# 120v /240v residential 180° out of phase



## guitarboyled

Back to basics, 

For standard residential service I understand that both lines are 180 degrees out of phase and this is why we can get a difference in potential of 240v when both lines are used. 

120v + (-120v) = 240v.

But what device creates the out of phase and where is it located?


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## RePhase277

guitarboyled said:


> Back to basics,
> 
> For standard residential service I understand that both lines are 180 degrees out of phase and this is why we can get a difference in potential of 240v when both lines are used.
> 
> 120v + (-120v) = 240v.
> 
> But what device creates the out of phase and where is it located?


In this case, the 180 degree shift is nothing magical. It is simply polarity. It means that the ends of the coil are equal and opposite at any instant of time. In this exact same sense, the poles of a battery are "180 degrees" opposite. North and south are "180 degrees" opposite. In other words, somebody used the term 180, and it happens to have the same phrasing as the 120 degree shift used in 3-phase terminology, except it really doesn't mean a phase difference any more than north or south are out of phase.

The device that creates it is the transformer. At any instant of time, current is flowing in one direction, and therefore the magnetic lines of flux have a specific polarity, driving a current in the secondary a certain direction, creating a positive potential on one side and negative on the other. In the next part of the cycle, the polarity changes, so negative becomes positive and positive becomes negative.

In other words, at any instant, one wire is positive and one wire is negative, thus the idea that they are "180 degrees out of phase".


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## Loose Neutral

I believe the source of the phase difference comes from the generator producing the electricity. I don't remember the exact terms but taking a stab. I think the 2 magnetic poles on the generator are mounted 90 degrees apart. If it were three phase they would be mounted 120 degrees apart.


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## steelersman

Loose Neutral said:


> I believe the source of the phase difference comes from the generator producing the electricity. I don't remember the exact terms but taking a stab. I think the 2 magnetic poles on the generator are mounted 90 degrees apart. If it were three phase they would be mounted 120 degrees apart.


I don't think so.......


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## MDShunk

There isn't really any such thing as 180 degrees out of phase. It's just the difference from one hot wire to another. That's just a sine wave. The 120 degrees is when you're talking about the whole consist of 3-phase generation. In the single phase, you don't really have any reference point like you do with the whole 3-phase supply. 

The 120/240 in a house is more like the output of a potentiometer. We can only measure from one end to the midpoint (120V), or one end to the other end (240V) but if the transformer midpoint were shiftable like a pot, we could make that measurement from one endpoint to the middle anything from 1V to 240V.


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## user4818

There have been very long debates about "phase" as it relates to 120/240 derived from a single phase of a wye or delta distribution system. As for my feeble mind, I can't understand how you can have a phase relationship with something derived from only a single phase, but surely better minds will prevail in this discussion.


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## RePhase277

I don't think there is a single phase distribution system. All single phase is derived from one leg and a neutral, or two legs, of a three phase network. Even if the three phase sine waves are 120 degrees apart, the current in just two wires can only flow in one direction at a time. Which means the magnetic poles of any coil attached to those two wires have to be "180 degrees" opposite of each other.


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## MDShunk

InPhase277 said:


> Which means the magnetic poles of any coil attached to those two wires have to be "180 degrees" opposite of each other.


No!! Not 180 degrees out of phase for the same reason that 120/240 is not "2 phase electric".


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## Loose Neutral

steelersman said:


> I don't think so.......



What do you think.......


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## Loose Neutral

MDShunk said:


> There isn't really any such thing as 180 degrees out of phase. It's just the difference from one hot wire to another. That's just a sine wave. The 120 degrees is when you're talking about the whole consist of 3-phase generation. In the single phase, you don't really have any reference point like you do with the whole 3-phase supply.
> 
> The 120/240 in a house is more like the output of a potentiometer. We can only measure from one end to the midpoint (120V), or one end to the other end (240V) but if the transformer midpoint were shiftable like a pot, we could make that measurement from one endpoint to the middle anything from 1V to 240V.



