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Can someone explain what “out of phase” is?
From the pole there are two hots and a neutral. One hot goes to one side, another hot to the other side, and, I believe, the neutral is in the middle.
This is something I’ve just never understood, and would love to have a couple of you guys explain this to me. Thanks.
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You know how alternating current is sent to you in a sine waveform? That is, 60 times per second the voltage on a given hot starts at zero volts (relative to the neutral), ramps up to the peak, then ramps down through zero, reversing the current flow, peaks again (in the trough -- or nadir I suppose)), then returns to zero (60 Hz service).
Well, the phase refers to how the sine waves of two current sources relate to each other. 180° out of phase means that when one hot is peaking, the other hot is peaking in the opposite direction. Current flow on the common neutral is zero if the two hot are equally loaded.
I probably messed this up, I just wanted to see if I could explain it... Did I? Anyone care to explain what the RMS measurement of AC voltage is?
*Don't know if I've ever heard of "out of phase" as an issue in homebuilding... certainly in electrical generation, heavy duty electrical loads (power factor and the like) and stereo (sounds like those subwoofer are out of phase).Andrew got it right, but really you need paper and drawings to grasp the meaning.Regarding RMS. You probably wonder why your electric meter doesn't fly all over the place when you're attached to the 60 hertz line: it uses a circuit to average out the signal and give a "smoothed" measurement (RMS is Root Mean Squared, a standardize measure of averaging). (This is why the meter reads garbage when you have it on DC and try to measrue AC.)In house circuits, the one leg is hitting the peak , when the other leg is hitting the trough of the sine wave. Both are just 120V (rms) over the neutral or 0, but they are 240V from each other. (Multiwire circuits, which use a red/black/white to support two 20 Amp circuits use this phenomena, in which the neutral never carries over 20A, even if both the red and black are at 20 each!)BTW, guess what you have when you have 3 lines, each 120 degrees out of phase? 3 phase power! (Which causes inquiring minds to ask why we don't call the standard stuff 2 phase?)
*The typical home is single phase not 2 phase. Think of the line feed as being a center tap transformer. Each side of the tap is at 120 volts potential to the center and 240 volts from line to line. Both sides are the same phase.
*I was going good thom, until you threw me out of phase with the beer tap comment.Gimme me another shot will ya?Blue
*It takes a pair of wires to make a phase. 2 wires = 1 pair. 3 wires = 3 pairs.Alternating Current. Alternating current switches the directionit travels along a wire. But, it doesn't just switch directions backand forth; that would be square wave current. It goes smoothlyfrom a maximum voltage in one direction to zero to a maximum voltage inthe other direction. The nominal voltage is essentially the averagevoltage in each direction. If you were to graph these voltages youwould have a sine wave.Phase. Since it takes a completed circuit to conduct electricity,there must be another wire carrying it back. If the electricity flowin this wire were the exact opposite of the first wire, i.e. the peaksin one wire matched the valleys in the other direction, we have singlephase. We could say one was 180 degrees away from the other. Now we add a third wire. In order to ballance the system, each setof sine waves must be 1/3 different both the others. This is 3 phasepower. Let's call these three wires L1, L2 and L3. The potentialbetween any one of the three possible pairs of these is the system voltage.Essentially all power generated in this country is 3 phase. Singlephase comes from the distribution system. Electricity is transmittedand distributed at high voltages and only reduced at point of use. 3 phase distribution has all three wires. Single phase has only 2of the three, but there are three possible combinations. L1 and L2,L2 and L3, L1 and L3. In distributing power to single pahse usersthe power company tries achieve ballance among these three pairs.Point of Use. When this electricity gets to where someone wants to use it, it needs to be transformed into voltages that areusable and safe. Let's say the distribution voltage is 12,000.For single phase we have a transformer with two wires wound arounda core, but not connected to each other. Our two 12,000 volt wiresare connected to the ends of one of these wires. This is called theprimary side. If the ratio of the lengths of these wires is 50 to1, the other wire, called the secondary side, will then have a voltageof 12,000/50 = 240. Now if we attach a wire to the middle of thesecondary wire the ratio of the primary to each half of the secondary is100 to 1, so each half of the secondary has 120 volts.3 phase requires three transformers or a transformer with three setsof windings. For the sake of visualization lets look at three transformers. Ignore the primary windings. The secondary windings can be connectedtogether in one of two ways. In a triangle, this is called a delta.Or in a Y.In the delta configuration, the primary secondary ratio is such thatthe voltage between any two corners is 240. A wire is attached tothe middle of one of these so that the voltage between it and the two closestcorners is 120. The voltage between it and the third corner is higher. This is often called the stinger or hileg, but forget it.In the Y configuration the primary secondary raito is such that thevoltage between any two arms of the Y is 208. (there are other voltagescommon for commercial uses, such as 480). The voltage between thecenter of the Y and any of the three arms is 120. (120 = 208/ [sq. root3]).So with 3 phase power you have times the power available at the highervoltage, but only 1/3 more available at the lower voltage. You cannottalk about phases of 120, since for all practical purposes it is not phased.
