I don't know what orifice my head has been in all my life but that was the best statement I have ever heard describing RMS ...... to make a static single measurement of a constant moving voltage. WOW! I'm stealing that line ...... thanks
When you pulled out that stretch band I thought that you where going loopy. But you showed the best demo I have ever seen for the 240 volt sign wave. After looking for a good answer on the internet and from people in the electrical business. You made It finally make scene. Thank You
I've been dealing with hooking power to our labs on drilling rigs for over 20 years and never has the 208 question mark been answered in a more clear way. All power on a rig is three phase, but we would only take two of the hots (single phase) to power our trailer. I do also remember seeing 220 volts on some rigs, but as I recall the single hots would be higher, as you've indicated. Thanks for clearing that up, At-Man.
Best explanation I've encountered!! All of sudden RMS, Peak voltage & why 208v 3-phase make sense. I came to this channel from a residential 3-phase power video that didntvexplain why the "High Leg" is 208v & an Ideal Circuit Analyzer video talking about Peak voltage & I didn't fully understand it. I didn't know 120v came from a special way of averaging!!! The only part that's unclear is how 208v is represented graphically. It was clear graphically for 240v--it's peak to peak of the 2 sine waves but 208v is not peak to peak. It is "somewhere" on the 2 waves, shoulder to shoulder so to speak but where exactly on those shoulders? Your channel is a welcomed surprise for a channel about machine shop work--not electrical. Great job.
Not drawn out at all, actually a really great answer I asked 2 journeymen one is usually great at explanations and he couldn’t do it this well. Awesome thanks so much ! Will be watching more
208v comes from the trig sin function between the 2 phases with a 120 degree phase relationship. (170v peak + 170v Peak) X sin(120 degree) = 294.4v peak, or 208v rms.
I do not understand where people started coming up with the term "split phase" and 180 degrees out of phase for single phase. A single phase 120/240 volt system has a single coil winding inside with a center of winding connection used as neutral. The number of windings sets voltage. So as the magnetic flux moves across the coils in the transformer secondary coils you get either 120 line to neutral or ground if grounded and 240 volts line to line. The sine waves are the exact same point in time just different voltages. By saying you add 120 v to 120 v is incorrect. L1 to L2 just is 240 v.the sine waves shown above and below the horizontal line at the same time are incorrect. Again single phase, one sine wave at one point in time.
Why the top wire of the top windings is 120v and the bottom wire of the second windings is 120v?? If what you are saying is right the bottom line of the second windings has to be 0v
Kevin, it all depends on how you look at it and what your reference is. Most people just see the neutral and two hot lines. They don't understand how transformers are wired and constructed. If you put both legs referenced to neutral on a two channel scope, you will get two sine waves 180 degrees out of phase. If you add a math channel to add the two channels together, you get a 240V rms signal.
At-Man Unlimited Machining If you put one 120 volt RMS signal on your scope, it is a simple sine wave. Correct? If you connect scope to L1 to L2 you get a simple sine wave with basically twice the amplitude. Correct? If you connect to 2 120 volt locations L1, L2, and N. you should get two sine waves exactly on top of each other. Is there a way to manipulate these waves to not be on top of each other for clarity? If so, then it is a false indicator. It is absolutely impossible for them to be out of sync with each other. One primary sine wave creates all secondary waves.
Molham Adawi I'm not exactly sure what you are asking. If a load is connected L1 to L2 the voltage is 240 volts. If the load is connected L1 to neutral it is 120 volts. If a load is connected L2 to neutral, it is 120 volts. If the neutral is grounded, meter connected either L1 or L2 to ground, is 120 volts. If a meter is connected neutral to ground it is zero volts. Make sense?
@@mmaad2165 The neutral is bonded to ground at the service disconnect, and ground is DEFINED AS zero volts. By extension, neutral is also at zero volts. The two ungrounded lines of a split phase system, are at equal and opposite voltages-to-ground. The voltage between them comes from the full scale quantity of secondary windings in the transformer. The voltage-to-neutral comes from half the secondary windings in the transformer due to the center tap. So we have the following equations that govern what the two line voltages are. The volt values are really RMS voltages, which is a special kind of averaging called root-mean-square. What really happens is there is a sine wave, that has a peak at sqrt(2)*the RMS voltage. | V1 - V2 | = 240V | V1 - VN | = 120V | V2 - VN | = 120V V1 = -V2 VN = 0
Thanks! My question was a bit different but this answered it, because I had always been told that in a three phase system the measurement from phase to phase was 220v. I guess I didn't pay enough attention at school and missed this important bit.
@@AtManUnlimitedMachining My doubt was why 220v had 180 degrees offset while 330v had 120, why did it change from 180 to 120? Magic? Now I understand that 220v(208v) in a 3 phase system still has 120 degrees offset. I kind of feel like an idiot lol
@@rigolfilo The 120 phasing is from transformer to transformer that comes directly from how a generator is wired with 120 degrees apart of rotation to generate the power. You get the 180 degree phasing on ONLY one transformer at a time by splitting the negative and positive charges right down the middle to completely oppose eachother since we're talking about alternating current.
Thank you for stating the facts!! Explained perfectly. I know an electrician who can’t understand the 220 V 180° out of phase. We argue about this here and then. He wants me to admit I’m wrong. He’s just one of those who thinks whatever he says is right. A true jester, fool. I learned the voltage phasing years ago in the USAF. Then the fool was in the army ..lol No pun of our Army guys. We all served to protect our great country, no matter what branch of service 👍
Excellent! Thank you! I’m actually in a machine shop class and I’m learning how to use the lathes and mills. I’m learning electrical as well. Looking forward to more videos!
Because I am in an old manufacturing zone, I have a true 240 Volt 3PH, 3 Wire Delta Service. Three balanced hots at 120V to ground. No ground wire. The conduit carries the ground. If I moved, I would have to use the 208V Wye service that you speak of At-Man. Because the 3 wire delta is not available in newer communities. Might still be available in the Buffalo area. Considering all the old Mfg. there. Also, under the 240 setup, a 10 HP 230V motor can make 10HP. Under 208 V, you are under volting so you will not make full rated HP. AND you will pull more amps which will make your meter count higher. Equaling a higher bill. I have to say I love my 3 wire Delta. I would not care for the all in one 208 Wye system. BTW. My 120/240 1PH is a separate service that comes in at the opposite end of the Bldg.
Yes, even here National Grid and NYSEG will no longer install a 240V Delta system. They are all switching everyone over to 208 Wye as far as I know. I very well could be wrong on that, but last I heard that was the case.
Fun fact. "Single phase" 120/208 from a WYE connected transformer is not really single phase if you include the neutral. I learned this after troubleshooting an overheating 3 phase motor in a facility. The "electrician" had hooked up a 208 3 phase motor to 2 of the hots and the neutral. It was starting but overheating, it was an easy troubleshoot and fix but I got to thinking, "How can a 3 phase motor start on single phase?" . If you think about it, two phases and a neutral from a WYE connected transformer give you some strange poly-phase with weird phase relations
Well the person who wired that is a total moron. Maybe that neutral gave it just enough bump to get the motor to rotate and start. Typically trying to start a 3phase motor with only 2 of the required phases doesn't work very well. And any electrician wiring 3 phase should be prepared to confirm the phasing is correct with the proper tools. Having certain 3 phase equipment run backwards without confirmation of proper phasing should have ruled out that a neutral was where it shouldn't have been.
