Why is residential wiring known as single phase?

[rattus]

When did I say you cannot choose the reference point you want to use?
The problem seems to be you choosing only parts of the equality: -V2n=Vn2. You have 'an inversion' and 'a rotation', but your analysis seems to only focus on the rotation.

Potential to dirt (ground) means nothing to me except when I am dealing with issues concerning lightning, however potentials to a common reference plane are extremely important to me.

Choosing an 'always' reference is often very in convenient. There a 'single' common in high-leg deltas, zig-zag or T transformer connections either. Corner grounded delta primaries feeding neutral grounded wye secondaries also have two different relations to ground.

Do what you want on paper. I guess you have missed where I said I do this all of the time, but when I do, I apply V2n=-Vn2 in a consistent manner and I understand how my paper analysis relates back to my real world reference.

Jim, you of course will do as you have always done. No one expects you to change that. But when a problem involves the neutral as a reference, you always go back to your way. So why don't you just accept that. No big problem is it since you understand it both ways?

 

[rbalex]

Does anyone think we are making this too complicated?:happyyes:
We need to look at this from a higher level, and understand the real meaning of a ?phase?.
Let?s start without a neutral.
If we reference L1 and look at L2 we have 240V single phase.
If we reference L2 and look at L1 we have 240V single phase.
We don?t have two phases. It?s the same one.

For the same reason if we happen to use the center as out reference, we still only have the one phase, we are just choosing a new reference. Yes, you can make a formula that shows a ?phase relationship? of 180 degrees, but you didn?t change the physics of what is really there.

Otherwise three-phase is really six-phase, and that probably deserves its own thread?

I will bring up my hill analogy. Imagine being at the top of a 240? high hill. If we walk half way down, we still have one hill that we are in the middle of. Not two hills, one up and one down.

While I happen to agree with you - unless you start from or offer a definition of phase; its just our common opinion.

Two of the four principal "two phases in a single-phase system" advocates don't accept any formal definition. One of them quite honorably offered a "personal one" though and simply wants pragmatism to be the ultimate principle. Another accepts the definitions but doesn't like the application, but honourably attempts to find a second-phase within applications - not the definition. Another keeps trying to indiscriminately change definitions or their appropriate application if he happens to stumble on one accidentally.

 

[pfalcon]

A vector doesn't have a different magnitude at the head and the tail.
But your other diagram showed a reference at the head for each vector, and it was also incorrect.
120@0 - (-120@PI) = 0

Respectfully David, A correctly drawn phasor has only magnitude and direction. The magnitude is considered 0 at the tail and |absolute| at the head.

Correctly presuming points A,N,B

@B 0 ------> 120 @N
@N 0 ------> 120 @A

or

@A 0 ------> 120 @N
@N 0 ------> 120 @B

Also when properly drawn phasors are typically additive not arbitrarily subtractive therefore
120@0 + (-120@PI) = 240 NOT 120@0 - (-120@PI) = 0

which if properly drawn would be closer to:

----------> 120@0
<---------- -120@PI

but that violates phasor convention so the second phasor should use the proper identity -120@PI = 120@0 to reduce to

-------> 120
-------> 120

which therefore becomes the conventional phasor addition to 240

 

[david luchini]

Respectfully David, A correctly drawn phasor has only magnitude and direction.

Yes, that is what I said.

The magnitude is considered 0 at the tail and |absolute| at the head.

It's -120 at the tail,

You have just contradicted what you said earlier.

Also when properly drawn phasors are typically additive not arbitrarily subtractive therefore
120@0 + (-120@PI) = 240 NOT 120@0 - (-120@PI) = 0

I would suggest that you take Jim's refresher course on phasors:

In a tail-to-point configuration we ADD the phasors together.
In a tail-to-tail or a point-point configuration we SUBTRACT them.

You drew two phasor diagrams...one tail-to-point and one tail-to-tail.

For the tail-to-point phasors, you would add them: -120V@0 + 120V@0 = 0

For the tail-to-tail phasors, you would subtract them: 120V@0 - (-120V@PI) = 0

In both cases, your phasors combine to zero volts, not 240V.