*Thanks for the very informative post Mike!I think there is still more to say regarding the original post's question. (Esentially, are the two 120V legs in 'single phase' power out of phase.)I've looked at "single phase" 240V power on an oscilliscope, and when you put each of the two legs of the secondary in your delta configuration on a seperate trace compared to the secondary center-tap (neutral), you get an rms volatage of 120v for each leg as expected, but the two legs are indeed 180 degrees out of phase in their waveforms.If you draw a sine function, on top of that a negative sine function (start by going down rather than up) and a line through the zero crossings, this represents the three wires that enter your home. The sine and negative sine are the 'hot' legs, and the line thru the middle is the 'neutral'. The distance between the neutral and a peak on either of the hot lines represents 120V rms. The peak-to-peak distance between the hot lines, is twice this, or 240 V rms. The hot lines are 180 degrees out of phase. (A full cycle is 360 degrees, and you would have to move one of these two curves a half cycle (180 degrees) over so that it would line up with the other, or be in phase)When single phase AC is sent to a transformer with a center-tap, what you get out is two circuits (either leg to the center tap) that are indeed 180 degrees out of phase. But it is called "single phase" because it orginated from a single phase source.Now heres a weird question from me:I was at my family's cabin which had very old wiring (still had fuses etc). We were enjoying the evening when a number of lightbulbs got really bright and burned out at the same time, and other circuits turned off. All the fuses were ok. My brother, an electrical engineer, took a light bulb out of one of the lights that were not working, and put it in one that blew. It also glowed bright then burned out. He thought for a couple min and said that the 'ground must be floating'. This puts zero volts on half the cabin's 120V circuits and 240V on the other half! The power company guys showed up, and indeed the neutral wire had corroded off inside the meter box.I didn't occur to me until now, but if our panel was grounded, and the neutral was grounded at the pole (do they do this?) then how could our ground float?
*We use old inner tubes here in MI for our floating needs!You guys have left me in the basment with this thread!Adios!King BlueOverheard my wife telling her best friend:"All men are idiots, and I married their King."
