Why is residential wiring known as single phase?

[Rick Christopherson]

So an equivalent circuit for a voltage source that consists of an ideal voltage source and a single equivalent series impedance is more than adequate for many problems. From this I am satisfied that I can get sufficiently good results in analyzing a real normal center tapped secondary power supply by use of two ideal voltage sources and their equivalent series impedances.

I don't disagree. The difference is that you know that this is just a model of the system. These guys can't seem to make that distinction. Because the math model fits the system well, they mistakenly extend that to mean that the math model defines the system, instead of the other way around.

Mivey's mishandling of your sawtooth example makes this quite clear. He has gotten so accustomed and complacent with the application of his trig identity Sin(wt) = -sin(wt+1/2T) that he forgot that it doesn't apply to all periodic functions. He was relying on this identity to be able to claim that an inversion is the same as a phase shift, so instead of drawing a phase shift, he drew an inversion.

 

[jim dungar]

You know of course I was referring to electrical nodes. Don't play word games.

Where is it written that you must use an electical node as your reference?

It seems you put restrictions on things to suit your own needs. I try to be consistent when assigning directions to my phasors. I try not to deviate for my methodology simply because a neutral point exists.

None of these voltages are inverses. sin(wt) and -sin(wt) are inverses. Van and Vbn are inverses.

Again it would help if you read what was actually posted, I did not use the word inverse. I am very confident that setting up my equation as an equality was done properly.

They are all equivalent,....

Are you seriously saying that all definitions of the word 'phase' are equivalent, even if we limit ourselves to a subset of just those applicable to waves?

 

[rattus]

Where is it written that you must use an electical node as your reference?

It seems you put restrictions on things to suit your own needs. I try to be consistent when assigning directions to my phasors. I try not to deviate for my methodology simply because a neutral point exists.


Again it would help if you read what was actually posted, I did not use the word inverse. I am very confident that setting up my equation as an equality was done properly.


Are you seriously saying that all definitions of the word 'phase' are equivalent, even if we limit ourselves to a subset of just those applicable to waves?

I am saying you are not responding to the issue:

Can a sine wave such as [sin(wt)] be 'in phase' or 'of the same phase' as its inverse, [-sin(wt)]??

 

[gar]

120318-1412 EDT

On the subject of the word --- phase :

There are at least two general ways that phase is used in relation to periodic wave studies. These are:

1. As a measurement of position or position difference in a periodic wave in relation to the period. For example the positive peak of a sine wave is displaced by Pi/2 radians from its positive slope zero crossing.

2. As a name of a wave with an appended letter or number to identify different waves. For example the hot wires in a three-phase Y system may be identified as Phase A, Phase B, and Phase C.

In post 1084 three definitions were quoted. These all related to phase used as a measurement.

The first uses angle as the unit of measurement, no indication of the use of a modulus, does not relate to the wave period, and is not clear whether the reference point is always zero.

The second definition includes the period as the modulus, is non-dimensional, and can have an arbitrary reference point. Seems to be specific to time as the independent variable.

The third makes it specific to a periodic function (the second one implied this), and although "t" is used as the independent variable it only implies time and does not require time as the variable. Basically two and three are essentially identical.

We have to assume for all of these definitions that the referenced period is that of the lowest frequency component of the function.

None of these define "same phase", "in-phase", "out-of-phase", "phase difference", "phase angle", or any other kind of modifier attached to phase. The definitions do not prevent the use of Phase A to identify a wire, or wire pair.

My normal usage of the word same as a modifier in combination with an understanding of the meaning of modulo means to me that only phase differences of 0, or +/-N periods could be called the "same phase". This means a phase difference of 0.5 (Pi, 180, or whatever units) is not of the same phase.

.

 

[Besoeker]

Please don't stop there with your magical trig identities.

Go a few more steps.
sin(wt) = [-sin(wt+PI)]

Which also means that:

Vmsin(ωt) ≠ Vmsin(ωt+π)

Thus two waves.

One wave, one phase!

Nope. See above.

 

[rattus]

Whcih is which?

Whcih is which?

I have a dilemma!

We have bus bars, L1 and L2, with voltages V1n and V2n, which happen to be inverses. But which is the 'real' voltage and which is the inverse? How would the installer know? Both wires have black insulation, at least in my area. Would he have to climb the pole and check primary and secondary wiring? Would he have to ascertain which phase of the wye was used? Would he have to consult an IEEE standard?

Maybe he is supposed to, but I'll wager that most are too rushed to do all that and just flip a coin. In that case we must assume that it could be either and treat both V1n and V2n as being of equal importance. They both shock with equal strength. I know, been there and done that.

If V1n and V2n are of opposing phases, then V12 = 240V

If V1n and V2n are of the same phase, V12 = 0.

But that can't be now, can it??

 

[__dan]

I have a dilemma!

We have bus bars, L1 and L2, with voltages V1n and V2n, which happen to be inverses. But which is the 'real' voltage and which is the inverse? How would the installer know? Both wires have black insulation, at least in my area. Would he have to climb the pole and check primary and secondary wiring? Would he have to ascertain which phase of the wye was used? Would he have to consult an IEEE standard?

