thought of using DC as demonstration of AC. Brilliant!
Worth noting that a scope plugged into a wall will see out of phase because the "negative" lead is actually connected directly to the earth/group pin going into the wall.
That's a warning for anyone who might want to scope their AC. Don't connect the little alligator clip to live. You're going to have a bad time.
Ultimately earth is the base reference that people are using when discussing the phase of the two secondary coils (or two sides of the secondary coil). When you use that reference, they're out of phase. If you reference one end of the transformer for one measurement and then *_move that reference_* to the center for the other measurement, they're in phase. Actually, if you move your reference, you can make them in phase or out of phase as you please.
That's a good disclaimer. Best case scenario, your scope will meet an untimely end.
Best to find a decent quality CAT rated differential probe for such measurements.
No point in doing that when a 24Vac center-tap transformer will display the same results only its safely scaled down to non-lethal voltages 😊
You can't actually make them in or out of phase arbitrarily, though you can create the illusion by incorrectly handling and discarding of art of the information. There was also major mistake in the video. Basically he conflated true signed potentials with useful absolute potentials. in otherwords -3v can do the same work as +3v but they are not the same when it comes to measuring and graphing phase separation.
Perfect explanation and demonstration, thank you Dave! I have tried to explain what single phase means and that split phase is like a center tap transformer used in electronic power supplies. Most people just po-po me saying "it has always been 180 degrees out of phase" and they won't change their thinking.
I assumed that it was 180 degree out of face, but when tried to analize vs the center tap.. I got a short circuit in my head.... but never had the opportunity to see it through an Oscilloscope to reveal how current flows between phases and the neutral at the same time..... wonderful explanation... greatly appreciated!!
I teach automotive basic electrical, so while i come as a learner I also watch with my teacher hat on. You have a great style of delivery! Nicely done explanations. Also, since i'm used to working with some pretty large DC circuits (starters, alternators, and my house also has large 12 and 48v inverter circuits) I experienced an subconscious discomfort at how hard you were working those D cells. Lol
Thank you, I am a curious, jack of all trades, master of none type of person who has always just accepted the split phase / out of phase concept without fully understanding. I understand it now. Once again, thank you.
Thanks Dave. I'm in my mid 60s, have a physics background (I understand electricity from Maxwell to Feynman), over-the-top experience in res. wiring and, until now, have never fully understood "split phase"! THANKYOU.
Thank you for this clear explanation of in-phase and out-of-phase.
Very fantastic Explaination😊
This is a much better explanation of this concept than any of the other videos I've found today, most of which were scattered and incoherent.
*THANK YOU* for this! I have been trying to explain this to people for a while, and this demonstration perfectly outlines everything I've envisioned and understood. The principle of number of turns is key, as that not only directly relates to voltage (transformer ratio), it also means that if "180° out of phase" were true, then 240V could never be made. Again, thank you for this fantastic complete demonstration and explanation!
Let me try to come to your page since our previous attempt went nowhere.
You make the claim several times in these comments that it is utter folly to use the center tap (neutral) as a constant reference. I have one simple question I am hoping you will humor me by answering:
Why is it folly to do as such in a split phase scenario, yet it is common-- standard in fact-- to use a common reference when determining phase angles in 3 phase?
If you disagree that it is the standard to measure 3 phase relationships off a common neutral, please work with me on that. That would be our sticking point. If you agree with that but think there is some fundamental difference in the way split and 3 phase are measured, help me understand what that fundamental difference is.
Geez. Me thinks Jovet swam too deep. Confidence > comprehension perhaps. Came out swinging he did.
Wonderful video. clear concise. Secondary inductor turned THE SAME WAY all the way thru. thank you
always wondered about that.
I got a summer job with a company named "Eastern Electric". They were a transformer winding shop that specialized in large transformers and were partly owned by Westinghouse. Most smaller winding shops want nothing to do with audio transformers. Other specialize in audio & consumer electronics, tool & appliance transformers too but won't touch medical device transformers with a 10 foot pole. Basler does it all from gigantic oil filled substations to teeny tiny dry signal transformers. I have to say Westinghouse made some enormously gigantic transformers that even dwarfed Basler's way huge transformers. These super mega-huge transformers took special rail cars to ship them out to mines & power plants.
Superb AC current flow using DC batteries. You are a master indeed.
Great video. Best explanation I’ve seen
Such an elegant explanation. Kudos from an EE.
Got to say I've watched so many videos, and this is the ONLY explanation that I've been able to understand 220V in phase. Nice job, you should be at MIT
This was a great video. Even having taken circuits courses in college, my understanding wasn't that great. Your demonstration was concise and easy to follow.