*Nearly all the commerically generated power is produced and transmitted as 3 phase power. The phases are 120 degrees apart. This angle is largely due to how the generator is physically constructed, i.e., 3 sets of windings equally space around a circle (360/3=120). 3 phase systems are usually configured in either a delta (triangle shape) or WYE connected (schematic looks like the letter "Y") systems. Delta systems have 3 wires, one for each of the 3 phases, and a ground, while WYE systems have 4 wires one for each phase, a neutral (center point of the "Y"), and a ground. The neutral in a WYE system is tied to ground at the box much like the neutral you see in a house hold system.Most distribution systems within a commerical building that has 3 phase power, are WYE connected. Most homes are single phase systems. The primary side of the transformer can either be connected to one of the phases and a neutral,or between 2 phases. In either case the system can only see one of the 3 phases. The "out of phase" question you asked about is most likely a misnomer. In a single phase system like a house, it is very difficult to get "out of phase", unless you are playing around with large inductors, and capacitors. What you can do is inadvertently get 220 volts applied to a circuit that was intended to be 110 volts. The secondary side of the transformer feeding most homes, is wired to be center tapped. This center tap is the neutral (white wire) and it is tied to ground at the transformer and at the distribution box. With a center tapped transformer you end up with 2 hot legs, a neutal wire, and a ground. If you measure the voltage across the two hot legs, you will see 220-240 volts. Between one of the hot legs and the center tap (neutral) you see 110-120 volts. If you set up a 2 channel oscilloscope to look at both pairs of hot-legs-to-neutral connections the wave forms would both be in phase and look identical and each would be one half the size of the wave form that appears across the two hot legs. The neutral wire, unlike the ground wire, carries current in a working system. If the neutral ever develops a bad connection, it can cause some rather bizzare behavior, like turning on an appliance can cause the lights to get brighter. The lights would have to be on one side of the center tap and the appliance on the other. If one happens to inadvertenly mix the neutral and the hot in say an outlet, you will either get a dead short, an outlet that has 220 across it or two circuits that are in series across 220 volts.These improper connections might be what some refer to as "out of phase".
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The RMS value is the area under the curve over time. If you find the total area enclosed by the sine wave and the axis over any multiples of .5 cycles and divide by time you will get the RMS value.
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Floating ground.
If you disconnect the neutral from the transformer, you end up putting both legs of 120v in series with each other. It does not make any difference that the point between them is grounded. You do not get 0v on one side and 240v on the other. You get fluctuating voltages depending on the load on each side. If you put 2 120v light bulbs in series at 240v and they are the same wattage, they will not know the difference. But say you put extremely different loads in series say 10 light bulbs on one leg (which would be in parallel) and one on the other, then the voltage on one leg will be high and the other low. I may have this backwards, but I think the single bulb will blow and then the other 10 will go out, but not be burned out. Replace the single and they will all come on until the single blows. Run this through ohm's law to see how it works. Let me know if I got it backwards.
*More challenges,Tell me how general appliance motors work and what all the (five or so...?) wires do...And are they worth saving and making homemade shop toys....Also how would one figure out how to wire one of these puppies that had been laying around.And how do I slow down the blower in my hot air system...its too loud and I think it runs too hard.Electrically anticipating stimulating yak,Jack : )
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Bob,
Are you out of phase or just single phase?
I bet you're sorry you asked, because you got some nice technical answers. What was the concern or problem behind the question?
Homes are normally wired to single phase AC. Out of phase for you might mean power failure - or zero phase. What does phase matter to a homeowner? Not much unless you are a motor or have a home shop full of big ones. If you are a big motor, it matters a lot.
In 60 cycle single-phase current, the motor's (rotor, stator, armature - I forget, pick one) is magnetized every time the current builds from 0 to peak (120) voltage. A complete cycle takes 1/60th of a second. This happens at the top and bottom of the cycle - every 1/120th of a second. Every 1/120th of a second, the motor gets a boost. Think of it at a single cylinder gas engine going "Poka, poka, poka" as the piston delivers a power stroke. Power to the "poka!"
Since the normal motor runs 1800 rpM, the rotor is doing 30 rpS, which translates to 4 "pokas" per revolution. Not enough for big motors. If the armature is 12" dia., any part on the circumference has to turn 9" between pushes.
To do better and provide more efficient power for industrial operations, 3 phase is used. This is basically three single phase AC sources arranged so their wave forms are 1/3 phase apart - much smoother power. Instead of a "one cylinder motor", you now have three. The "poka, poka, poka" is smoothed out. It's considered nice if these waves stay in phase, just as it's nice if your spark plugs fire in sequence when they should, but that is normally the power company's problem.