277V is the phase-to-neutral conjugate voltage of 480V. In otherwords, the same 3-phase system has 480V between the phases, and 277V from any individual phase to neutral. Just like 120/208V, the ratio between them, is sqrt(3). Draw an equilateral triangle, 48 inches on each side. Find its center. Without a doubt, you'll measure 27.7 inches from that center to any corner. That's where the sqrt(3) comes from in this relationship. A general rule of understanding why we use higher voltages, is "voltage is cheap, current is expensive". You usually have to have enough "critical mass" of your power rating for this to hold true, but generally, it is more economical to use higher voltages for building high power devices and supplying power to them. In light commercial applications, the 208V is used for supplying power to high power appliances like the HVAC units, refrigeration, and motorized machinery, while the 120V is used for supplying power to receptacles and lighting that are a much smaller total of the power. In large commerical/industrial applications, many large scale loads require the 480V power. The 277V is commonly used for the lighting fixtures. A 277/480V service, will usually have a customer-owned transformer to produce 120/208V for the receptacle loads, and any other device needing a lower voltage. So you may have a 500kVA service at 277/480V for the building in general, while having 150kVA worth of 120/208V power on a separately derived system.
@@carultch this is fantastic. You did a better job at explaining this than most videos. Would you be able to explain how you get 208v out of a single phase service? All I have seen is that 208 comes from 3 phase with each phase having 120. How do you get 208 from a single phase 120/240?
@@realSamAndrew The short answer is, that you don't directly get 208V from 120/240V single phase. Not without a transformer. I can't think of a reason you would want to do this in the first place. There are loads that work on both 208V and 240V, so maybe that is what you have in mind. Common for big-ticket residential loads, like ovens and dryers. The 208V or 240V will run the heating element that is less voltage sensitive than the motor, while the motor would run on 120V (since it is less Watt-intensive, and the 120V is what these two grids have in common. These loads work better on 240V, because otherwise you'd only run at 75% power (i.e. 83% Voltage * 83% current). A motor load like that of an A/C system would need a physical adjustment of its coil taps, so that it can work on 208V instead of 240V. If you run motors on too little voltage than their rating requires, this could lock the rotor and damage the motor. My split-phase Geogebra resource: www.geogebra.org/m/qsz3twyg Burgundy = the 240V across the red and black wires Black = Line 1 at 120V to neutral. Red = Line 2 at 120V to neutral, opposite polarity from line 1.
@@realSamAndrew Another kind of "single phase 208V" is the kind that feeds apartment buildings. The property gets a 3-phase service in the aggregate, which divides into sub-services for each dwelling unit. Usually, there is also a common loads service at 3-phase, for running general loads like exterior and hallway lights. Each dwelling unit gets a staggered pair of phases (staggered from what each neighbor gets), and the neutral. The dwelling unit therefore gets two live conductors that are 208V apart, and each 120V to neutral. I dislike the term "single phase" for this, but nevertheless, that is what the industry calls it. My preferred term is "open wye", since it is a partial grid from the 120/208V wye grid. There is no 240V brought to the dwelling, and using 208V instead of 240V has to be considered when big ticket loads are selected for the application. I would also instinctively call this "2-phase", but that is reserved for an obsolete system.
@@carultch @carl thank you very much. Would this "2 phase" 208 system require a motor capacitor that is eliminated on true 3 phase? I watched an HVAC video today with a system having 208 service and it had a failed capacitor. Small commercial bldg and no details on whether the power was single or 3 phase. Can provide link if you want.
NIce explanation, but the analogy with the exercise band is not correct because if the red dot is a zero for both, then each hand has to cross over that dot going from +120V to -120V. Not the way it's show on the video. If the red dot represent -120V for one hand and +120V for another hand (that's how it was explained on the video) - then the maximum difference between two hands is 480V (when the phases difference between the hands is 180 degrees).
The transformer is not out of phase with itself, but when you cut the 240V single-phase secondary in half, you get two 120V waveforms, and when you reverse one, they are in opposite phase. That is equivalent to 180° out of phase. He does know what he is talking about, you just don’t like his terminology.
@@GH-oi2jf I am not talking about what I like or don't like. I was talking from how I learned it and it was said that in single phase there is only one "phase" but since there is a center tapped neutral, the polarities are opposite. I didn't say he doesn't know what he's talking about.
@@illestofdemall13 - Vladimir said he doesn’t know what he is talking about. I responded to both in one reply. I apologize for being lazy, but stand by my opinion that “opposite phase” is a legitimate way to characterize the situation.
@@GH-oi2jf Nothing wrong with standing by your opinion. I may have been fussy with semantics. I have OCD so sometimes I can be that way without meaning to.
The star (delta) transformer is basically an obsolete method of supplying 3 phase power. Reason being: Only one spot to tap for 120v between the 3 transformers which leaves a big load on one transformer to supply 120v to the building. There is other issues, but this is the main one. Whereas a Y transformer arrangement for 3 phase will allow all 3 transformers the ability to provide 120v to the building and it can be dispersed more equally to keep the loads similar to all 3 transformers.
Great vid, I am young guy (26) in commercial refrigeration, so all I work with is 120/208v. This video was informative, but you didn't really explain why the 208 voltage is necessary, which is because of 3 phase. A normal person after watching this video will still wonder "if the goal is to still try and get 120v for standard equipment why exactly can't you just run split phase power?" You should have elaborated that 3 phase power is necessary for certain types of refrigeration and manufacturing equipment. So the real answer of why 120/208v is so great is because you can run 120v, 208v single phase and 208v three phase equipment all from the same breaker panel. You also have significantly more space for single pole breakers on a 120/208 three phase vs 120/240 split phase breaker box
@@AtManUnlimitedMachining Thanks for the reply, sorry I did not know. I just subscribed to your channel and saw the original video, very well done , you seem well educated.
@@AnUnapologeticApologist Good question. The short answer is "voltage is cheap, current is expensive". Voltage you "pay for" with insulators, such as plastic, ceramics, and air. Current, you "pay for" with conductors, such as copper, silver, aluminum, and semiconductors. For major loads, it is important to build them to operate off of as high of a voltage as practical. This means less wire in the circuit that supplies them, and less "mass" to the conductive components within the device. There is a trade-off, because a device has to be large enough for "voltage to be cheaper than current". A critical mass, if you will, which is why smaller scale loads generally tend to run on 120V. Consider your kilowatt-intensive loads, such as HVAC devices, commercial refrigerators, motorized machinery, heaters. It is more cost effective to build these devices to run off of 208V, than it is to build them for 120V. It is also more cost-effective to build your circuit and service that supplies power to them. It would be even more cost effective to build higher scale devices for 480V, which is why you see 277/480V services on larger scale industrial applications. Your general lighting and receptacles by contrast, is a lot less of the total kilowatts of your building. And in many cases, are only built for 120V supply circuits.
@@carultch if you read my comment I was actually addressing an unanswered question not really asking the question myself. Its common knowledge in electrical that more voltage means the same work with less amp draw. Another advantage with not single phase but 3 phase is eliminating start components which can mean less service calls overall
Splitting a single phase 240 service does not create two legs 180 degrees out of phase. Measuring from a center tap to each hot is simply half the voltage with the order of the leads reversed. In other words it measures the opposite polarity, not 180 out of phase. Phase is a shift in time. 3 phase power is truly 3 waves shifted in time by the physical placement of the generating coils 120 degrees apart on the rotor.
What is the point in making this video with incorrect terminology? I just explained the difference. That is not “equivalent”. What you mean to say is that they have an equivalent result. Phase and polarity are not the same thing. Using them interchangeably just leads to misconceptions. That’s when you get people talking about 2 phase power which doesn’t even exist. If there was a point to this video there certainly is a point to clarifying the terminology.
@@timbrackett1518 - It’s not incorrect terminology. It is just a way of looking at it. “Polarity” is incorrect terminology when speaking of AC, in my opinion. That is a DC term. For AC, we say “opposite phase” instead of “opposite polarity.”