Of course there is a phase difference, put it on an o scope and you can see that. If not your 2 wire circuit would turn in to a phase to phase fault. With them being 180 out we are able to have 240 volt circuits.


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## RePhase277

MDShunk said:


> No!! Not 180 degrees out of phase for the same reason that 120/240 is not "2 phase electric".


That's why I put it in quotes. It is 180 degrees out in the geometric sense, in the same sense that the poles of a battery or magnet are 180 degrees opposite. That is, they are equal and opposite at any instant in time. It is unfortunate terminology that comes from 3-phase systems, and it keeps popping up.

I'm trying to clarify the difference between the electrical degrees that apply to 3-phase circuits, and actual geometric degrees that mean "equal and opposite"


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## MDShunk

Got it. I guess we're saying the same thing in different terms. 

If the supply was actually 180 degrees out of phase, the voltage would be ZERO!


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## MDShunk

Loose Neutral said:


> Of course there is a phase difference, put it on an o scope and you can see that.


Sure, go ahead a post those pictures... all you'll find is a change in amplitude.


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## RePhase277

Loose Neutral said:


> Of course there is a phase difference, put it on an o scope and you can see that. If not your 2 wire circuit would turn in to a phase to phase fault. With them being 180 out we are able to have 240 volt circuits.


But it's not a phase difference. It is a single phase, so the ends of the coil are "in phase", but opposite. Like I said in the other posts, you are mixing terminologies that have phrases that are "homophonic". In other words, saying that the wires in a 3-phase system are 120 electrical degrees "out of phase" has a particular meaning. But saying the wires of a single phase system are "180 degrees out of phase" is meant in a completely different context, even if the terminology is similar.

In the latter usage, your left and right hands are "180 degrees out of phase". Day and night are "180 degrees out of phase". Blue and yellow are "180 degrees out of phase". Do you see what I'm saying here? I know it is hard to grasp, due to the similarity of the wording. These are geometric degrees, not electrical degrees.


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## Loose Neutral

Man that was a fast response. Don't have an o scope handy that was a long time ago in school. But just to clarify your saying that there is not an 180 degree difference between Leg A and Leg B on a single phase service.


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## MDShunk

Loose Neutral said:


> But just to clarify your saying that there is not an 180 degree difference between Leg A and Leg B on a single phase service.


Absolutely not. They are "in phase". (∠ 0 degrees), otherwise they wouldn't add to get 240. Electronics guys might call this "split phase". Google that, if you care to. The secondary of the 120/240 transformer is just like a potentiometer with a fixed wiper... fixed in the middle.


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## steelersman

Loose Neutral said:


> What do you think.......


you were saying that the 2 poles on a generator were mounted 90 degrees apart. I'm saying I don't think so. I'd say if their mounting has anything to do with it I'd say that they are mounted 180 degrees apart since 120/240 is 180 apart from each other. That's all.


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## Loose Neutral

Where's the electrical engineer when you need one. I'm simply saying i think the phase difference is derived from the generator and leg A's sine wave goes up and leg B's goes down. But I could be wrong it has been a while since school.


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## RePhase277

Loose Neutral said:


> Man that was a fast response. Don't have an o scope handy that was a long time ago in school. But just to clarify your saying that there is not an 180 degree difference between Leg A and Leg B on a single phase service.


I don't possess the finesse with words that will make it clear, but let's see...

Single phase is just that: "a single phase". The ends of the coil are opposite in polarity at any instant, so in a geometric sense, they are "180 degrees" opposite. However, because it is a single sine wave, it makes no sense to speak of its opposite peaks as being "out of phase". How can something be out of phase with itself? A single sine wave is, in fact, perfectly "in phase", because any point you pick will have an equal and opposite value.

In 3-phase, you have three separate sine waves, so it is perfectly legitimate to speak of them as being "out of phase", because you are comparing them to each other.