I notice you did not address the point that your math was wrong.

V_1n = V_m*sin(wt)

V_2n = -V_m*sin(wt+180)

V1n = Vm*sin(wt)

V2n = Vm*sin(wt+ PI)

One of either you or Bob is incorrect in your notation of V2n (hint: it's not Bob.) V2n cannot be both "minus" Vm*sin(wt+ PI) and "plus" Vm*sin(wt+ PI).

If you correct the math error, your phasors would work out fine.

 

[rattus]

Finis

Finis

Suffice it to say:

The two voltages in a split phase system are properly described by:

V1n = Vm*sin(wt), phase is (wt)
V2n = Vm *sin(wt + PI), phase is (wt + PI)

NOT by an inverse! That is chicanery.

If you draw the phasor diagram, the V2n arrow is directed away from the other.

Two different arguments, two different phases!

Until we see some references, we must regard rbalex's argument as unfounded.

I am tired of arguing with a bois d'arc stump. My heart can't take it!

 

[jim dungar]

But when a problem involves the neutral as a reference, you always go back to your way.

The only problem I have with the neutral as a reference, is when the analyst does not acknowledge that for the equality of Vxn=-Vnx, two opposing actions have occurred. First there is the action of the 'rotation' of the subscripts and second the inversion of the first action.

It is exactly for situations like this, that most oscilloscopes have an 'invert waveform' function.

 

[rbalex]

!

Suffice it to say:

The two voltages in a split phase system are properly described by:

V1n = Vm*sin(wt), phase is (wt)
V2n = Vm *sin(wt + PI), phase is (wt + PI)

OR

V1n = Vm*sin(wt), phase is (wt)
V2n = -Vm *sin(wt), phase is (wt)

OR

V1n = -Vm*sin(wt + PI), phase is (wt +PI)
V2n = Vm *sin(wt + PI), phase is (wt +PI)

NOT by an inverse! That is chicanery.

OR

You only learned to manipulate trig identities with very careful instuctions - but never understood what identities are or how to transfer their application outside an instuction book

OR

You still don't understand phase any better than you did in 1956. (Post 1551)

If you draw the phasor diagram, the V2n arrow is directed away from the other. Yes - So?

Two different arguments But phasors don't have arguments - they are graphical representations of rotating vectors. Their representative mathematical expressions may have arguments, but those can be written in several equivalent ways two different phases! False

Until we see some references, we must regard rbalex's argument as unfounded. A competent engineer wouldn't need a reference to how trig identities work. Enough others have told you that.

I am tired of arguing with a bois d'arc stump. My heart can't take it

 

[pfalcon]

Sure I can put the chassis at 1000 V relative to the earth. But for my circuit analysis the chassis is going to be zero as my reference because that makes sense in relation to the vacuum tube circuit I am analyzing. I should have pointed out that ...

And it's obvious you didn't really read my post.

 

[rattus]

The only problem I have with the neutral as a reference, is when the analyst does not acknowledge that for the equality of Vxn=-Vnx, two opposing actions have occurred. First there is the action of the 'rotation' of the subscripts and second the inversion of the first action.

It is exactly for situations like this, that most oscilloscopes have an 'invert waveform' function.

Jim, I don't see any problem there. We all know that is true. But if we use the neutral then we should refer all voltages to it--if possible.

 

[engy]

I am attaching a crude sketch of a vector diagram.
It shows a three phase system and a (arguably) single phase system derived from it.
No matter how you split the single phase system, they have the same vector relationship.
Maybe someone can draw a prettier sketch, or a more articulate explanation... View attachment Phase.pdf

 

[pfalcon]

Why is there such resistance to using the neutral/ground as a reference in the split phase system? It is used in the three phase wye without any objection. ...

There isn't any resistance at all. Unless you're trying to answer the OP question. Then the same objections to your neutral reference happen during your three phase references, they just aren't as refined yet.

Fact: Except at the zero crossing, One end of the secondary is HIGH, the other end LOW.

