Why is residential wiring known as single phase?

[pfalcon]

At what electrical engineering universities is it being taught that waveforms being "in phase" are defined by coincident zero-crossings with no consideration of the slope at the zero-crossing?

At most universities. After they finish laughing at you for getting your leads backwards. Then they'll have you adjust your gains until you can see the waveforms are identical.

 

[pfalcon]

Internal to the scope you do.

The phase inversion is a result of how you chose to amplify the signals. It will require a scope with at least one channel with differential capability. Or a switch on one channel that inverts that channel's signal.

No you don't. No it isn't. Phase of a circuit is independent of how YOU decide to look at it.

Outside of this forum I have never heard anyone try to define a signal that is 180 deg out of phase with another signal as being in phase with that reference signal. To do so creates an unnecessary ambiguity, and has no good logical basis.

Because as Mivey said in an earlier post: There is no compelling need to be technically correct.

 

[pfalcon]

V_an and V_bn are in anti-phase with reference to the neutral.
It makes complete sense to use the neutral as the reference. It is, after all, THE common point of a 120-0-120 system.
To get the two 120V sources to appear to be in phase, you'd have to use two different reference points. For me, that seems a bit perverse. But isn't that what you're suggesting?

For practical purposes when there is no compelling need to be technically correct then observing the circuit with N as a reference makes complete sense.

Two reference points are NOT required to see them in phase. Reference on either A or B.

 

[pfalcon]

If one defines V1n and V2n relative to N, then they ARE out of phase by 180 degrees; they do not just appear to be so!/QUOTE]

No. Actually they just appear to be so. They are what they are regardless of what you define or observe. In point of fact they aren't simply in-phase they are actually just the top and bottom half of the same phase. This is classic voltage division.

 

[pfalcon]

Whenever we discuss phase angles, we know that the ideal case (or the fundamental) is assumed. There is no need to qualify things further.

Then you should already understand that ideal cases often have characteristics that are observable but not generally true.

 

[pfalcon]

Whatever I, you, or anyone else defines as the reference matters not a jot.
They work despite any logical or illogical choice anyone makes about what point to call the reference.
But, common sense suggests that the common point is chosen for measurements.
If you want to ignore that and pick a different point, fine.

So use common sense and pick A as a reference so you can see they're the same phase with N as a voltage divider.

Good........
You accept that it is absolutely the case that V_an and V_bn are mutually displaced by 180 degrees.
Do you then accept that using the one and only common point, the neutral as the logical and obvious choice as a common reference?
If not, why not?

I accept neither as stated above.

If you have a compelling need to be technically correct about the phasing then use point A or point B as the reference to make your observation. If you don't then quit worrying about this.

 

[pfalcon]

Fine.
Cite any absolute statement I made that is absolutely wrong.
Be succinct and direct.

Sure. My dryer has both 120V and 240V circuits. Their only common point is A not N. Using N as the reference doesn't make any sense whatsoever. But you keep telling me it's absolutely, positively the only common point and absolutely, positively the only point that makes sense. Yet in my dryer A make sense where N does not.

 

[handy10]

phase angles

phase angles

I am not sure anyone is still reading this thread which is being woven into something like the hair removed from a shower drain. But if anyone is reading, let me air my understanding of phase angle. For sin waves, sin(t) and sin(t-alpha) are said to be out of phase by angle alpha. In three phase, there are three sin functions that are each out of phase by 60 degrees. I assume this is not controversial. If we have a normal residential wiring situation, there are two sin waves which are out of phase by 180 degrees. Why do we need to argue about whether this is called single phase or two phase? There certainly are some reasons for either name, but I doubt many of us are confused about what is meant if either term is used. Can we have a truce?

 

[rattus]

If one defines V1n and V2n relative to N, then they ARE out of phase by 180 degrees; they do not just appear to be so!/QUOTE]

No. Actually they just appear to be so. They are what they are regardless of what you define or observe. In point of fact they aren't simply in-phase they are actually just the top and bottom half of the same phase. This is classic voltage division.