Thanks, you are a master of basic concepts of Electrical Engineering
Brilliant and I concur. In your demonstration you could have gone further by fliping both side of the battery bank to simulate alternating current. Doing so would also explain the fundamental difference between hot and neutral when connecting across half the length of the coil to obtain 120V. There would be no current at the neutral when the load is the same on both halves of the coil. When the load is imbalanced there is a net current flowing through the neutral. When there is a complete imbalancd i.e. no load on one side of the coil the current flowing at the neutral is the same as that of the current flowing through the hot. Also add the resulting graphs of the superimposed sine waves. The two out of phase would be a flat line, the two in phase would a sine wave with greater amplitude. In practice there is not a problem of overloading the neutral as these lines are joined at the thick bus bar in the electrical panel.
Videos like this are what the trades need.
Excellent explanation
Thank you cannot tell you how many times I've had this conversation and was unable convince people that L1 and L2 are in phase. I'll use your explanation for now on.
If you leave your reference at ground/earth, they're out of phase.
If you move your reference like Dave did, you can make them in phase or out of phase as you please.
Fabulous Sir! You explained this and the phase relationship in a much shorter time frame than any of my proffesors did.
Short story...When I was a young guy and just graduated College with a Degree in Electronics Engineering I was talking with an older one of my bosses about house wiring and single phase... 3 phase stuff etc.
He told me whenever he needed 220v he just connected both 110v house wires ....TOGETHER! 110+110=220 right?
I just froze and looked at him and was like..."Ummm yeah, you can't do that"
This video is amazing. You are really good at explaining conceptual things. What a fascinating and informative time
such an excellent explanation, well done
My goodness, unlike most yt authors, your audio has got to be the BEST out there. It's loud enough, not muffled.
I have told friends "never use a laptop microphone to make videos" - few listen.
I wonder if your mic is a lapel type with a cable connection to the video camera?
Regardless, for those with interest in this subject, you'd done a huge favor, thank you!
Amazing tutorial.This just clarified all of my confusion about how 120/240 single-phase and 240 3-phase can all operate on 3-phase 4-wire systems. Your ability to communicate this is amazing!!!
ALL of your confusion?
Yes, this is just one of the three phases. It doesn't matter which one. That's why this is 1PH service.
Thank you for correctly explaining this. So many people incorrectly think this is out of phase because they can generate the first sign wave form on an o’scope. Unfortunately, I’ve seen some explanations take the first sign wave form and say the voltage can be measured between the peaks. This is fundamentally incorrect, because if measured using the same reference, this would, as you demonstrated with the DC circuit, result on zero volts.
Yes! And yet people still refuse to believe it, even in these comments...
120-(-120) doesn't equal 240? News to me.
Two out of phase signals will cancel if you add them. If you measure the *_difference_* between them, you're actually subtracting them.
If you connect a load, the current across the load is given by the *_difference_* between the voltage on either side of the load. I = (V1 - V2)/R
The issue with the video is that Dave moves his reference.
This is a world-class presentation! People get killed because they don't see that individual 120 V branches have the same load on their own neutrals as the "hot" when running even though collectively, the neutral only carries unbalanced loads. The two sides of a single-phase panel are legs, not phases, and the use of the term should be "phased out." LOL.
I just discovered your videos.
By far, you are the best one for explaining .
Keep up the good work. And Thank you!
What an explanation (one of the best videos I've ever seen here) ! Thumbs up!
Appreciate it. People say quite readily that the two sides are 180° "out of phase". Then, to make matters worse, they tell you to *subtract* the instantaneous voltages to get the total. To me, "out of phase" means adding them gives you 0. Like the Theory of Relativity, it really depends from where you are looking at it.
With earth/ground as a reference, the two sides of a split phase system *_DO_* add to zero. One is positive while the other is negative.
When you connect a load across those phases, what matters is the *_difference_* between the two voltages... not adding them together. Remember how you calculate current through a resistance. I = (V1 - V2)/R where V1 is the voltage on one side of the resistance, and V2 is the voltage on the other side.
For example, if V1 = V2, there will be zero voltage *_across_* the resistance, and therefor no current will flow.
@@Falcrist Yes, I understand that. And it is still often unclear to many and needs a good explanation, like yours.
finally, someone who knows what they are talking about and can teach
Almost 30years in the trade and I love your video. You keep my mind sharp thanks.
I always looked at it intuitively from the center point as the reference, where the difference between the two waves accounts for the greater amplitude. There is more area between the lines. A three phase system is truly out of phase, and from the difference between them at any point of time we can extract current. But of course one full winding has to be continuous.
Thank you for this videos! I appreciate all of your material! You have a great gift of putting the subject into terms that can be understood. I look forward to more videos in the future.
Wow! GREAT JOB! I have finally found someone that shows exactly what I have been saying for many years. When you try to explain this in a comment it is hard to get the point across! I have been saying that since oscilloscope is connected to neutral as common, it only looks like half is out of phase. You explained it perfectly. In phase to me is a point in time! And when someone says it is out of phase, it drives me nuts. I will be sharing this video with others.
LOL! I just wrote a very similar comment to yours! :grin: 👊
Great great video. Great presentation, great knowledge.
That couldn't have been explained any more clearly. Perfect!
Sick name
The best video so far on the subject
Thanks for explaining this. I have the delta 3 phase and did not understand how it worked. I use all of it on a 5hp pump but split off 2-120's for shop equipment.