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## heel600

MDShunk said:


> No!! Not 180 degrees out of phase for the same reason that 120/240 is not "2 phase electric".


I thought it was called single phase because 120/240 comes from just one phase, and it's exactly 180 because each phase is wound in opposite directions


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## Loose Neutral

steelersman said:


> you were saying that the 2 poles on a generator were mounted 90 degrees apart. I'm saying I don't think so. I'd say if their mounting has anything to do with it I'd say that they are mounted 180 degrees apart since 120/240 is 180 apart from each other. That's all.





I thought you might have the answer. I remember seeing poles 90 degrees out but like you said they would have to be 180 out. It's been a while. Still love the pic I grin every time I see that dude.


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## MDShunk

heel600 said:


> and it's exactly 180 because each phase is wound in opposite directions


"each phase". You're talking about phases like there's more than one. Get phases out of your head. The residential supply is more properly "split-phase".


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## steelersman

heel600 said:


> I thought it was called single phase because 120/240 comes from just one phase, and it's exactly 180 because each phase is wound in opposite directions


it's a single coil so it can't be wound in opposite directions. A single coil with 2 ends as any coil will have. And each end is your hot leg with the neutral/ground being tied to the center of the coil.


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## RePhase277

heel600 said:


> I thought it was called single phase because 120/240 comes from just one phase, and it's exactly 180 because each phase is wound in opposite directions


sigh....:no:


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## MDShunk

Loose Neutral said:


> I thought you might have the answer. I remember seeing poles 90 degrees out but like you said they would have to be 180 out. It's been a while. Still love the pic I grin every time I see that dude.


It's the same generator supplying everyone... there's no special phase shifting going on. Everyone is supplied from the same 3-phase circuit from the PoCo.


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## Loose Neutral

My head is starting to shift phases. I need some more alcohol. :blink:


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## RePhase277

Loose Neutral said:


> I thought you might have the answer. I remember seeing poles 90 degrees out but like you said they would have to be 180 out. It's been a while. Still love the pic I grin every time I see that dude.


A generator with poles at 90 degrees would shake itself to pieces:laughing:


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## MDShunk

InPhase277 said:


> A generator with poles at 90 degrees would shake itself to pieces:laughing:


It might also start backwards about 50% of the time.


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## steelersman

Loose Neutral said:


> Still love the pic I grin every time I see that dude.


 
Do you think I should use this one instead?


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## Loose Neutral

Damn that's one crazy mo fo. no like the one you got.


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## steelersman

MDShunk said:


> It's the same generator supplying everyone... there's no special phase shifting going on. Everyone is supplied from the same 3-phase circuit from the PoCo.


What I'd like to know if someone can post a diagram or pic of the primary side of these x-formers? Are there 3 coils or just 1 or what?


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## RePhase277

Loose Neutral said:


> My head is starting to shift phases. I need some more alcohol. :blink:


Seriously, get the idea of "phase" out of your mind when thinking of single phase. Think of these examples that I posted previously: Left and right... north and south.... blue and yellow.... up and down... male and female... day and night... positive and negative....

While these things are GEOMETRICALLY 180 degrees opposite, they are not "out of phase". They are perfectly and naturally "in phase".


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## Loose Neutral

It's hard when you do mainly 3 phase work and have 3 hot's and a nuetral. Then on single phase you have 2 hot's and a neutral. I know it's single phase. Just doesn't sound right.


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## steelersman

Loose Neutral said:


> It's hard when you do mainly 3 phase work and have 3 hot's and a nuetral. Then on single phase you have 2 hot's and a neutral. I know it's single phase. Just doesn't sound right.


Well just think with 3 phase you actually have 3 coils on the secondary side of the x-former, but with single phase you only have 1 coil on the secondary side.