@@GH-oi2jf Sorry the terminology is incorrect. You go look up definitions for phase and polarity. Then come back and tell me again they are the same. They are not! No one cares about your opinion. You come here just to argue? I commented because this “educational video” uses misleading terminology. You commented to argue.
@@GH-oi2jf Phase is a shift of sine wave form. It is not just "opposite polarity". To have real 180 degrees out of phase you would need one sets of wires coming from N-L2 to be longer than wires from N-L1 (or other way around). And because we are talking about 60Hz grid then difference in length should be around half of the wavelength of it. It means: *λ = v/f = (c * VoP)/f* (.82 * 300000km/s) / 60Hz = 4100km = 2548 miles. Half of it is 1273.81 miles. I bet you that you usually don't have that much of wiring in an average house. -------- *λ* wavelength *v* speed of wave propagation *f* frequency *c* speed of light in vaccum *VoP* velocity of propagation expressed in %. For typical copper wires it's something between 80 to 90% of c.
It would only be coming from one of the 3 phases after a step down transformer at the hydro pole. The single phase is a SPLIT phase of only one leg of a 3 phase system. One waveform is negative, the other is positive at 180 degrees apart... You can see this in every residential area with visible hydro poles. You will see 1 transformer tied in to one of the 3 wires above to serve residential dwellings... When you see a cluster of 3 transformers close together, that's your 3 phase that is going to be feeding a commercial business/factory.
High-leg delta is a bad system. Symmetrical load is almost impossible. Here in Europe, every household gets 230/400V three-phase power. 230V 1p for normal appliances and 400V 3p for every device above 4kW.
So the 240vac single phase is NOT split-phase. the 60hz waveform does not split. What is happening is the transformer is made to output 240vac and is completely electrically isolated from the input or any other line. then a tap is made in the middle of the winding, like on a welder transformer that has multiple taps. We call that tap neutral and because it is in the middle of the winding it gives 120vac from neutral to each line. So the graph showing two separate waves 180 degrees apart from each other is wrong. it's a single wave form of 240vac.
"Neutral" means connected to ground. The center tap of the secondary is grounded, as is the common line of the wye distribution line. The primary and secondary are not completely electrically isooated because the neutrals are connected.
So it seems by looking at the comments everyone else is understanding and I am just confused 😡what formula did you use for single phase 180 degrees out of phase when you got 240??? I don’t see how you add there? I thought they were both IN PHASE and then you add 120+120 , you get 240. If they are really out of phase then it’d be called 2 phase no? Basically the question I’ve been searching for my whole career and i can’t seem to find anyone who can explain it in a way I understand .I’ve already spent two hours tonight researching again . My question has been : why is it called single phase when there are two wires that according to you are out of phase. If they were in phase then calling it single phase would make a lot of sense
Think of it like taps on a transformer..its the potential difference between different points one 240 v coil. The 180 degrees out of phase makes no sense.
hi at-man please record one clip about complete axis motor repair and amp adjust gain setting and balance setting also clock card adjustment and powersupply check thx a lot 🙋
Can 120/ 208v 3 phase generator power a 230v 1 phase welder without modification has 4 prong 120/208v 20amp receptacle beside getting an adpator from 3 prong welder plug to 4 prong from generator?
I have an electronic dimming switch. It's powered by an L14-20 Plug. The device itself is a 120v device - Half of of the circuits its providing is powered by a 20AMP leg, as is the other. This is context so you don't say the following is absurd and dangerous. Often times, because the L14-20 is not accessible, I use a reverse Y-Splitter (x2 Male Edisons, combined into one female L14-20 Connector). I plug the x2 male edisons into two breakers, knowing they are on different breakers and PHASES. My question: Is there any disadvantage to plugging the two edisons onto different breakers, but the same phase? The advantage is accessibility.
If you plug them into the same phase you can over load the neutral line. For example, if both hot legs are in phase but on separate 20 amp breakers, you will be able to draw a total of 40 amps. Because there in phase the current will sum at the neutral and 40 amps will be on the neutral. Assuming you used the same size wire for all connections it will overload the neutral. When there on separate phases and each hot leg is carrying 20 amps then the neutral current in an ideal system would be zero.
The third wire is the neutral (or it could be a ground). If you have 240V equipment only, you don't need the neutral. But some 240V equipment contains some 120V components. In that case, you need the neutral.
At 7:50, you mentioned that for 120v, three phase system, a one leg would be higher than 120v and needs to be stepped down. Could you please clarify? My understanding is that the 208v came from 120v with three phases , each phase is 120 degree apart. The line to neutral would be 120v. Thank you.
He didn’t say that. He said if you had 220V 3-phase, the voltage phase-to-neutral would be too high, much more than 120. You want to have 120V service, so that requires that for 3-phase, the phase-to-phase voltage will be 208V.
@@AtManUnlimitedMachininggreat video! still have one question. 240v 3 phase system, If you are reading 208v from leg to leg, and 120v from leg to neutral, can you still read 240v ?
That does not have a straight forward answer. If you have a 208, Y connected service, there will be 120 leg to neutral. There is a service called a "high leg Delta" in which you get 240V leg to leg and its connected in a delta. They then add a center tap to one of the windings on the transformer to provide 120. This configuration has a major drawback of phase imbalance issues. The 120V loads can only be on one phase of the 3 phase system. With a 208/120 Y connection you can balance the 120 loads on all 3 phases.
In relation to neutral yes. Not in relation to each other. To measure to eachother, the calculation is subtractive, since voltage is potential *difference.* -120-120=-240.
Great video! A follow up, are all modern 3-phase systems 208V? That is, if I got a 3 phase connect to support an EV Charger would my home now be more like a commercial property where the 240V dryer seems slow?
The utilities like to install 208 3 phase for light commercial applications. It depends on your provider, but I don't think they are installing to many 240 3 phase services new anymore.
Most Informative - Thank you. Clarification question: From the description you gave, I would have thought that in the demonstration (reference 4:24 to 4:30 in the video ) that it would have been +180V then -180V (or more precisely +169.71V then -169.71V) versus the used reference of +120 then -120 {if measuring actual voltage} OR if you are measuring Vrms - then the reference to rms was simply left off in the video during those seconds and thus the 120V was actually 120Vrms??? Can you please clarify? Thank you kindly.
Great video. Can you tell me how to wire a high bay metal halide fixture (120v,208v,240v,277v) to a.. I think a split phase (2 hots at 120v each and a physical ground)? I have not been able to get it to turn on it just buzzes. I wired a 277v to a hot, a common to the other hot and the physical ground green. Any help is greatly appreciated
I have a 240 volt that has 3 wires. A black, a white and a ground. I want to run a 120 volt from this. The 120 volt has a white a black and a ground as well. How do I do this?
Get a single phase step-down transformer, with a KVA rating appropriate for your application. Configure it for 240V on the primary, and 120V on the secondary. You probably are located in a country where the mains voltage is 240V to neutral and 415V phase-to-phase, and they don't even supply 120V to the typical customer.
They don’t. Nowhere in an electrical system do you combine 120v lines. 120v lines come from splitting a single phase 240v service or from one leg of a 3 phase 208v service.
Yeah, didn't answer my question. So how come when I attache oscilloscope to 120 volts I will see one sine wave, when I attache scope to 240 volts I will see one sine wave. Is the scope stupid it doesn't see two sine waves? Thanks
Because the explanation is inaccurate. Spitting 240 doesn’t create 2 phases out of 1 as was implied. If you measure from the neutral to each leg you are measuring 2 different polarities as you have changed the order of the leads.