By the OP question that fact has absolutely nothing to do with why it's called "single phase", the two ends are 180 degrees out of phase but that condition can be created through numerous methods. Hence it's not an actual indicator of whether the system is single phase. I can stack a score of phase-matched transformers to create the same condition. Series ended BCDEFGHIJKLMNOPQRSTUVWXYZ. N is still the neutral, B & Z are still +/- 120V to neutral. But it's now a phase matched system and no longer single-phase but a 24-phase system.

With that 24-phase system Rbalex will still demonstrate that they're all the same phase. But Rick will demonstrate it's not the same phase because the noise doesn't replicate through the entire series. YOU will still point out, correctly and with no actual objections from anyone, that the sine waves generated by treating each end as independant are 180 degrees out of phase.

The word PHASE is overloaded. If you and Rbalex wish to end your differences, forget the math and get a solid fix on which definition of phase you plan to use. Include it in EVERY post you make and argue against that definition. Not a picture from a book or magazine but a dozen clear words.

Single phase is called single phase because it is generated by a single electromagnetic field across the entire secondary coil.
Single phase is all the same phase because it is all of one thing and therefore the pure mathematics of Rbalex MUST support that conclusion.
Single phase is all the same phase and therefore an added noise generator will support Rick's conclusions because it physically cannot do otherwise.
Voltages that are measured WITH the phase must by physical law trace exactly 180 degrees out of phase with voltage measurements taken AGAINST the phase.

But those statements above are from a white room. On the floor where the dirt is:

We measure from ground and call ground zero volts. Current and Voltage have leads and lags to each other. Mathematically we call leads and lags on sine waves "phase shifts". Therefore us adaptable humans working in the dirt have taken to calling those voltage and current readings "Phases". We do and therefore they are. We work from zero volts and therefore don't CARE about the white room definitions. We treat the end voltages as though they were independent voltages. They aren't independent but that actually works in our favor. Circuits we design are actually simpler because we don't have to deal with independent voltages. Whether we measure WITH or AGAINST the phase is not relevant on the floor.

So when someone tells you direction matters, or your leads are backwards: They're speaking from the white room and trying to answer the OP question.
When you say it doesn't matter: You're speaking from the floor and not answering the OP question. But you are answering a question and in that application you are correct.

 

[jim dungar]

But if we use the neutral then we should refer all voltages to it--if possible.

But if we use the transformer winding outputs as the reference, then someone didn't waste their time putting on all of those dots you mentioned earlier. And we can be consistent regardless what transformer based system we are analyzing.

But, I thought we resolved the arbitrary choice of references many posts ago. Haven't the past 1000 or so posts primarily dealt with your handling of the waveform relationship of Vbn=-Vnb?

 

[gar]

120309-1557 EST

Jim:

I don't understand your reason for the scope inverting switch. Thus, I will present my conjecture.

1. Most scopes have the EGC connected to the scope chassis.
2. Most scopes have some part of the power supply for the electronics connected to the chassis.
3. Most scope amplifiers are single-ended, meaning one terminal of the signal input is connected to the chassis.
4. There are some scopes like my Tek 502 (I believe that is the number) that have differential input amplifiers like the 502. Also the 502 has 2 beams as distinguished from dual trace.

A differential amplifier is one that allows measuring the difference in voltage between two points that are both not at the same voltage as the amplifier common (scope chassis).

If a scope has no differential amplifier, has two Y-axis amplifiers, has a switch to sum the two amplifiers, and another switch to invert one channel, then by adding, inverting, and setting both channels to the same gain it is possible with this essentially single-ended system to have the capability of a single channel with differential input capability.

.

 

[rattus]

But if we use the transformer winding outputs as the reference, then someone didn't waste their time putting on all of those dots you mentioned earlier. And we can be consistent regardless what transformer based system we are analyzing.

But, I thought we resolved the arbitrary choice of references many posts ago. Haven't the past 1000 or so posts primarily dealt with your handling of the waveform relationship of Vbn=-Vnb?

No, the argument is about rbalex's claim that V1n and V2n have the same phase.
He cannot produce a reference though which supports that claim.