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## RePhase277

steelersman said:


> Do you think I should use this one instead?
> 
> View attachment 1487


Looks like Arnold in 'Total Recall':laughing:


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## steelersman

InPhase277 said:


> Looks like Arnold in 'Total Recall':laughing:


huh, now that you mention it I can see a slight resemblance.


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## Loose Neutral

Looks like he got some type of drug problem. He's on something.


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## Loose Neutral

Damn those teeth are rough


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## steelersman

Loose Neutral said:


> Damn those teeth are rough


I know he could use a serious haircut. That alone would greatly help him out!


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## RePhase277

Separated at birth:


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## Loose Neutral

steelersman said:


> I know he could use a serious haircut. That alone would greatly help him out!




That and some shades.


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## steelersman

hahahaha! That's funny as hell.


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## mattsilkwood

InPhase277 said:


> A generator with poles at 90 degrees would shake itself to pieces:laughing:


 no it wont, it will generate two phase power.


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## drsparky

Two phase works just fine, nothing shakes apart.:thumbup1:


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## RePhase277

drsparky said:


> Two phase works just fine, nothing shakes apart.:thumbup1:


A two phase generator has four poles, each at 90 degrees. 

I was joking about a two pole generator at 90 degrees. It would be horribly imbalanced, and would shake violently. It was a joke, haha, just kidding, a funny.


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## drsparky

I get it now, I am not very bright.:stuart:


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## 76nemo

This is the longest standing debate in electrical theory. As Marc stated, I use the term split phase, but look over your head at your nearest can, it's one leg of the system. Query "Battle of the phases" on Holt's site and see how far this goes, many have different opinions.


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## Larry Fine

guitarboyled said:


> But what device creates the out of phase and where is it located?





InPhase277 said:


> The device that creates it is the transformer.


More specifically, it's the center tap of the secondary that 'creates' it. But, just like two batteries in series inside a flashlight, the two halves of the secondary are definitely 'in phase.'

They have to be in phase in order for their voltage to add. If they were genuinely out of phase, their voltages would buck and the line-to-line voltage would be zero.

The only reason we see what we call opposing polarities, and what merely _resembles_ a 180 degree phase shift, is because we're using the center tap as the point of reference.

Hoping that cross-forum linking is permitted, read this.


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## steelersman

Hey Larry. How many coils are there on the primary side of a typical POCO x-former? I'm thinking for most residential applications it's not 3 coils or 3 phase, but just only 2?


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## RePhase277

steelersman said:


> Hey Larry. How many coils are there on the primary side of a typical POCO x-former? I'm thinking for most residential applications it's not 3 coils or 3 phase, but just only 2?


I'm not Larry (but I'm much better looking), but there is only one coil in the primary of a single phase transformer, and one on the secondary. That's why there is only one, or some times two, insulators sticking out of the top.


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## wwilson174

MDShunk said:


> Got it. I guess we're saying the same thing in different terms.
> 
> If the supply was actually 180 degrees out of phase, the voltage would be ZERO!


In any AC circuit the average voltage is actually zero!


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## steelersman

InPhase277 said:


> I'm not Larry (but I'm much better looking), but there is only one coil in the primary of a single phase transformer, and one on the secondary. That's why there is only one, or some times two, insulators sticking out of the top.


Ok. I didn't know if some x-formers might have a 3 phase primary with only a single phase secondary. So is there only 1 coil on the primary side? I understand the secondary just fine, it's the primary I'm just wondering about.


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## steelersman

If it's a single coil, then what do they supply it with? Like is each end of the coil supplied with 2 of the POCO's 3 phase conductors? Or do they just feed one side with a hot conductor and the other end is grounded perhaps?


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## RePhase277

steelersman said:


> If it's a single coil, then what do they supply it with? Like is each end of the coil supplied with 2 of the POCO's 3 phase conductors? Or do they just feed one side with a hot conductor and the other end is grounded perhaps?


Yeah, if it is fed with two of the three phase conductors, the transformer will have two insulators on top. If it is fed with a single phase and neutral, it will have one insulator, and the can itself is the neutral terminal. So just one coil.