ToolBear
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By general appliance motors I assume you mean fractional horsepower induction motors that power fans, refrigerators, furnace blowers, and many stationary power tools. Series style motors, like those used in portable power tools like drills have significant differences from constant speed induction motors. Not all induction motors have 5 or so wires coming out of the motor. The minimum is 2 although a 3rd wire (the ground) would improve the safety aspect. Most single speed induction motors above 1/4 hp are reversible and dual voltage. The dual voltage adds at least two wires. If the motor is multi-speed then the wire count goes up as the number of poles increases. Many furnace fan motors are dual speed, some even have 3 or more speeds and proportionally more wires. Add capacitor start and/or run and you got even more.
As to how to connect all that colorful plastic encased copper emanating from that unused perfectly good motor.... well, if you are lucky there is a label on it or it is stamped on the name plate data. Quite often a call to the manufacturer will provide relief. Without knowing the specifics about the motor it would be hard to even do a good guess.
As to your furnace blower motor, if it has the cooling coils for air conditioning, the motor is usually at least a two speed set-up. For cooling the higher speed is used. Perhaps the system runs the the fan on the high speed all the time. Also check the balance of the fan. The one in our previous house was hopelessly unbalanced. It shook the furnace like a bunch of enraged gerbils in an exercise wheel. I rebalanced it and it made a world of difference. No more squeak, rattle, thunk noises.
*Gordon,I'm learning alot on this thread.But you are incorrect in saying that:"If you set up a 2 channel oscilloscope to look at both pairs of hot-legs-to-neutral connections the wave forms would both be in phase and look identical and each would be one half the size of the wave form that appears across the two hot legs." As I mentioned, I have actually done this and they are indeed 180 degrees out of phase. If what you say was true, the voltage between the hot legs (the vertical distance between the two waveforms on the scope) would be zero, as they would both be in phase and both be 120 Vrms from the neutral. Center taps on a transformer give two circuits that are 180deg out of phase. Think about the AC coming out of the transformer - at some point at time the secondary will be at it maximum peak to peak voltage. Lets call it 240V, although this is not what it is actually due to rms averaging.Now at the center-tap at this point in time, the voltage is +120V to one leg, and -120V to the other. As time goes on, these voltages go to zero, and 120th of a second they reverse, so the voltage from the centertap to the first leg is -120V , and the second is +120V. They are 180 degrees out of phase.This is not called two phase power hovever. To get the answer to what two phase power is I called my father who designed capacitors for Sprague, was later a physicist, and now is retired and consults for a hydrogenerating plant to optimize and monitor their systems, as well as other consulting jobs. He remembers when power distribution was first being designed for Niagra Falls. Apparently Westinghouse assumed they got the bid, and planned on running two phase, which is 90 deg. out of phase. Well it turned out that the spec required 3 phase (120deg phase shifts), and Westinghouse got caught with their pants down. An engineer by the name of Scott became fameous because he came up with a way to adapt all the 2 phase transformers to 3 phase with very little added cost. My father then went on to tell me in detail about 6 and 12 phase generating and power transmission systems for very special applications in industry. Think how efficient a 12 phase motor would be in you table saw!!!
*Aha that makes sense. We must have had a fairly large load (oven perhaps?) on one leg, which was essentially a "short" to ground (pulled the floating neutral up to it), so the other leg, with a couple of lights on, now had a neutral that was 240V from its hot leg. I think Gorden explained it the same way below.Now here is what's weird to me:The neutral is connected to ground at the pannel. Assuming the centertap of the transformer at the pole is also grounded a hundred feet away (I have no idea if this is true), wouldn't you get a current through the ground that prevents the 'floating neutral' from floating too far? Perhaps the resistance of the ground/grounding rods is too high (sounds unlikely to me, but I don't know..)
*Hi Jack,Where in the neighborhood are you? I'm 12 miles N of Saranac Lake, in a town caled Vermontville.It could be easy to set your fan up to be variable speed. First you have to tell me how many wires come from the fan. (I trust you don't have AC here.. ;)I have two old furnace fans. They are amazing placed in windows during demolition work. You can even watch chunks of plaster head for the window. Boy do they suck!Rich
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Richard, What happenen to you is a rather common occurance on some of these old meter sockets. The top cable entry holes developed leaks and corroded the neutral connection, thus effectively disconnecting it from any ground. The panel probably wasn't even grounded or the ground was very bad (also very common!