Maybe he is supposed to, but I'll wager that most are too rushed to do all that and just flip a coin. In that case we must assume that it could be either and treat both V1n and V2n as being of equal importance. They both shock with equal strength. I know, been there and done that.

If V1n and V2n are of opposing phases, then V12 = 240V

If V1n and V2n are of the same phase, V12 = 0.

But that can't be now, can it??

Well, if the electrician subscribes to the view that the source is a three terminal black box with a magic voltage genie inside, if the genie says flip a coin, he has to do what the genie says. It's a short distance from subracting when adding to coin flipping.

If the electrician knows the source is two matched windings in series, he subscribes to a view of the source's underlying physical reality. This is far more knowledge than the coin flip can provide. This knowledge of the facts provided by the factory specs says the windings are matched and identical, share the same iron core and flux, same turn direction, and for the 120 0 120 system are connected in series. The windings physically add and to do so they must be physically "IN PHASE". The windings can also be connected parallel, odd terminals together (X1 + X3), even terminals together (X2 + X4), because the windings are matched and in phase.

This knowledge is consistent with how the transformer is actually built. There is no need to resort to the magic voltage genie, which is the same as saying 'rain is angels crying'.

Measuring the voltages relative to the neutral, the measuring convention is the abstract construct and the transformer is the real set of facts. Yes, a polarity reversal is available at the output of the transformer. This becomes a real measurement when you connect your leads in reversed polarity relative to the other winding, the scope says the phases are x(-1) or displaced by 180 deg. The phase shift is caused by how the leads are connected to the output relative to the two windings, the polarity is reversed at the output, not by the magic voltage genie, by the observer.

 

[jim dungar]

Which also means that:

Vmsin(ωt) ≠ Vmsin(ωt+π)

Thus two waves.

One phase, the two waves are inverses of each other. Remember the starting premises has been Van = Vnb=-Vbn based on cutting a single winding in half to create a center tapped winding of 120/240V. You seem to be forgetting the equality.

Go ahead show us the oscilloscope for Vm*sin(wt) sharing a common node with Vm*sin(wt+180), Mivey, previously supplied a circuit demonstrating this connection (I recall he labeled the paralleled voltages as Vnb=120@0? and Vbn=120@180?).

 

[jim dungar]

But that can't be now, can it??

No, it can't be.
If V1n and Vn2 are of the same phase then V12=240V
If V1n and Vn2 are inverse to each other then V12 = 0V.

It is simply physics.

But, I have know idea why the installer would care. He would do what any good circuit analyzer would do, He would arbitrarily assign a direction to one of the voltages and then compare it to the remaining one. He knows there is no such thing as a negative voltage, so he swaps his leads and off he goes.

If V1n and Vn2 are of the same phase then V12=240V
If V1n and Vn2 are inverse to each other then V12 = 0V, and something needs to be swapped.

 

[rattus]

No, it can't be.
If V1n and Vn2 are of the same phase then V12=240V
If V1n and Vn2 are inverse to each other then V12 = 0V.

It is simply physics.

But, I have know idea why the installer would care. He would do what any good circuit analyzer would do, He would arbitrarily assign a direction to one of the voltages and then compare it to the remaining one. He knows there is no such thing as a negative voltage, so he swaps his leads and off he goes.

If V1n and Vn2 are of the same phase then V12=240V
If V1n and Vn2 are inverse to each other then V12 = 0V, and something needs to be swapped.

BUT, if V1n and Vn2 are of the same phase, then V1n and V2n are NOT, and that is the issue!

You just can't accept the neutral as a common reference node can you?
You ought to be on Dancing With the Stars. You could win.

 

[Besoeker]

One phase, the two waves are inverses of each other. Remember the starting premises has been Van = Vnb=-Vbn based on cutting a single winding in half to create a center tapped winding of 120/240V. You seem to be forgetting the equality.

That may have been your premiss.
Remember that the discussion is about residential wiring. There are two 120V circuits. They are not the same as each other. They are mutually displaced by 180deg.

I'll post this yet again:

This circuit works because there are two sine waves. Two is not single. Simples to quote the meerkats.......UK television commercial.
Why otherwise would the circuit require two firing pulses per cycle?
Care to explain away that little inconvenient truth?

 

[Besoeker]

One phase, the two waves

Your post #2317 - One wave, one phase!
My response in post #2325 - Thus two waves.

So, maybe we are making progress!
You've gone from one wave to two waves within a few short posts. Now, we just need to continue the good work and help you to understand that there is more than one phase at work here.

 

[ggunn]

The grass is green! No, the sky is blue!

 

[gar]

120319-0841 EDT

Jim:

With two terminals (two wires) we have a single phase, call it phase A if you want (the naming use of phase).

Within the waveform of this phase we can make measurements of how far one point on the wave is with respect to another point in phase displacement units along the phase axis.

When there are more than two terminals, then more than one phase exists to provide names to identify these different sources.

Two or more of these phases might be identical and thus their waveforms would exactly coincide with each other. These phases would be described as "in-phase" or "same phase".