Kindly explain why, WITH NO OPEN NEUTRAL, some current (unbalanced portion) does travel back to the center tap AND also some VOLTAGE must move it. I have NO SHOCK when touching the GUY wire outside of the property, going to the transformer? Thank you.
The neutral is referenced to ground. If your grounded and measure the neutral there should be no voltage difference. However, if you disconnect the neutral from a load and measure the loads neutral terminal you WILL get voltage because your completing the path to ground. This is why we use a 3 wire system with an independent ground wire and the Neutral and ground is only tied at one point in the main panel.
At-Man Unlimited Machining Wonderful explanation of KVL Kirchhoff's voltage law. Open the neutral at a load, measure for voltage, your meter BECOMES AN ADDITIONAL LOAD. thank you.
Oh yeah, that graph is wrong too. The graph with 2 “out of phase” 120v sine waves? That graph shows Zero voltage. Since when does 120v plus -120v equal 240v? You keep saying “add two 120v legs”. Nowhere ever are two 120v lines tied together to make 240v. 240v is split. You didn’t shift anything in time. Both haves are still in phase. You are just measuring each side from the middle. In doing so you are reversing the order of the leads on one side compared to the original 240v.
The graphs are in reference to the neutral and it is a correct example. This is exactly how we measure 240 volts. If you graphed it using “A” phase as your reference, you’d have two sine waves. One twice as big as the other, and they would be in phase with peaks at the same points. You would still measure 120 and 240 RMS.
So I have a question. I am in Taiwan, and my house/shop has a 3 phase supply. When I measure across any of the phases, I get 235 volts. However all 120v appliance is running through a transformer. What kind of system is this? Why is the transformer necessary, and why can't I just take one of the legs and run the neutral to ground?
Because you have 235VAC from phase to phase, even if your connection was a WYE you would get 136VAC from phase to neutral. The transformer steps the phase voltage down from 235 to 120 for you.
@@AtManUnlimitedMachining So 220v appliances are more forgiving of voltage variations? As in 135v is going to burn stuff while for 220v counterpart it's not as critical? Because standard 220v appliance works fine connecting between phases but 110v doesn't. It seems like a weird system to require a transformer to get 110. In a 2 phase system in Taiwan when I measured across 220 I get 250v. Do they have different power plants putting out 1 phase vs 3 phase systems, because it seems the waveform is different, or how do they split it at the substation? My understanding is electricity comes out of a power plant as 3 phase...
@@taiwanluthiers It's not different power plants putting out the different systems. It is the topology of the service transformer. Three phase comes from three magnetic couplings in the transformer between the utility's feeder, and the secondary they give to you to connect your service conductors. Single phase comes from just one of the phases on the utility's feeder, a single magnetic coupling in the transformer, and if it is a split phase system, they center-tap it to make two lines with equal and opposite voltage-to-neutral. Grid voltage also is a moving target, and it is a challenge for utilities to maintain a stable nominal voltage at your service. When a lot of load is present in your neighborhood, the voltage drops. When load diminishes, voltage rises. There are taps on the transformers that allow for moderate adjustments in grid voltage, to adapt to variations as new customers come online and substations are upgraded.
Hello Jim, transformers are pretty straight forward, a primary and a secondary. From there the name plate and mfgr info will tell you how to wire it depending on your incoming voltage and your desired output voltage.
I have a 3 phase 30 amp requirement for a water distiller but my house is the typical us single not a 3 phase. Can I still hook up machine by using three 30 amp single breakers or two doubles?
Hi! Why both peak at same time can measure 240? If they peak together there isn’t voltage potential difference between two leg still can measure voltage? I don’t get that, please explain thanks
I have a Geogebra resource that answers this: www.geogebra.org/m/qsz3twyg The black wave indicates the voltage vs time waveform on line 1 (the black conductor) to neutral. The red wave indicates the voltage vs time waveform on line 2 (the red conductor) to neutral. The burgundy wave indicates black minus red, which is the voltage across the two line conductors. At any given time Burgundy Voltage = black Voltage minus red Voltage. It's not the voltage to ground that you measure black-to-red. It's the inter-phase voltage, that the burgundy waveform measures
In theory, it could exist, where it is 480V phase-to-phase, and 240V phase-to-neutral on phases A and C. This would make the B-phase high leg 416 Volts to neutral. However, there is simply no application of such a grid. The delta topologies on a 480V system are usually either corner-grounded delta, or ungrounded delta.
If you have a generator putting out 480v going to a transformer that says 277/480 Y on it, does that mean its stepping it down to 277? Or is that the rated input voltage to the transformer?
A transformer labeled 277/480 Y will have a neutral point. If you measure voltage between two of the hot legs you will get 480V, if you measure the voltage from one hot leg to the neutral leg you will get 277V. You will find a lot of commercial lighting uses 277V so they can run on one leg of 480 without the need for another transformer.
I don't know what orifice my head has been in all my life but that was the best statement I have ever heard describing RMS ...... to make a static single measurement of a constant moving voltage. WOW! I'm stealing that line ...... thanks
When you pulled out that stretch band I thought that you where going loopy. But you showed the best demo I have ever seen for the 240 volt sign wave. After looking for a good answer on the internet and from people in the electrical business. You made It finally make scene. Thank You
Your welcome, I do have some odd methods, but they seem to be working well!
This is the stuff they don't teach you, or atleast don't teach you well in trade school. This is so simple, yet so effective
That is the answer I've been looking for since I graduated in my college. Thank you!
I've been dealing with hooking power to our labs on drilling rigs for over 20 years and never has the 208 question mark been answered in a more clear way. All power on a rig is three phase, but we would only take two of the hots (single phase) to power our trailer. I do also remember seeing 220 volts on some rigs, but as I recall the single hots would be higher, as you've indicated. Thanks for clearing that up, At-Man.
Welcome!
Best explanation I've encountered!! All of sudden RMS, Peak voltage & why 208v 3-phase make sense. I came to this channel from a residential 3-phase power video that didntvexplain why the "High Leg" is 208v & an Ideal Circuit Analyzer video talking about Peak voltage & I didn't fully understand it. I didn't know 120v came from a special way of averaging!!! The only part that's unclear is how 208v is represented graphically. It was clear graphically for 240v--it's peak to peak of the 2 sine waves but 208v is not peak to peak. It is "somewhere" on the 2 waves, shoulder to shoulder so to speak but where exactly on those shoulders? Your channel is a welcomed surprise for a channel about machine shop work--not electrical. Great job.
Not drawn out at all, actually a really great answer I asked 2 journeymen one is usually great at explanations and he couldn’t do it this well. Awesome thanks so much ! Will be watching more
You've very wide knowledge and good teaching skills, sir. Thank you for this superb explanation.
Thanks
208v comes from the trig sin function between the 2 phases with a 120 degree phase relationship. (170v peak + 170v Peak) X sin(120 degree) = 294.4v peak, or 208v rms.
thanks!!!
Just make sure your calculator is set to DEGREES if you're doing it on your phone haha
Best explanation of this concept I have ever seen.
Best explanation of this I ever heard
Excellent video, and demonstration/graphs! thank you for your clear and precise explanation!
I do not understand where people started coming up with the term "split phase" and 180 degrees out of phase for single phase. A single phase 120/240 volt system has a single coil winding inside with a center of winding connection used as neutral. The number of windings sets voltage. So as the magnetic flux moves across the coils in the transformer secondary coils you get either 120 line to neutral or ground if grounded and 240 volts line to line. The sine waves are the exact same point in time just different voltages. By saying you add 120 v to 120 v is incorrect. L1 to L2 just is 240 v.the sine waves shown above and below the horizontal line at the same time are incorrect. Again single phase, one sine wave at one point in time.
Why the top wire of the top windings is 120v and the bottom wire of the second windings is 120v??