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Richard,
I struggled with and am still struggling with the 180 out-of-phase issue also. Intutively your arguement sounds correct. But I also remember that for the two wave forms to be additive they have to be "in phase". I don't have my old double E texts to look it up, but I do know that if the wave forms are 180 degrees out of phase, that they cancel each other out which is what the active noise suppression systems do. They measure a wave form and construct one that is 180 degrees out of phase and pipe that to speakers or your head phones. The 180 degree out of phase noise cancels the original noise. Also the another thing the bothers me, is that if it was that easy to generate another wave form that was 180 degrees out of phase I would have thought 2 phase motors would be be all over the place. 2 phase is quite possible as is 4, 5, 6... phase equipment. 3 phase apparently is the best overall solution in terms of efficiency and cost.
Obviously more research is in order so I guess I need to find one of the double E's here at work and get him to explain this to me.
Here EE, Here EE, come on out and play, I will give you nice treat if you can explain this to me ;-)
*Richard,I'm in Warren county area...And as for my fan..I have a York heat pump w/ electric backup...6500 kw electric usage for Jan and Feb...The air blowing is the noise I hear...it blows too fast as far as I can tell, though I have no expertise. I think it only runs at one speed and would love for it to have two or three....Just checked wires from motor...(plate 220v 3a, has one way rotation arrow)...capacitor brown and purple and feed..blue to motor..red and black to motor not used...fan is balanced well enough.Will be converting 35kw electric back up section to fuel someday soon.Heat pumps should be illegal north of the Mason-Dixon line.Chillin in Upstate,J
*Jack,Since you have unused wires, it is possible for the motor to be multi-speed. If you have or can get the paper work that came with the York indoor unit (air-handler) you could look up what the unused wires do. Instead of the heat/cool switch switching fan speed, you may just have to swap wires manually at the season changes.Good luck,Frank
*Gordon:They are 180 degrees out of phase and if you connected them together they would cancel out just like the noise cancelling example. However since larger ammounts of power are involved than in noise suppression, expect sparks, high amps and blown fuses/tripped breakers. Go ahead and try this at home, just read and sign this disclaimer in the presence of Andrew d.....FrankYou cannot make things foolproof because fools are so inventive.
*Andrew:RMS is Root Mean Square. If you look at the waveform of AC voltage, you see it sweeps from a peak above 0 volts to a peak below 0 volts. The voltage between peaks can be seen and measured on an oscilloscope. These peak to peak measurments are very often the measurments used to design and service signal circuits. But in power, we are not interested in peak voltage or current, we are interested in power, the ability to do work. Since the time the voltage is at the peak is very short, not much work will be done at peak voltage. The work done(power) will be valued at some average voltage, not peak voltage, and average current, not peak current. These averages are the root mean square. I do not have my EE textbooks before me, but I recall peak voltage=1.41 X RMS voltage. So the 120 volt AC line has peaks of 170 volts.Frank
*"Out of Phase" is also the title of a half-decent Star Trek/Next Generation episode where Geordi and Ensign Ro have their matter "shifted" in phase to invisibility by a Romulan cloaking device and travel around the ship walking through walls but somehow not falling through the floor. They kill a Romulan, similarly cloaked, by throwing him through the side of the ship into the vacuum.Now some nitpicker is going to complain that this is off topic. I might even get deleted by the censor.All in good fun, AD :)
*Hi Gordon,Those active noise supression systems are neat, now if they only will make one that I can hook to the kids from time to time!I think the confusion here is that some of these cases are additive and some subtractive. Two ocean waves that intersect in phase for example are additive, and will create a wave the sum of their peaks in amplitude at their node.However, when you measure voltage with a volt meter, you are measuring a potential difference, so 180 deg out of phase will give the maximum difference at the peak.Frank's example below is additive, connecting the two hot legs together adds their potential, and in this case the potential sum is zero. (Not the current though!) The active noise supression systems are additive as well.I'll ask my father about the 240V motors, but it is my very limited understanding that there is an equally efficient way to design windings such that you don't have to make use of the phase difference. Tee advantage here is twofold:1. You are using 240V single phase rather than 2 120V circuits, so you can use lighter wire as there is half the current (cuts costs).2. You can put a pair of windings in series or parallel so that the motor will run on either 120V or 240V, like most shop tools.I'll find out more about this.Re: Star Treck below, is this thread realted to phasers? I know a bit about lasers and masers, but maybe it was a phaser that him my cabin when the power went wacco?Always out of phase,Rich