 

[rattus]

I am attaching a crude sketch of a vector diagram.
It shows a three phase system and a (arguably) single phase system derived from it.
No matter how you split the single phase system, they have the same vector relationship.
Maybe someone can draw a prettier sketch, or a more articulate explanation... View attachment 6589

Thanks Engy,

What you have provided is a phasor diagram of bes's 6-phase system. We know it is provided from a 3-phase source, but according to the definition of phase, there are six phase angles present, therefore he can call it a hexaphase system (from a 3-phase source to satisfy the purists).

It is essentially three split phase systems with a common neutral.

 

[rbalex]

There have been three formal definitions of phase proposed and, when properly applied, they all lead to the same conclusion: however the voltage functions in a conventional 120/240V system are validly determined; they can all be expressed in terms of a common Sine argument - a single phase. The Sine argument is called the phase; e.g., the phase of sin (ωt + φ₀) is ωt + φ_0.

Basically, phase is a mathematical concept that has been applied many ways, in multiple fields of physics, usually through trigonometric expressions. However, some seem to believe it is the various applications that define phase, especially if their particular field uses it in a particular way. What others don't seem to recognize is that if trigonometric expressions apply - trigonometric identities apply as well. That is, sin (ωt + φ₀) is identically equal to -sin (ωt + φ₀ + π) in ANY application. If it isn't, then trigonometry simply doesn't apply either.

The defintitions : Post 1084.

 

[Besoeker]

No - I'm saying it's a glorified three-phase system - what happens down stream is irrelavent.

The 120-0-120 residential service IS downstream.
Exactly in the same way that the hexaphase arrangement is.

 

[rbalex]

The 120-0-120 residential service IS downstream.
Exactly in the same way that the hexaphase arrangement is.

Yes-So? Are you suggesting the service equipment creates the transformer system voltages? So disconnect the service equipment and the transformer voltages are still the same. Of course you can monkey with the transformer connections too, but then we are no longer talking about a conventional 120/240V system, are we?

 

[Besoeker]

Let's let the lab assistant hold onto the positive pulse outputs and see if he thinks it is just math or physics.

Starting around the clock-o-phase, we move 60­?:
Assistant: "Hey, what was that?"
Mr. Resolver: "That was not real positive pulse but was just the inverse of the voltage we would have on the other half of the period. Don't worry about it. I extracted a negative sign to reduced the number of phases."
Assistant: "Errr. OK."

Another 60?:
Assistant: "Ouch"
Mr. Resolver: "Easy, easy. That was a real positive voltage pulse. That's to be expected at this phase."
Assistant: "Well just how many phases are there?"
Mr. Resolver: "There are only three phases."

Another 60?:
Assistant: "Owe. This is getting old. I'm sure glad I'm getting $50 per phase."
Mr. Resolver: "That was another pulse. Some try to call that a positive pulse but we who done learned our Trig know it is really just a negative of a different phase. But I removed the negative."
Assistant: "Well you must not have removed all of it 'cause that hurt. Do you have any references for what you are doing?"
Mr. Resolver: "No. But if you want to question me, I'll need some references from you."

Another 60?:
Assistant: "Hey! What's going on? I thought there were only three phases!"
Mr. Resolver: "True dat! You see, I can make six phases magically become three through trig manipulations."
Assistant: "I think I see my $50 is going to magically disappear too. Do you even know what a phase is?"
Mr. Resolver: "Sure. Your problem is you just don't understand the proper mis-application of math."
Assistant: "But I understand why none of this was in the textbook and why I could not find this in any reference material. I believe I'll leave you to experiment on your own."

Nice job.
:thumbsup:

 

[Besoeker]

Yes-So? Are you suggesting the service equipment creates the transformer system voltages?

Nope.

Of course you can monkey with the transformer connections too, but then we are no longer talking about a conventional 120/240V system, are we?

The hexaphase system in no way monkeys around with the conventional 0.120/240 system.
It is preciously the same arrangement for each of the three phases of the primary that you have with the domestic arrangement.
My point in introducing it was to demonstrate why the number of secondary voltages is not always the same as the number of primary voltages.
You can understand that. You are a professional engineer.