If what you are saying is right the bottom line of the second windings has to be 0v
Kevin, it all depends on how you look at it and what your reference is. Most people just see the neutral and two hot lines. They don't understand how transformers are wired and constructed. If you put both legs referenced to neutral on a two channel scope, you will get two sine waves 180 degrees out of phase. If you add a math channel to add the two channels together, you get a 240V rms signal.
At-Man Unlimited Machining If you put one 120 volt RMS signal on your scope, it is a simple sine wave. Correct? If you connect scope to L1 to L2 you get a simple sine wave with basically twice the amplitude. Correct? If you connect to 2 120 volt locations L1, L2, and N. you should get two sine waves exactly on top of each other. Is there a way to manipulate these waves to not be on top of each other for clarity? If so, then it is a false indicator. It is absolutely impossible for them to be out of sync with each other. One primary sine wave creates all secondary waves.
Molham Adawi I'm not exactly sure what you are asking. If a load is connected L1 to L2 the voltage is 240 volts. If the load is connected L1 to neutral it is 120 volts. If a load is connected L2 to neutral, it is 120 volts. If the neutral is grounded, meter connected either L1 or L2 to ground, is 120 volts. If a meter is connected neutral to ground it is zero volts. Make sense?
@@mmaad2165 The neutral is bonded to ground at the service disconnect, and ground is DEFINED AS zero volts. By extension, neutral is also at zero volts.
The two ungrounded lines of a split phase system, are at equal and opposite voltages-to-ground. The voltage between them comes from the full scale quantity of secondary windings in the transformer. The voltage-to-neutral comes from half the secondary windings in the transformer due to the center tap.
So we have the following equations that govern what the two line voltages are. The volt values are really RMS voltages, which is a special kind of averaging called root-mean-square. What really happens is there is a sine wave, that has a peak at sqrt(2)*the RMS voltage.
| V1 - V2 | = 240V
| V1 - VN | = 120V
| V2 - VN | = 120V
V1 = -V2
VN = 0
Great, great explanation, you should do a podcast or become a teacher
Best explanation I've seen of this yet
Excellent explanation sir. I sometimes confuse about this too and now I understand it. Thank you.
Thanks!
My question was a bit different but this answered it, because I had always been told that in a three phase system the measurement from phase to phase was 220v.
I guess I didn't pay enough attention at school and missed this important bit.
There are three phase systems out there with a line to line of 220, more common to find 208 now.
@@AtManUnlimitedMachining My doubt was why 220v had 180 degrees offset while 330v had 120, why did it change from 180 to 120? Magic? Now I understand that 220v(208v) in a 3 phase system still has 120 degrees offset.
I kind of feel like an idiot lol
@@rigolfilo The 120 phasing is from transformer to transformer that comes directly from how a generator is wired with 120 degrees apart of rotation to generate the power. You get the 180 degree phasing on ONLY one transformer at a time by splitting the negative and positive charges right down the middle to completely oppose eachother since we're talking about alternating current.
First video of yours I've seen but that last bit about FIRST robotics at the end made me a subscriber 🦾
Very clear. I am an engineer, not an electrical one, when i always wondered.
I feel vindicated, I just explained this to a co-worker today and I was correct! I have no idea how I knew this.. Great video Sir!
Thanks! Good for water cooler talk.
Thank you for stating the facts!! Explained perfectly. I know an electrician who can’t understand the 220 V 180° out of phase. We argue about this here and then. He wants me to admit I’m wrong. He’s just one of those who thinks whatever he says is right. A true jester, fool. I learned the voltage phasing years ago in the USAF. Then the fool was in the army ..lol No pun of our Army guys. We all served to protect our great country, no matter what branch of service 👍
Thanks! There were a few other tidbits I was able to gather from this one video-
I'm am an electrican and that was well said sir bravo.
Excellent! Thank you! I’m actually in a machine shop class and I’m learning how to use the lathes and mills. I’m learning electrical as well. Looking forward to more videos!
Great video and explanation! Thanks for explaining so clearly and concisely.
Welcome
Because I am in an old manufacturing zone, I have a true 240 Volt 3PH, 3 Wire Delta Service. Three balanced hots at 120V to ground. No ground wire. The conduit carries the ground. If I moved, I would have to use the 208V Wye service that you speak of At-Man. Because the 3 wire delta is not available in newer communities. Might still be available in the Buffalo area. Considering all the old Mfg. there. Also, under the 240 setup, a 10 HP 230V motor can make 10HP. Under 208 V, you are under volting so you will not make full rated HP. AND you will pull more amps which will make your meter count higher. Equaling a higher bill. I have to say I love my 3 wire Delta. I would not care for the all in one 208 Wye system. BTW. My 120/240 1PH is a separate service that comes in at the opposite end of the Bldg.
Yes, even here National Grid and NYSEG will no longer install a 240V Delta system. They are all switching everyone over to 208 Wye as far as I know. I very well could be wrong on that, but last I heard that was the case.
Great video, you are a very good teacher, thank you for explaining this so well!
good job Sir!
Rocky
THAT, was an Outstanding Explanation !!!
Fun fact. "Single phase" 120/208 from a WYE connected transformer is not really single phase if you include the neutral. I learned this after troubleshooting an overheating 3 phase motor in a facility. The "electrician" had hooked up a 208 3 phase motor to 2 of the hots and the neutral. It was starting but overheating, it was an easy troubleshoot and fix but I got to thinking, "How can a 3 phase motor start on single phase?" .
If you think about it, two phases and a neutral from a WYE connected transformer give you some strange poly-phase with weird phase relations
Well the person who wired that is a total moron. Maybe that neutral gave it just enough bump to get the motor to rotate and start. Typically trying to start a 3phase motor with only 2 of the required phases doesn't work very well. And any electrician wiring 3 phase should be prepared to confirm the phasing is correct with the proper tools. Having certain 3 phase equipment run backwards without confirmation of proper phasing should have ruled out that a neutral was where it shouldn't have been.
Good stuff right here. Exactly what I needed.
A follow up video of the differences between 480v 277v & 208v would be interesting
277V is the phase-to-neutral conjugate voltage of 480V. In otherwords, the same 3-phase system has 480V between the phases, and 277V from any individual phase to neutral. Just like 120/208V, the ratio between them, is sqrt(3). Draw an equilateral triangle, 48 inches on each side. Find its center. Without a doubt, you'll measure 27.7 inches from that center to any corner. That's where the sqrt(3) comes from in this relationship.
A general rule of understanding why we use higher voltages, is "voltage is cheap, current is expensive". You usually have to have enough "critical mass" of your power rating for this to hold true, but generally, it is more economical to use higher voltages for building high power devices and supplying power to them. In light commercial applications, the 208V is used for supplying power to high power appliances like the HVAC units, refrigeration, and motorized machinery, while the 120V is used for supplying power to receptacles and lighting that are a much smaller total of the power. In large commerical/industrial applications, many large scale loads require the 480V power. The 277V is commonly used for the lighting fixtures. A 277/480V service, will usually have a customer-owned transformer to produce 120/208V for the receptacle loads, and any other device needing a lower voltage. So you may have a 500kVA service at 277/480V for the building in general, while having 150kVA worth of 120/208V power on a separately derived system.
@@carultch this is fantastic. You did a better job at explaining this than most videos. Would you be able to explain how you get 208v out of a single phase service? All I have seen is that 208 comes from 3 phase with each phase having 120. How do you get 208 from a single phase 120/240?
@@realSamAndrew The short answer is, that you don't directly get 208V from 120/240V single phase. Not without a transformer. I can't think of a reason you would want to do this in the first place.