While three-phase transformers exist, I have never seen one on top of a pole. It is always just 3 single phase transformers,


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## Larry Fine

steelersman said:


> Hey Larry. How many coils are there on the primary side of a typical POCO x-former?


If you mean a single can, like you see hanging on a pole, just one, and it's usually what we call single-ended; one primary conductor is tied to the primary neutral conductor.

If there are three cans on the pole, it's three 1-ph tansformers, connected wye, just as we would connect a 208Y/120 feeder or load with a neutral connection.

Now, a pad-mounted transformer can be a 1-ph unit, or it can contain three 1-ph units, like the 3-ph transformers (three 1-ph units) we use, just a lot bigger.

They don't use dual-primary transformers like we sometimes do, but most of their residential units have dual secondaries, which can be re-connected with jumpers.

If connected in parallel, we get 120v between the left (usually) and center bushings, and is used in 208Y/120v systems, with all three units connected the same way.

If they connect the secondaries in series, we get 120/240v using all three bushings, with the center bushing again bonded. That's what we get in our homes.

However, if they connect three of those series-connected secondaries in Delta, we get 240v 3-ph. We can either bond one phase (corner-ground) or bond _one_ neutral.

That would give us a high-leg Delta, with the B phase having the higher voltage to neutral. Note: the A-N-C 3-wire 120/240 section is exactly the same as the 1-ph supply.

If you remove one of the Delta's transformers (not the one with the bonded neutral), you have an open Delta. It behaves just like the Delta. but with a bit less efficiency.

The open Delta began as a modification to existing 1-ph services, for new 3-ph motors. The omitted third transformer eliminated the need for a third primary wire.


Sorry I don't have time to go into a detailed explanation. :laughing:


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## Larry Fine

InPhase277 said:


> I'm not Larry (but I'm much better looking) ...


Yeah. Sure, you are. Uh-huh. :001_huh:






To a Tasmanian Devil, maybe!


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## Larry Fine

steelersman said:


> Ok. I didn't know if some x-formers might have a 3 phase primary with only a single phase secondary.


Nope. There'd be no reason to have the other two primaries there. Only electronics could let us make use of three phases for one.



> _So is there only 1 coil on the primary side? I understand the secondary just fine, it's the primary I'm just wondering about._


There's no magic in higher voltages. Their transformers work just like ours do. There's just more turns of wire in theirs.


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## Larry Fine

steelersman said:


> If it's a single coil, then what do they supply it with? Like is each end of the coil supplied with 2 of the POCO's 3 phase conductors? Or do they just feed one side with a hot conductor and the other end is grounded perhaps?


Sometimes, they use line-to-line connections (Delta) and sometimes they use line-to-neutral (Wye). Most modern installations that I see have Wye primaries.

The Delta primaries I usually see are in older industrial neighborhoods, where there's a pair of poles with a platform between them that three cans sit on, side by side (by side ). 

The primaries are strung between the poles on cross-arms, jumpers reach up to the wires, and the secondaries are likewise jumpered to wires below the cans.


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## CFL

Loose Neutral said:


> Where's the electrical engineer when you need one. I'm simply saying i think the phase difference is derived from the generator and leg A's sine wave goes up and leg B's goes down. But I could be wrong it has been a while since school.


 
I hear this excuse alot and I'm sick of it. I never went to school to learn electricity and somehow I learn more about it each day I'm alive. I hear this crap at work and I guess people expect me to believe they are still smarter than me, they've just forgot more than I've ever learned. Just admit you don't have the answer. Sorry, just one of my pet peeves.


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## Larry Fine

Compact, there must be some things you learned (or were at least exposed to) in some school that you've forgotten from lack of need or use.

I agree that field-learned knowledge is valuable, but not everyone here is in the position to use engineering and math in their everyday work.