No one is saying there are two phases. We are discussing phase angles, namely he phase angles of V1n and V2n. V1n and V2n are defined relative to N. Since they are defined relative to N, we must measure them relative to N. Then there appears to be 180 degrees separation, therefore there is. If we define the voltages differently as Jim Dungar is wont to do, then there is 0 degrees separation. V1n and V2n are separate entities; there is no reason to

It doesn't matter that these voltages are obtained from a center tapped winding. They could be from separate transformers or generators. Don't be hung up on this common source notion. V1n and V2n are separate entities and should be treated as such.

 

[kwired]

I am not sure anyone is still reading this thread which is being woven into something like the hair removed from a shower drain. But if anyone is reading, let me air my understanding of phase angle. For sin waves, sin(t) and sin(t-alpha) are said to be out of phase by angle alpha. In three phase, there are three sin functions that are each out of phase by 60 degrees. I assume this is not controversial. If we have a normal residential wiring situation, there are two sin waves which are out of phase by 180 degrees. Why do we need to argue about whether this is called single phase or two phase? There certainly are some reasons for either name, but I doubt many of us are confused about what is meant if either term is used. Can we have a truce?

I have no response other than be ready for at least 25 posts of why you are wrong:happyyes:

We are past 1/2 way to 600 posts.

 

[jim dungar]

If we have a normal residential wiring situation, there are two sin waves which are out of phase by 180 degrees.

This is the core of the problem, this is not an absolute statement.
The 180? shift only appears when the neutral is used as the voltage reference point. Choose any of the other possible references all of a sudden the shift disappears.
Ranges and dryers are commonly used in residences, do they use the neutral as the common current carrying conductor for all of their 'internal' loads?

 

[__dan]

Word for the day is ...

Epistemology

The study of how knowledge is acquired. How do we know what we know.

http://en.wikipedia.org/wiki/Epistemology

 

[rattus]

I am not sure anyone is still reading this thread which is being woven into something like the hair removed from a shower drain. But if anyone is reading, let me air my understanding of phase angle. For sin waves, sin(t) and sin(t-alpha) are said to be out of phase by angle alpha. In three phase, there are three sin functions that are each out of phase by 60 degrees. I assume this is not controversial. If we have a normal residential wiring situation, there are two sin waves which are out of phase by 180 degrees. Why do we need to argue about whether this is called single phase or two phase? There certainly are some reasons for either name, but I doubt many of us are confused about what is meant if either term is used. Can we have a truce?

Handy,

We are still talking single phase, but two phase angles.

The separation between phases in a 3-phase system is 120 degrees. This is necessary in order for the 3-phase phasor diagram (delta) to close.

 

[T.M.Haja Sahib]

No one is saying there are two phases. We are discussing phase angles, namely he phase angles of V1n and V2n. V1n and V2n are defined relative to N. Since they are defined relative to N, we must measure them relative to N. Then there appears to be 180 degrees separation, therefore there is. If we define the voltages differently as Jim Dungar is wont to do, then there is 0 degrees separation. V1n and V2n are separate entities; there is no reason to

It doesn't matter that these voltages are obtained from a center tapped winding. They could be from separate transformers or generators. Don't be hung up on this common source notion. V1n and V2n are separate entities and should be treated as such.

Sure,if sinusoid V1n exists,Vn1 also exists.Not with same values simultaneously,but with same value at different instants of time.Same is true for V1n and V2n.
V1n and Vn2 do have same values at different instants of time.They are acting simultaneously on the two loads of the secondary.That is why it is called single phase system.

 

[mivey]

Notice that the same thing happens with two batteries in series, which is an appeal to logic, a broad, true, and useful description. The usefulness of the description makes it science. If the description does not convey understanding, it fails the test of usefulness.

Well sir, the battery comparison fails because there is no direction reversal in a series battery array. You will not get a different phase like you do with an AC waveform. I have posted a graphic on this before but don't feel like looking for it at the moment. But you are knowledgeable enough to graph it out for yourself.

Look at the battery waveform vs the AC waveform and you will note that the battery voltages are always in the same relative position while the AC waveforms alternate position. That physical property is what makes the opposing phase available, not that you have to use it like that.