There are loads that work on both 208V and 240V, so maybe that is what you have in mind. Common for big-ticket residential loads, like ovens and dryers. The 208V or 240V will run the heating element that is less voltage sensitive than the motor, while the motor would run on 120V (since it is less Watt-intensive, and the 120V is what these two grids have in common. These loads work better on 240V, because otherwise you'd only run at 75% power (i.e. 83% Voltage * 83% current). A motor load like that of an A/C system would need a physical adjustment of its coil taps, so that it can work on 208V instead of 240V. If you run motors on too little voltage than their rating requires, this could lock the rotor and damage the motor.
My split-phase Geogebra resource:
www.geogebra.org/m/qsz3twyg
Burgundy = the 240V across the red and black wires
Black = Line 1 at 120V to neutral.
Red = Line 2 at 120V to neutral, opposite polarity from line 1.
@@realSamAndrew Another kind of "single phase 208V" is the kind that feeds apartment buildings. The property gets a 3-phase service in the aggregate, which divides into sub-services for each dwelling unit. Usually, there is also a common loads service at 3-phase, for running general loads like exterior and hallway lights.
Each dwelling unit gets a staggered pair of phases (staggered from what each neighbor gets), and the neutral. The dwelling unit therefore gets two live conductors that are 208V apart, and each 120V to neutral. I dislike the term "single phase" for this, but nevertheless, that is what the industry calls it. My preferred term is "open wye", since it is a partial grid from the 120/208V wye grid. There is no 240V brought to the dwelling, and using 208V instead of 240V has to be considered when big ticket loads are selected for the application.
I would also instinctively call this "2-phase", but that is reserved for an obsolete system.
@@carultch @carl thank you very much. Would this "2 phase" 208 system require a motor capacitor that is eliminated on true 3 phase?
I watched an HVAC video today with a system having 208 service and it had a failed capacitor. Small commercial bldg and no details on whether the power was single or 3 phase. Can provide link if you want.
NIce explanation, but the analogy with the exercise band is not correct because if the red dot is a zero for both, then each hand has to cross over that dot going from +120V to -120V. Not the way it's show on the video. If the red dot represent -120V for one hand and +120V for another hand (that's how it was explained on the video) - then the maximum difference between two hands is 480V (when the phases difference between the hands is 180 degrees).
Great explanation. 👍
1.73 is square root of 3 1.41 is square root of 2 208 /1.73 =120 great video
Thanks this info help to connect 1 phase 208 volts motor @ 26 Amps.
Welcome
Great way to explain things!! 👍👍👍
Really good explanation!
Kinda like a 4-cylinder engine; where the pistons are 90° offset from each other. Thanks
In a way, yes
Wonderful explanation
Awesome video thank you !
Thanks for the explanation man.
Yes but you would still need a buck-boost transformer to obtain 240 volts to operate some equipment.
They are opposite polarity but not really 180 degrees out of phase. You can't have a single phase transformer be out of phase with itself.
I think he doesn’t know what he is talking about.
The transformer is not out of phase with itself, but when you cut the 240V single-phase secondary in half, you get two 120V waveforms, and when you reverse one, they are in opposite phase. That is equivalent to 180° out of phase. He does know what he is talking about, you just don’t like his terminology.
@@GH-oi2jf I am not talking about what I like or don't like. I was talking from how I learned it and it was said that in single phase there is only one "phase" but since there is a center tapped neutral, the polarities are opposite. I didn't say he doesn't know what he's talking about.
@@illestofdemall13 - Vladimir said he doesn’t know what he is talking about. I responded to both in one reply. I apologize for being lazy, but stand by my opinion that “opposite phase” is a legitimate way to characterize the situation.
@@GH-oi2jf Nothing wrong with standing by your opinion. I may have been fussy with semantics. I have OCD so sometimes I can be that way without meaning to.
Great explanation, thx
Very informative. Could of shown the star transformer (with neutral) and shown
the math to reach 208 volts. Thank you. Wonderful video.
The star (delta) transformer is basically an obsolete method of supplying 3 phase power. Reason being: Only one spot to tap for 120v between the 3 transformers which leaves a big load on one transformer to supply 120v to the building. There is other issues, but this is the main one. Whereas a Y transformer arrangement for 3 phase will allow all 3 transformers the ability to provide 120v to the building and it can be dispersed more equally to keep the loads similar to all 3 transformers.
@@Jason-wc3fh What's the difference between a star transformer arrangement and a WYE transformer arrangement?
Great vid, I am young guy (26) in commercial refrigeration, so all I work with is 120/208v. This video was informative, but you didn't really explain why the 208 voltage is necessary, which is because of 3 phase. A normal person after watching this video will still wonder "if the goal is to still try and get 120v for standard equipment why exactly can't you just run split phase power?" You should have elaborated that 3 phase power is necessary for certain types of refrigeration and manufacturing equipment. So the real answer of why 120/208v is so great is because you can run 120v, 208v single phase and 208v three phase equipment all from the same breaker panel. You also have significantly more space for single pole breakers on a 120/208 three phase vs 120/240 split phase breaker box
Thanks, I made other videos that cover 3 phase, this was more in response to a question someone had on how the math works out.
@@AtManUnlimitedMachining Thanks for the reply, sorry I did not know. I just subscribed to your channel and saw the original video, very well done , you seem well educated.
Thanks, been around the block a few times, no worries.
@@AnUnapologeticApologist Good question. The short answer is "voltage is cheap, current is expensive". Voltage you "pay for" with insulators, such as plastic, ceramics, and air. Current, you "pay for" with conductors, such as copper, silver, aluminum, and semiconductors.
For major loads, it is important to build them to operate off of as high of a voltage as practical. This means less wire in the circuit that supplies them, and less "mass" to the conductive components within the device. There is a trade-off, because a device has to be large enough for "voltage to be cheaper than current". A critical mass, if you will, which is why smaller scale loads generally tend to run on 120V.
Consider your kilowatt-intensive loads, such as HVAC devices, commercial refrigerators, motorized machinery, heaters. It is more cost effective to build these devices to run off of 208V, than it is to build them for 120V. It is also more cost-effective to build your circuit and service that supplies power to them. It would be even more cost effective to build higher scale devices for 480V, which is why you see 277/480V services on larger scale industrial applications.
Your general lighting and receptacles by contrast, is a lot less of the total kilowatts of your building. And in many cases, are only built for 120V supply circuits.
@@carultch if you read my comment I was actually addressing an unanswered question not really asking the question myself. Its common knowledge in electrical that more voltage means the same work with less amp draw. Another advantage with not single phase but 3 phase is eliminating start components which can mean less service calls overall
Splitting a single phase 240 service does not create two legs 180 degrees out of phase. Measuring from a center tap to each hot is simply half the voltage with the order of the leads reversed. In other words it measures the opposite polarity, not 180 out of phase. Phase is a shift in time. 3 phase power is truly 3 waves shifted in time by the physical placement of the generating coils 120 degrees apart on the rotor.
Opposite polarity is equivalent to a 180° phase shift. There is no point in quibbling about the terminology.
What is the point in making this video with incorrect terminology? I just explained the difference. That is not “equivalent”. What you mean to say is that they have an equivalent result. Phase and polarity are not the same thing. Using them interchangeably just leads to misconceptions. That’s when you get people talking about 2 phase power which doesn’t even exist. If there was a point to this video there certainly is a point to clarifying the terminology.
@@timbrackett1518 - It’s not incorrect terminology. It is just a way of looking at it. “Polarity” is incorrect terminology when speaking of AC, in my opinion. That is a DC term. For AC, we say “opposite phase” instead of “opposite polarity.”