Sure, he could have said "I don't know" or merely not have posted, but even posting shreds of information and then getting corrected is a method of learning.

And that's why we're al here, right?


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## CFL

Yeah, I know what he meant. I think I have alot of built up frustration from people I deal with. I hear alot of misinformation coming from people who have been "out of school too long". In some cases I think it's better to keep your mouth closed than to tell a less experienced, impressionable apprentice, for example, what you "think is correct". This is off topic so I'll shut up. No hard feelings, please.


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## Loose Neutral

CFL said:


> Yeah, I know what he meant. I think I have alot of built up frustration from people I deal with. I hear alot of misinformation coming from people who have been "out of school too long". In some cases I think it's better to keep your mouth closed than to tell a less experienced, impressionable apprentice, for example, what you "think is correct". This is off topic so I'll shut up. No hard feelings, please.





Sounds like you have issues. Just like Larry said, sometimes you learn things, don't use the info then forget it. Then even re- learn them and forget again. Use it or forget it. Have a drink and chill.


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## lectric_hand6855

Larry Fine said:


> However, if they connect three of those series-connected secondaries in Delta, we get 240v 3-ph. We can either bond one phase (corner-ground) or bond _one_ neutral.
> 
> That would give us a high-leg Delta, with the B phase having the higher voltage to neutral. Note: the A-N-C 3-wire 120/240 section is exactly the same as the 1-ph supply.


So in a 208 3-phase panelboard with the high B-leg, connecting a 208 single phase load between B-phase and neutral is the same as connecting it between phases A and C correct ?


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## RePhase277

lectric_hand6855 said:


> So in a 208 3-phase panelboard with the high B-leg, connecting a 208 single phase load between B-phase and neutral is the same as connecting it between phases A and C correct ?


No. A 120/208 V system doesn't have a high-leg. A 120/240 V three phase system does. So connecting from B to neutral gives you 208 V, but from A to C you have 240 V.


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## zgozvrm

Loose Neutral said:


> Where's the electrical engineer when you need one. I'm simply saying i think the phase difference is derived from the generator and leg A's sine wave goes up and leg B's goes down. But I could be wrong it has been a while since school.


This is where some of the confusion comes in... 
There is no sine wave on leg A. In other words, you can't supply voltage with a single wire. Rather, you can measure a sine wave from leg A to leg B, from leg A to neutral, or from leg B to neutral. Note that when measuring the 120V sine wave of a 120/240 split phase system with an O-Scope, one typically places the ground clip on the neutral and the probe on one leg or the other. When moving the probe from leg A to leg B, this results in swapping the left-to-right order of the probes and, therefore the polarity. This is why people tend to think that the two 120V sine waves are 180 degrees out of phase.

Again, if they were 180 degrees out of phase,
1) that would mean that they would cancel each other out.
2) there would have to be more than one transformer, since you can't create more than one sine wave (or phase) with a single transformer.


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## zgozvrm

InPhase277 said:


> No. A 120/208 V system doesn't have a high-leg. A 120/240 V three phase system does. So connecting from B to neutral gives you 208 V, but from A to C you have 240 V.


A 120/208V system is a 3-phase system with a wye-configured secondary and is more commonly called 208Y. The center of the wye (the common point of all three transformers) is grounded, forcing its potential to 0 volts. Any leg measured to ground (in effect measuring the output of only one of the 3 secondaries) will then result in 120 volts. There are 3 legs, thus 3 ways to obtain 120 volts and, like all 3-phase systems, they are 120 degrees apart. When you measure leg-to-leg in such a system, you are then measuring the total output across 2 of the 3 secondaries. This results in 208V due to their 120 degree phase offset. If they were in phase, you'd get 240V. If they were 180 degrees out of phase, you'd get 0 volts. (FYI, the 208V sine wave will be 30 degrees offset from one of the phases and 150 degrees from the other).