At most universities. After they finish laughing at you for getting your leads backwards. Then they'll have you adjust your gains until you can see the waveforms are identical.

Not true at all. The voltages can be used either way. Both are valid and depend on the circuit.

I'm more focused on how the voltages are used, not how they are derived as they can be derived in a miriad of ways. What becomes important is that the waveforms are what they are. All the talk about the "windings in phase" with each other and name-dropping polarity-marking standards is just dragging in a different topic to try to enhance a viewpoint. The problem is, the polarity is not the same as the voltage direction and is a separate, but related, issue.

There is nothing wrong with using polarity marking or terminal labels as a reference, but they are related to instantaneous relationships and that is a separate issue from positive voltage direction.

Phase of a circuit is independent of how YOU decide to look at it.

The label may be set by convention, but what is actually there is not independent of how the voltages are used. Keep in mind that the meter/scope is just a load. Using the voltages in one way shows in-phase voltages while using them another way shows two phase-opposed voltages. The meter is not lying to you because it simply shows what is really there.

Both options are available but they are produced by a single device. You would get the same results if the voltages were produced by two phase-opposed sources. That is why I say the configuration of the source does not always define what you take from the cource. Many times the source is capable of delivering more than one output option.

Sure. My dryer has both 120V and 240V circuits. Their only common point is A not N. Using N as the reference doesn't make any sense whatsoever. But you keep telling me it's absolutely, positively the only common point and absolutely, positively the only point that makes sense. Yet in my dryer A make sense where N does not.

It is not the only point that makes sense, but it is probably the most common in the world. The grounded conductor is tied to what is essentially the world's most common reference: Earth. Power quality meters also use this as the reference instead of trying to use two difference reference points (not that there is anything "wrong" with two reference points).

No one is saying there are two phases. We are discussing phase angles, namely he phase angles of V1n and V2n.

I guess that would depend on your definition of phase. While we might not all be able to agree on a definiton, we should be able to agree that there are indeed two equal-magnitude real voltages available as in-phase sources or phase-opposed sources. In fact, that is simply a physical reality.

The labeling and naming conventions really should be the only ambiguity.

 

[Besoeker]

Please do not try to mislead,The center tapped transformer in your post # 288 is entirely different from the center tapped transformer under discussion here in that your transformer secondary windings were wound in the opposite direction,one clockwise and the other anticlockwise so that 180 degree shift is possible.

With respect, that's just plain wrong.
It is a continuous winding with a start a centre-tap and a finish.

 

[mivey]

This is the core of the problem, this is not an absolute statement.
The 180? shift only appears when the neutral is used as the voltage reference point. Choose any of the other possible references all of a sudden the shift disappears.
Ranges and dryers are commonly used in residences, do they use the neutral as the common current carrying conductor for all of their 'internal' loads?

That is correct. Depending on how you use the voltages, you can use two voltages with a 0? displacement, or two voltages with a 180? displacement. The source is capable of supplying both.

 

[Besoeker]

This is the core of the problem, this is not an absolute statement.
The 180? shift only appears when the neutral is used as the voltage reference point. Choose any of the other possible references all of a sudden the shift disappears.

But if you take any other point as a common reference, you won't measure 120V to each of the other two points.

 

[mivey]

They are acting simultaneously on the two loads of the secondary.That is why it is called single phase system.

They do not "act simutaneously" in Besoeker's circuit but are operating like two voltages with a 180? displacement. In fact, Besoeker designed it to operate that way and his circuit requires two phase-opposed voltages. It really is just that simple.

I think the reason many are not understanding is that they can't seem to take their focus off of how the voltages were derived and what things look like up-stream. What really matters is the voltages we have on hand and how we are using them. We can label the source however we want, and these labels are usually set by convention.

Trying to use labels as a definition of a system of voltages, or dragging in some remotely-related polarity and/or terminal labeling scheme just does not fully address the issue.

 

[mivey]

But if you take any other point as a common reference, you won't measure 120V to each of the other two points.

It is odd how some take issue with moving one lead to measure a 180? voltage set, but have no problems moving two leads to measure the 0? voltage set. And for the players on the other team: both voltage sets are valid, real, and available voltage sets.