@@GH-oi2jf Sorry the terminology is incorrect. You go look up definitions for phase and polarity. Then come back and tell me again they are the same. They are not! No one cares about your opinion. You come here just to argue? I commented because this “educational video” uses misleading terminology. You commented to argue.
@@GH-oi2jf Phase is a shift of sine wave form. It is not just "opposite polarity". To have real 180 degrees out of phase you would need one sets of wires coming from N-L2 to be longer than wires from N-L1 (or other way around). And because we are talking about 60Hz grid then difference in length should be around half of the wavelength of it. It means: *λ = v/f = (c * VoP)/f*
(.82 * 300000km/s) / 60Hz = 4100km = 2548 miles. Half of it is 1273.81 miles.
I bet you that you usually don't have that much of wiring in an average house.
--------
*λ* wavelength
*v* speed of wave propagation
*f* frequency
*c* speed of light in vaccum
*VoP* velocity of propagation expressed in %. For typical copper wires it's something between 80 to 90% of c.
Awesome explanation! Thank you !
Very good explanation. How would 240 volt single phase 50 amp outlet be wired from the 3 phase?
It would only be coming from one of the 3 phases after a step down transformer at the hydro pole. The single phase is a SPLIT phase of only one leg of a 3 phase system. One waveform is negative, the other is positive at 180 degrees apart... You can see this in every residential area with visible hydro poles. You will see 1 transformer tied in to one of the 3 wires above to serve residential dwellings... When you see a cluster of 3 transformers close together, that's your 3 phase that is going to be feeding a commercial business/factory.
I wired two 240v outlet from the same panel, same breakers and one is 240v and the other 208v?????
👍 great explanation
I understand 208 I'm trying to find out how to get to277
For my 480 volt 3-phase motor I am trying to build a rotary phase converter
In understanding RMS it would be helpful to know what RMS stands for.
Thanks.
Root Mean Square
Thanks.
Thank you for the great explanation
Welcome
Answered my question. Thanks!
Welcome
High-leg delta is a bad system. Symmetrical load is almost impossible. Here in Europe, every household gets 230/400V three-phase power. 230V 1p for normal appliances and 400V 3p for every device above 4kW.
208 uh-oh watch out for the crazy leg.
Great Explanation.
So the 240vac single phase is NOT split-phase. the 60hz waveform does not split. What is happening is the transformer is made to output 240vac and is completely electrically isolated from the input or any other line. then a tap is made in the middle of the winding, like on a welder transformer that has multiple taps. We call that tap neutral and because it is in the middle of the winding it gives 120vac from neutral to each line. So the graph showing two separate waves 180 degrees apart from each other is wrong. it's a single wave form of 240vac.
"Neutral" means connected to ground. The center tap of the secondary is grounded, as is the common line of the wye distribution line. The primary and secondary are not completely electrically isooated because the neutrals are connected.
Can I connect a 208V-1 Phase device to a 120/240V system?
Great explanation, thanks!
Welcome!
The line voltage at the pole is “distribution” not transmission.
Correct, minor misquote, I don't script
So it seems by looking at the comments everyone else is understanding and I am just confused 😡what formula did you use for single phase 180 degrees out of phase when you got 240??? I don’t see how you add there? I thought they were both IN PHASE and then you add 120+120 , you get 240. If they are really out of phase then it’d be called 2 phase no? Basically the question I’ve been searching for my whole career and i can’t seem to find anyone who can explain it in a way I understand .I’ve already spent two hours tonight researching again . My question has been : why is it called single phase when there are two wires that according to you are out of phase. If they were in phase then calling it single phase would make a lot of sense
Please help lol 🥺🥺🥺
Think of it like taps on a transformer..its the potential difference between different points one 240 v coil. The 180 degrees out of phase makes no sense.
hi at-man
please record one clip
about complete axis motor repair and amp adjust
gain setting and balance setting
also clock card adjustment
and
powersupply check
thx a lot 🙋
That is on the list!
Transformers usually don’t hang on telephone poles, they are power poles…
Correct. I learned that long ago from a friend whose dad worked for the power company.
Can 120/ 208v 3 phase generator power a 230v 1 phase welder without modification has 4 prong 120/208v 20amp receptacle beside getting an adpator from 3 prong welder plug to 4 prong from generator?
Excellent thank you
This really helped me understand what’s going on with the 3 phase vs single phase! Is there a way to take the 3 phase 208 any get single phase 220?
With a buck boost transformer.
that was a good long answer, thanks
LOL, I tend to talk ;) Thank you!
I have an electronic dimming switch. It's powered by an L14-20 Plug. The device itself is a 120v device - Half of of the circuits its providing is powered by a 20AMP leg, as is the other. This is context so you don't say the following is absurd and dangerous. Often times, because the L14-20 is not accessible, I use a reverse Y-Splitter (x2 Male Edisons, combined into one female L14-20 Connector). I plug the x2 male edisons into two breakers, knowing they are on different breakers and PHASES. My question: Is there any disadvantage to plugging the two edisons onto different breakers, but the same phase? The advantage is accessibility.
If you plug them into the same phase you can over load the neutral line. For example, if both hot legs are in phase but on separate 20 amp breakers, you will be able to draw a total of 40 amps. Because there in phase the current will sum at the neutral and 40 amps will be on the neutral. Assuming you used the same size wire for all connections it will overload the neutral. When there on separate phases and each hot leg is carrying 20 amps then the neutral current in an ideal system would be zero.
I understand, now. Thank you so much!@@AtManUnlimitedMachining
I really hope someone answers my question: You supply 2 hots to the equipment, but there are 3 wires.. what do you do with the 3rd?
The third wire is the neutral (or it could be a ground). If you have 240V equipment only, you don't need the neutral. But some 240V equipment contains some 120V components. In that case, you need the neutral.
Breh ur amazing
very good.
At 7:50, you mentioned that for 120v, three phase system, a one leg would be higher than 120v and needs to be stepped down. Could you please clarify? My understanding is that the 208v came from 120v with three phases , each phase is 120 degree apart. The line to neutral would be 120v. Thank you.
He didn’t say that. He said if you had 220V 3-phase, the voltage phase-to-neutral would be too high, much more than 120. You want to have 120V service, so that requires that for 3-phase, the phase-to-phase voltage will be 208V.
Again..thank u sir!!!
Your Welcome
my question folks: what's the RMS voltage when utilizing 3 hot legs? (when each is 208v RMS leg-to-leg and each is 120v RMS leg-to-neutral?)
Not sure what your asking, they measure leg to neutral (120) and leg to leg (208)
@@AtManUnlimitedMachininggreat video! still have one question. 240v 3 phase system, If you are reading 208v from leg to leg, and 120v from leg to neutral, can you still read 240v ?
That does not have a straight forward answer. If you have a 208, Y connected service, there will be 120 leg to neutral. There is a service called a "high leg Delta" in which you get 240V leg to leg and its connected in a delta. They then add a center tap to one of the windings on the transformer to provide 120. This configuration has a major drawback of phase imbalance issues. The 120V loads can only be on one phase of the 3 phase system. With a 208/120 Y connection you can balance the 120 loads on all 3 phases.
So if one phase is 180 degrees out of phase with the other, wouldn’t the peak of one and the trough of the other add to 0?
In relation to neutral yes. Not in relation to each other. To measure to eachother, the calculation is subtractive, since voltage is potential *difference.* -120-120=-240.
Great video! A follow up, are all modern 3-phase systems 208V? That is, if I got a 3 phase connect to support an EV Charger would my home now be more like a commercial property where the 240V dryer seems slow?
The utilities like to install 208 3 phase for light commercial applications. It depends on your provider, but I don't think they are installing to many 240 3 phase services new anymore.