A 120/240V 3-phase system (better known as 240 center-tapped delta), is derived from a delta-connected secondary. In this situation, the center of one of the secondaries (usually, the one opposite, or not connected to, phase B) is grounded. This creates a 120/240 split-phase system on that secondary. Any leg-to-leg tap will measure 240V. 208V can be obtained by measuring (or tapping) from leg B (opposite the center-tapped secondary) to ground. This is because you will be measuring 240V that is 120 degrees out of phase from 120 volts.


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## Peewee0413

*It isnt that hard*

The primary windings induce voltage to the secondary windings , that has a center tap to ground. It is not the generator nor mr. Faraday himself. It is the center tap that gives it the 180 out. If you can't see or comprehend it. Ill explain more with pictures.


Tesla is my bro,..,........


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## ralpha494

You couldn't wait until next Tuesday to make it a reply to a three year old thread?


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## Peewee0413

wwilson174 said:


> In any AC circuit the average voltage is actually zero!


 Note the average voltage in a 120 volt system is a not zero volt .....root mean squared.!


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## SteveO.

Single phase 120/240V does use both ends of the same winding(A and B, for example)and a neutral (N) tapped from the middle of the phase. 240V is measured from A-B and 120V from A-N and B-N. They are 180 degrees out of phase from each other because A-N is half of A-B, at 0 degrees and B-N is half of B-A, which is 180 degrees out of phase(opposite) from A-B. 

Not sure if my explananation makes sense, but I'll draw it out after I get my kids in bed. 




Peewee0413 said:


> Note the average voltage in a 120 volt system is a not zero volt .....root mean squared.!


Yes it is. The average value of a sine wave is zero. The average value of one alternation is 63.7% of the peak value though. A very different value than the RMS (effective) voltage, which is 70.7% of the peak.


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## Peewee0413

My apologies ..the average voltage of a half wave is a percentage of the peak ..the full cycle is 0, as you stated.


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## triden

I did a quick demo to show you guys what is actually happening from a mathematics point of view. Take a look and you can see what happens with in-phase and out of phase voltages.

http://ieeebcit.org/storage/phasedemo.pdf

hopefully its easy enough to follow.

Chris


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## triden

Peewee0413 said:


> My apologies ..the average voltage of a half wave is a percentage of the peak ..the full cycle is 0, as you stated.


The average voltage of a 60 hz AC waveform is 0 because it crosses above and below the axis in equal amplitudes.

A 120 volt AC signal is actually 340 volts peak to peak. Since the current is varying with time, the average power dissipated by the wave cannot be calculated like DC current. This is where RMS comes in. The RMS value is the equivalent DC value of AC voltage that provides the same amount of power. So even though the AC voltage is 340 volts peak to peak, we like to work with the RMS value of 120 volts so we can do standard power/current calculations.


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## Mindtunnel

Not sure if this was mentioned but the anwer is a center tap transformer. Some older homes or apartments in commercial areas still have the phase 120° apart so you'll only get around 208V or so.


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## cwgabbert

Did not mean to comment here. See below.


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## cwgabbert

MDShunk said:


> Absolutely not. They are "in phase". (∠ 0 degrees), otherwise they wouldn't add to get 240. Electronics guys might call this "split phase". Google that, if you care to. The secondary of the 120/240 transformer is just like a potentiometer with a fixed wiper... fixed in the middle.


Maybe a better description would be to say, for single phase a/c circuits the 2 hot leads are in phase but their sinewave cycle is 180 degrees off.
So when one leg is 120v positive the other hot leg is 120v negative.
They maintain that 180° difference in cycle at all times which gives you 240vac between the hot legs.


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## Almost Retired

dude .... they quit talking about in 2018
check the date above each post


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## drsparky

The OP was from 2009


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## backstay

We beat the single phase is single phase horse to a pulp.


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## gpop

If your going to wake a dead post the least you can do is post the correct answer rather than the trick the scope plays on you due to unisolated channels


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## backstay

Here we go.


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