Very nice description. Many others have mentioned your unusual US split phase system but not explained how it works. Thanks.
It was interesting to see in your practical demo the phase to phase light still lit even though you had removed the batteries to reverse them. The phase to neutral lights had extinguished but phase to phase still lit. A nice demonstration of leakage current that you might want to demonstrate some time.
Ur a great teacher. Ur explanations r great
As always in these 'paradoxes', it's the assumption(s) that are in conflict. In particular, for a voltage measurement, you have to define the relevant reference point for each measurement.
In this case we (I/you/they) can have two different views of which end of 'the other coil' is to be a reference. If we go with the centre tap as a common reference, the voltages are out of phase (opposite), while if we measure based on the diagram with 'top' end as the measurement, and the 'bottom' end as reference (which moves physically depending on coil), then we get the in-phase answer (for the Voltage!).
Check for the direction of current flow - in some arrangements (3 coils in sequence) you can get the current to flow the 'wrong way' (two + and one -, makes for a single + voltage to the load).
Great explanation by Dave.!
And remember it for any of the other paradoxes you bump into, all based on mistaken assumptions ;-)
Fantastic presentation. Really well explained and demonstrated. Thank you very much!
pretty much all you said is correct. You glossed over the fact that your clamp ammeter in DC would have given opposite signs if turned the other way around but that did not matter much for the point. Altogether, very clear if not exactly surprising for folks familiar with meters and scopes. Thank you. However, for safety reasons, I feel that you should have made a strong point at the end when discussing results from the ground lead of the scope to L2, that this should NOT be done in real life. It WILL BLOW UP your lead and/or scope because that would essentially be a dead short between L2 at 120V and mains ground through the scope's ground lead. As it stands, a curious person not familiar with scopes may just try that to verify your (correct) assertions and be in for a bad and dangerous surprise.
Great video. Your explanation of the phases helps to really see what's going on in real life. Thank you.
Not phases. We usually call them _legs_ because they are not different phases, and the legs are a metaphor for the entire secondary winding of the transformer.
Thank you so much for making this video! No other video I found explained the reference for the two sine waves before, and you really helped me have a lightbulb moment.
I believe my plain concept on current leading the voltage on distribution lines vs the voltage leads the current after the circuit breaker box in our homes is very great . Relating that to a city of service panels at different current (amperage) ratings we can see how much a town is using in current. And also how many circuit breakers we use in a breaker panel , 200 amp service can handle a quantity of 10 20 amp breakers at 120 / 240 volts each!
I very much enjoyed this video and its explanation of the output of a center tapped transformer. I particularly liked the example of flattening one sine wave to demonstrate a single phase of twice the amplitude. I understand that the output differs from say a three phase generator where the coils and rotation cause the phases to be physically sepearated by 120 degrees along the time axis, but I find arguing about the "in phase" of "out of phase" argument about household current about as useful as agruing whether a Zebra is white with black stripes or the reverse.
Once you understand how it works and what is happening I think the distinction is meaningless. The output of the center tapped transformer when referenced to neutral behaves exactly as two seperate mechanically produced phases would. I have always thought as the wave as "flipped" as opposed to shifted 180 degrees.
I would like to see an experiment where someone built a two phase generator running 180 degrees out of phase rather than the conventional 90 deg and hooked that output to three test points and then hooked the output of a center tapped to three others. With the sources of the power hidden. I wonder if it would be possible to identify which was which.
Thanks for a great video. I always find that thinking of things like this in as many ways, with as many examples as possible really helps to visualize what's actually going on.
Dave, love the videos and appreciate your amazing talent of teaching.
Hey thank you so much for the video I finally understand phase as it pertains to Transformers a little bit better now than I did before
I learned something here indeed. Good video.
Damn it. 20 years in the trade and this was always something I wondered about and you explained it in just a few minutes. Excellent video. I look forward to more!
The split phase setup is always single phase and neutral and live conductors have the same cross section.
Early true two-phase systems were 90º out of phase and if a neutral conductor (usually called ground back then) was used it had to have twice the cross section of the live conductors, otherwise otherwise two conductors were used for each phase. That system allowed to make simple AC motors that would start without the help of external devices like capacitors, it also allowed to easily change the direction of rotation of the motors.
Thanks Dave! I want to use this to illustrate to my kids. Brilliant illustration.
Excellent teaching of electrical eng'g.
I am an engineer but not by choice but culture, has never understood in school but you made it as “piece of cake”
Great video and I agree with everything you said except the terminology. L1 will always be 180° out of phase when compare to L2 and vice versa. If L1 is at +120 then L2 is -120. The in phase, out of phase terminology is really just a comparison to 3 phase to depict that L1 and L2 are always in sync with each other where in 3 phase power L1, L2 and and L3 are 120° apart
I agree with you. L1 and L2 have to be out of phase with one another would respect to their sine waves otherwise how would you measure any voltage between them.
What a brilliant demonstration!
Great job Dave!