Why is residential wiring known as single phase?

[rattus]

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.

Doesn't happen when we assume pure sinusoids, although we get your drift.

 

[rattus]

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 = 120Vrms*sin(wt)
Vbn = 1 wave = 120Vrms*sin(wt + PI)
Vna = 1wave = 120Vrms*sin(wt + PI)
Vnb = 1 wave = 120Vrms*sin(wt)

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.

'

No, it is about the inequalities.

I see 4 waves, 4 equations, TWO phase constants, TWO phases. You don't seem to get that fact.

How can waves have differing phase constants and be of the same phase???

After all the argument of the sines describing the waves defines the phase.

 

[rattus]

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.

But 120Vrms @ 0 NE 120Vrms @ PI!

Let's get back to pure math. Is a sine wave and its inverse of the same phase???

 

[ggunn]

Doesn't happen when we assume pure sinusoids, although we get your drift.

Which I stipulated. To me, however, the correct solution to a problem is one which is true for all cases. In engineering school, if I had answered an exam problem by applying phase shift instead of inversion to show the difference between Van and Vbn, I would have gotten it wrong even though I had arrived at the correct answer.

 

[rattus]

Which I stipulated. To me, however, the correct solution to a problem is one which is true for all cases. In engineering school, if I had answered an exam problem by applying phase shift to show the difference between Van and Vbn, I would have gotten it wrong even though I had arrived at the correct answer.

No, it only has to be true for the conditions stipulated. Besides, the term 'phase shift' is too ingrained to expect to change its use. Like vectors when phasors are more descriptive. Like mivey says, "That ship has sailed."

 

[Rick Christopherson]

Let's get back to pure math. Is a sine wave and its inverse of the same phase???

From the pure math perspective, yes they are. Because as Jim stated in post #2337, Every mathematical manipulation must result in indentical results. That means that the analysis must be the same regardless which reference point you pick.

 

[ggunn]

No, it only has to be true for the conditions stipulated. Besides, the term 'phase shift' is too ingrained to expect to change its use. Like vectors when phasors are more descriptive. Like mivey says, "That ship has sailed."

I do not contest that the usage is ingrained and I am not stumping to change the vernacular. In the audio world the term "180 degrees phase shifted" for an inverted signal is and will always be widely used, and everyone knows what it means, though technically it is incorrect, just as it is here, for precisely the same reason.

Look at it this way: Are Van and Vbn 180 degrees out of phase with each other? Absolutely. How did they get that way? Was Vbn phase shifted or inverted from Van? Inverted. The fact that the end result is indistinguishable from a phase shift is immaterial. Whatever happens on the primary happens simultaneously on A and B. If there were a phase shift involved that would not be true.

FWIW and BTW, Van is also 180 degrees out of phase with Vna. Everything depends on your frame of reference.

 

[rattus]

From the pure math perspective, yes they are.

They are of the same phase even though their phase constants are different???

Can't be.

 

[Rick Christopherson]

They are of the same phase even though their phase constants are different???

Can't be.

Hey, you're the one that specified "pure math" in your question. Accept responsibility for your chosen words. From a pure mathematical perspective, all methods must result in the same solution. That includes the choice of whether you wish to show them in-phase or out-of-phase.

 

[rattus]

Hey, you're the one that specified "pure math" in your question. Accept responsibility for your chosen words. From a pure mathematical perspective, all methods must result in the same solution. That includes the choice of whether you wish to show them in-phase or out-of-phase.

That is pure math. The phase constants are different, ergo a sine and its inverse are NOT of the same phase. There is no way one can show a sine and its inverse to be in phase.

 

[Rick Christopherson]

That is pure math. The phase constants are different, ergo a sine and its inverse are NOT of the same phase.

No, from a mathematical perspective, the phase constants are different only because you have chosen to make them different. For every mathematical analysis that you can perform that uses different phase constants, I can replicate the same result without ever using different phase constants. That's why you guys can never resolve this from a mathematical standpoint.

 

[rattus]

No, from a mathematical perspective, the phase constants are different only because you have chosen to make them different. For every mathematical analysis that you can perform that uses different phase constants, I can replicate the same result without ever using different phase constants.

Well, why don't you replicate? Give us an example.

 

[Rick Christopherson]

Well, why don't you replicate? Give us an example.

:dunce:

rep?li?cate

1. Also, rep?li?cat?ed. folded; bent back on itself.

verb (used with object)
2. to bend or fold back: a replicated leaf.

3. to repeat, duplicate, or reproduce, especially for experimental purposes.

I'd be happy to, if you gave me something to replicate. Doh!

 

[rattus]

To be equal, two waveforms must be equal in BOTH magnitude and phase.

To be in phase or of the same phase, they must carry the same phase angle (phase constant), their +/- zero crossings must coincide, their -/+ zero crossings must coincide, their peaks must coincide, their troughs must coincide, in time of course. I have never seen a wave and its inverse meet these criteria, and I think I never will.

 

[rattus]

:dunce:
I'd be happy to, if you gave me something to replicate. Doh!

Just prove that sin(wt) is of the same phase as -sin(wt). No cheap tricks now.

 

[jim dungar]

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.

.

Please tell me who said it was.
You cannot connect terminal A to N or B to N without sparks either.

It is amazing how many posts have resulted from arguing points I have never made.

 

[jim dungar]

No, it is about the inequalities.

With a single center tapped winding there are no inequalties based on the physics behind the construction of the transformer.
The inequalities only occur based on your specific choice of assigning opposing voltage directions in your analysis. But when all the math manipulations are done the physics of the construction of the transformer remains.

Draw the "equivalent circuit" of a single primary transformer winding and a single secondary winding. What references would you cite, to have Vsec be of a different phase than Vprimary? Why does IEEE/ANSI waste space in their 'standards' describing the relationship between X1 and H1 terminals?

I have tried to maintain my focus on this 'unique' situation of a single center-tapped winding.

 

[jim dungar]

But 120Vrms @ 0 NE 120Vrms @ PI!

Let's get back to pure math. Is a sine wave and its inverse of the same phase???

No lets stay on the situation of a center tapped transformer where Van=Vnb=-Vbn=-Vna.

 

[ggunn]

A sinusoidal AC voltage is fed into the primary of a transformer with a center tapped secondary with terminals A, B, and N where N is the center tap. Van is connected to another transformer with a center tapped secondary, and Vbn is connected to yet another transformer with a center tapped secondary. Now how many phases do you have?

This is a silly argument.

 

[ggunn]

...the term 'phase shift' is too ingrained to expect to change its use. Like vectors when phasors are more descriptive. Like mivey says, "That ship has sailed."

And just like that you have answered the original question. Residential wiring is known as single phase because that's what we call it. Q.E.D. Check, please.