Thank you sir
Welcome
Most Informative - Thank you. Clarification question: From the description you gave, I would have thought that in the demonstration (reference 4:24 to 4:30 in the video ) that it would have been +180V then -180V (or more precisely +169.71V then -169.71V) versus the used reference of +120 then -120 {if measuring actual voltage} OR if you are measuring Vrms - then the reference to rms was simply left off in the video during those seconds and thus the 120V was actually 120Vrms??? Can you please clarify? Thank you kindly.
If I remember I think I did the whole video in terms of RMS. I should make a video on the difference between RMS and peak.
THANK YOU!
welcome
Great video. Can you tell me how to wire a high bay metal halide fixture (120v,208v,240v,277v) to a.. I think a split phase (2 hots at 120v each and a physical ground)? I have not been able to get it to turn on it just buzzes. I wired a 277v to a hot, a common to the other hot and the physical ground green. Any help is greatly appreciated
Without looking at the ballast connection it is hard to help.
I have a 240 volt that has 3 wires. A black, a white and a ground. I want to run a 120 volt from this. The 120 volt has a white a black and a ground as well. How do I do this?
Get a single phase step-down transformer, with a KVA rating appropriate for your application. Configure it for 240V on the primary, and 120V on the secondary.
You probably are located in a country where the mains voltage is 240V to neutral and 415V phase-to-phase, and they don't even supply 120V to the typical customer.
Hello guys, so how I can make outlet for 208v?
How do two combined sine waves for 120 volts become one sine wave for 240 volts? Thanks
They don’t. Nowhere in an electrical system do you combine 120v lines. 120v lines come from splitting a single phase 240v service or from one leg of a 3 phase 208v service.
Yeah, didn't answer my question. So how come when I attache oscilloscope to 120 volts I will see one sine wave, when I attache scope to 240 volts I will see one sine wave. Is the scope stupid it doesn't see two sine waves? Thanks
Because the explanation is inaccurate. Spitting 240 doesn’t create 2 phases out of 1 as was implied. If you measure from the neutral to each leg you are measuring 2 different polarities as you have changed the order of the leads.
Kindly explain why, WITH NO OPEN NEUTRAL, some current (unbalanced portion) does travel back to the center tap AND also some VOLTAGE must
move it. I have NO SHOCK when touching the GUY wire outside of the property, going to the transformer? Thank you.
The neutral is referenced to ground. If your grounded and measure the neutral there should be no voltage difference. However, if you disconnect the neutral from a load and measure the loads neutral terminal you WILL get voltage because your completing the path to ground. This is why we use a 3 wire system with an independent ground wire and the Neutral and ground is only tied at one point in the main panel.
At-Man Unlimited Machining Wonderful explanation of KVL Kirchhoff's voltage
law. Open the neutral at a load, measure for voltage, your meter BECOMES
AN ADDITIONAL LOAD. thank you.
Can I connect a Single phase device between two phases of three-phase 208 v system, is it work healthy or a problem will accur.
If it is built for it, yes.
Oh yeah, that graph is wrong too. The graph with 2 “out of phase” 120v sine waves? That graph shows Zero voltage. Since when does 120v plus -120v equal 240v? You keep saying “add two 120v legs”. Nowhere ever are two 120v lines tied together to make 240v. 240v is split. You didn’t shift anything in time. Both haves are still in phase. You are just measuring each side from the middle. In doing so you are reversing the order of the leads on one side compared to the original 240v.
subtract
The graphs are in reference to the neutral and it is a correct example. This is exactly how we measure 240 volts. If you graphed it using “A” phase as your reference, you’d have two sine waves. One twice as big as the other, and they would be in phase with peaks at the same points. You would still measure 120 and 240 RMS.
So I have a question. I am in Taiwan, and my house/shop has a 3 phase supply. When I measure across any of the phases, I get 235 volts. However all 120v appliance is running through a transformer. What kind of system is this? Why is the transformer necessary, and why can't I just take one of the legs and run the neutral to ground?
Because you have 235VAC from phase to phase, even if your connection was a WYE you would get 136VAC from phase to neutral. The transformer steps the phase voltage down from 235 to 120 for you.
@@AtManUnlimitedMachining So 220v appliances are more forgiving of voltage variations? As in 135v is going to burn stuff while for 220v counterpart it's not as critical? Because standard 220v appliance works fine connecting between phases but 110v doesn't. It seems like a weird system to require a transformer to get 110. In a 2 phase system in Taiwan when I measured across 220 I get 250v. Do they have different power plants putting out 1 phase vs 3 phase systems, because it seems the waveform is different, or how do they split it at the substation? My understanding is electricity comes out of a power plant as 3 phase...
@@taiwanluthiers It's not different power plants putting out the different systems. It is the topology of the service transformer. Three phase comes from three magnetic couplings in the transformer between the utility's feeder, and the secondary they give to you to connect your service conductors. Single phase comes from just one of the phases on the utility's feeder, a single magnetic coupling in the transformer, and if it is a split phase system, they center-tap it to make two lines with equal and opposite voltage-to-neutral.
Grid voltage also is a moving target, and it is a challenge for utilities to maintain a stable nominal voltage at your service. When a lot of load is present in your neighborhood, the voltage drops. When load diminishes, voltage rises. There are taps on the transformers that allow for moderate adjustments in grid voltage, to adapt to variations as new customers come online and substations are upgraded.
nice video but do you have any one wiring buck and boost transformers e.g. 208 to 240 etc I want to be able to understand the wiring schematics
Hello Jim, transformers are pretty straight forward, a primary and a secondary. From there the name plate and mfgr info will tell you how to wire it depending on your incoming voltage and your desired output voltage.
I have a 3 phase 30 amp requirement for a water distiller but my house is the typical us single not a 3 phase. Can I still hook up machine by using three 30 amp single breakers or two doubles?
Most likely not. You need to check with the equipment mfgr and see if it can be reconfigured to run on single phase power.
can a 208v heater run with 240v supply?
Most likely not, check the Mfgr specs, I would not operate outside those.
Can i used two phase for lighting or not
Can i used two phase for lighting or not
Hi! Why both peak at same time can measure 240? If they peak together there isn’t voltage potential difference between two leg still can measure voltage? I don’t get that, please explain thanks
I have a Geogebra resource that answers this:
www.geogebra.org/m/qsz3twyg
The black wave indicates the voltage vs time waveform on line 1 (the black conductor) to neutral.
The red wave indicates the voltage vs time waveform on line 2 (the red conductor) to neutral.
The burgundy wave indicates black minus red, which is the voltage across the two line conductors.
At any given time Burgundy Voltage = black Voltage minus red Voltage.
It's not the voltage to ground that you measure black-to-red. It's the inter-phase voltage, that the burgundy waveform measures
You need to subtract instead of add. Voltage is the potential difference.
480v high leg system?
In theory, it could exist, where it is 480V phase-to-phase, and 240V phase-to-neutral on phases A and C. This would make the B-phase high leg 416 Volts to neutral. However, there is simply no application of such a grid.
The delta topologies on a 480V system are usually either corner-grounded delta, or ungrounded delta.
If you have a generator putting out 480v going to a transformer that says 277/480 Y on it, does that mean its stepping it down to 277? Or is that the rated input voltage to the transformer?
A transformer labeled 277/480 Y will have a neutral point. If you measure voltage between two of the hot legs you will get 480V, if you measure the voltage from one hot leg to the neutral leg you will get 277V. You will find a lot of commercial lighting uses 277V so they can run on one leg of 480 without the need for another transformer.
I want to wire a 240 3 phase machine to a 208 3-phase service do I just need to find the two lower legs?
You most likely need a transformer
In europe all have 3 phases 240 and some has 400 volts split fase with a neutral to get both. Only 120 degrees phases here