By general usage waveforms that are identical except for an amplitude difference are also described as "in-phase". Note amplitude is only a positive number.

When waveforms that share the same period (frequency) are different in shape, then there has to be a definition of what point on each waveform is the reference point for making comparisons between the waveforms. When comparing two sine waves one might pick the positive peak, and a sine wave with a sawtooth also might use the positive peak of each. Also the positive slope zero crossing is a popular choice. A sine wave compared to a square wave would most certainly use a defined slope and zero crossing because there is no unique maximum positive point for the square wave.

In normal usage, as we have shown in many different references, a sine wave and its inverse or 180 degree shifted wave are not "in-phase" or of the "same phase".

Anyone that is really familiar with circuit analysis will not classify V_AN and V_BN of a center tapped secondary as being "in-phase".

.

 

[rattus]

Well, if the electrician subscribes to the view that the source is a three terminal black box with a magic voltage genie inside, if the genie says flip a coin, he has to do what the genie says. It's a short distance from subracting when adding to coin flipping.

If the electrician knows the source is two matched windings in series, he subscribes to a view of the source's underlying physical reality. This is far more knowledge than the coin flip can provide. This knowledge of the facts provided by the factory specs says the windings are matched and identical, share the same iron core and flux, same turn direction, and for the 120 0 120 system are connected in series. The windings physically add and to do so they must be physically "IN PHASE". The windings can also be connected parallel, odd terminals together (X1 + X3), even terminals together (X2 + X4), because the windings are matched and in phase.

This knowledge is consistent with how the transformer is actually built. There is no need to resort to the magic voltage genie, which is the same as saying 'rain is angels crying'.

Measuring the voltages relative to the neutral, the measuring convention is the abstract construct and the transformer is the real set of facts. Yes, a polarity reversal is available at the output of the transformer. This becomes a real measurement when you connect your leads in reversed polarity relative to the other winding, the scope says the phases are x(-1) or displaced by 180 deg. The phase shift is caused by how the leads are connected to the output relative to the two windings, the polarity is reversed at the output, not by the magic voltage genie, by the observer.

I doubt that any electrician gives this a second thought. he just pulls the wires and tightens down the set screws as he has done hundreds of times before. He doesn't even question which is the 'real' voltage. He has equal respect for both--or better have!

No, the phase shift is caused by the way we define V1n and V2n. V1 is the voltage on L1 relative to the neutral; V2n is the voltage on L2 relative to the neutral. It is there whether we visualize it or not. It is there 24/7 just waiting to be utilized.

 

[jim dungar]

You just can't accept the neutral as a common reference node can you?

You really ought to read what other people post.
I have repeatedly said there are occassions where I use the neutral as a reference.

You seem to forget the concept of equality. Vbn=-Vnb two equal voltages share a common waveform. A common waveform means a common phase.
The principles of circuti analysis are the same regardless which reference is chosen, which is why I said it is an arbitrary choice.
In a single center tapped winding Van=Vnb=-Vbn=-Vna.

 

[jim dungar]

Your post #2317 - One wave, one phase!
My response in post #2325 - Thus two waves.

There is no progess unless you are finally admitting that the two halves of a single centertapped winding are IDENTICAL.
The number of voltage you derive are immaterial. The directions you arbitrarily assign are immaterial.

Van=-Vna=Vnb=-Vbn: It really is just about the equalities.

Van = 1 wave
Vbn = 1 wave
Vna = 1wave
Vnb = 1 wave

There are 4 waves of the same phase. Try to focus on the reality of the mathematical concept of equality.
A single center-tapped winding has 2 physically identical windings. Every mathematical manipulation must result in indentical results.

 

[jim dungar]

Anyone that is really familiar with circuit analysis will not classify V_AN and V_BN of a center tapped secondary as being "in-phase".

Van=Vnb=-Vbn=-Vna, what part of an equality do you have a problem with?

 

[ggunn]

That may have been your premiss.
Remember that the discussion is about residential wiring. There are two 120V circuits. They are not the same as each other. They are mutually displaced by 180deg.

I'll post this yet again:

This circuit works because there are two sine waves. Two is not single. Simples to quote the meerkats.......UK television commercial.
Why otherwise would the circuit require two firing pulses per cycle?
Care to explain away that little inconvenient truth?

No one here disputes the fact that the waveforms referenced to neutral of the A and B legs of a 240/120 split phase system are different, or why, or even what they look like. This thread is over 2300 posts of arguing over what to call it. Does it make any difference to an electrician wiring a house? Not in the slightest.

In my mind, inversion is not the same as 180 degree phase shift, although I stipulate that for an infinitely repeating pure sine wave the difference between the two is purely semantic. However, if you introduce a single, non repeating, short duration transient (which is terminologically triply redundant, I know) to the primary of that theoretical transformer with the A-N-B center tapped secondary, there is no value of phase shift that can be applied to the A terminal waveform referenced to N to make it look like the waveform at the B terminal referenced to N.

 

[gar]

120319-1045 EDT

Jim:

V_AN is not identically equal to V_BN and therefore with power applied to the transformer you can not connect terminal A to terminal B without sparks and high current.

.