*Frank,That's what I'm thinking...or I could just try them with my welding glasses on..Jumpin Jack : )
*Hi Jack,Frank's idea is the best to try first - could be as easy as adding a switch to get two speeds!I'll talk to my father about other options (variable speed). I have some ideas, but he would come up with the most energy efficient. 6500 kw last bill, Ouch! Did you get the flyer from Nimo about variable rate electric? What do you think?Off to shred at Whiteface - FINALLY a powder dump, maybe the rockslides will be covered enough to play in the backcountry?Careful with that heat pump - you might trigger a subterranian ice age up here...Rich
*I agree, the panel must have had a poor ground too. Does anyone here know if the neutral is grounded at the transformer?We finally rewired our cabin, and got a new meter box from the power company. No more fuses!
*R. - The transformers are usually attached to a ground rod. However, a single rod knocked into soil with poor conductivity makes a lousy ground at 240v. Lee
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Regarding the out-of-phase versus different sides of the transformer issue:
Both sides of this issue are actually correct.
The center tap of the transformer on the power pole is tied to neutral. Each hot lead measures 110 volts difference from this center tap and therefore to neutral. However, they measure in the opposite direction. Here is a good analogy. You and your wife are on vacation in Miami(elevation = 0). You are in the lobby of a posh hotel with a shopping boutique on the second floor and a sport's bar in the basement. She takes the elevator and your master card up to the boutique and is now at +30 feet elevation. You mozy down for a brew and some basketball and are now at -30 feet. If you were to add +30 + (-30) you would indeed have zero. This is the concept of sine waves cancel. However, we are taking the difference(subtraction) not adding. This is +30 - (-30) which equals 60. This matches the obvious fact that the physical distance(analogy to voltage) between you and your wife is 60 feet.
Okay, so you can think of one hot leg being at +110 and the other at -110. The difference(voltage also called potential difference) between the two legs is 220. Now, you may remember from trigonometry that -sin(angle) = sin(angle-180). You can draw two sine waves on graph paper and prove it to yourself. That means that two sine waves where one is negative A volts and the other is positive A volts are by this nifty trigonometric law 180 degrees out of phase.
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Story someone told me years ago, hopefully false, that only people like those on this thread could laugh at:
Vandenberg noticed that all of its clocks were running faster than normal. Someone tested the power feed and found that it was running above 60 Hz. They called the power company and were told, yeah, we did that so by the time it gets to you it comes out right.
Relativistically yours...
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Bob, if you provide me your e-mail address I'll send you a couple diagrams that simplify and summarize what these guys are saying. As the old saying goes a picture is worth a 1000 words. The phasing issue is very simple and the Toolbear did a good and funny analogy to a gas engine for you. As a retired double E, I can clarify with a couple of diagrams, However, the real next problem is you probably have a PC and I switched in 1983 to a MAC becsaue of the MAC's superior approach with graphics. Let me know if you are versed in downloading graphical .JPEG files which are cross platform and I'll convert either a Microsoft Powerpoint or Canvas drawing (latter is better) file to .JPEG for you.
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Can someone explain what "out of phase" is?
From the pole there are two hots and a neutral. One hot goes to one side, another hot to the other side, and, I believe, the neutral is in the middle.
This is something I've just never understood, and would love to have a couple of you guys explain this to me. Thanks.