Why is residential wiring known as single phase?

[pfalcon]

LoL. Finished this discussion in another thread after Besoeker dropped out of the discussion.
I should spin my head around and exclaim "It's BAaaaACK".

Pragmatically, if all you're servicing on residential 120/240 are 120V outlets; you can call it single-phase or two-phase. It won't matter until you hook up a dryer, water heater, stove, or similar device that wants both hots. To make those devices work the current/voltage must be "In Phase" and "Additive". Leading or lagging "A" or "B" will distort the entire phase "AB" not just "AN" or "BN".

Grounding and measuring from the center of the phase is called "Voltage Division". It's a really basic concept that can be done with either AC or DC voltages. And when we do it with DC voltages no one suddenly pops up and exclaims "It's TWO phase!". And yet ... wait for it ... if we put it on an oscilloscope we can see two amplitudes of opposite polarity! Which strictly speaking is an AC sign wave with an infinite wavelength and/or zero frequency!

When the pilot looks at the skydiver he says he's "down there" while everyone on the ground says he's "up there" and the diver says the pilot is "up" and the onlookers are "down". No matter where you put your probes for the oscilloscope, when the circuit "peaks" - A/B is DOWN while B/A is UP and N is halfway in-between. An oscilloscope tapped at N isn't showing "Phase difference", it's showing "Voltage division"; nothing more.

 

[iwire]

Why is it that the holders of the 180? phase difference methodology make it seem as though it is some sort of absolute? That all others must follow their rules? That it somehow re-defines the system? When in fact it is simply a chosen point of reference?

If it weren't for these absolute statements made by these people, these arguments would not be happening. :rant:

From an outsider looking in it appears both camps are guilty of speaking in absolutes.

If it weren't for the deliberately deceptive comments, these arguments would not be happening. :rant:

Lets not go there OK, I don't think any one is deliberately trying to mislead, they just strongly believe in their position.

 

[rbalex]

I hereby nominate “Why is 120/240 called ‘single-phase’?” as the fourth TABOO subject. With links to Why is residential wiring known as single phase?, Is it Single or Two Phase? and 240v debate.... for the curious

 

[Rick Christopherson]

From an outsider looking in it appears both camps are guilty of speaking in absolutes.




Lets not go there OK, I don't think any one is deliberately trying to mislead, they just strongly believe in their position.

To the untrained, it may seem as just a simple disagreement. The reason why these discussion get so heated is because to those of us that understand the system, it is deliberately deceptive. That's what ruffles feathers. That's what causes arguments.

Mathematically both approaches are correct, so you wouldn't be getting arguments from engineers and PE's over simple mathematics. You're getting arguments because some people are so headstrong in convincing the world about their view that they are willing to mislead other people in the process.

If it wasn't for the deliberate misinformation, this thread would have ended on the first page. No one would be arguing, because the math is the same either way.

 

[iwire]

To the untrained, it may seem as just a simple disagreement. The reason why these discussion get so heated is because to those of us that understand the system, it is deliberately deceptive. That's what ruffles feathers. That's what causes arguments.

Mathematically both approaches are correct, so you wouldn't be getting arguments from engineers and PE's over simple mathematics. You're getting arguments because some people are so headstrong in convincing the world about their view that they are willing to mislead other people in the process.

If it wasn't for the deliberate misinformation, this thread would have ended on the first page. No one would be arguing, because the math is the same either way.

Rick,

What also cause arguments is people calling others 'deliberately deceptive' and insinuating that they are somehow less than you because they don't agree with you. (And I am not talking about me, I am talking about the others that have training and experience similar to yours.)

So I am asking you, very politely, very nicely to curb the talk of deception, misinformation and lack understanding and stick with the facts of the discussion.

Thank you.

 

[iwire]

I hereby nominate ?Why is 120/240 called ?single-phase??? as the fourth TABOO subject. With links to Why is residential wiring known as single phase?, Is it Single or Two Phase? and 240v debate.... for the curious

I think it is time for that as well.

This can be the engineers equivalent of ground up or ground down.

 

[Rick Christopherson]

You're right. It's better to sweep it under the rug and let the battle ensue than to face it head on.

 

[iwire]

You're right. It's better to sweep it under the rug and let the battle ensue than to face it head on.

If you are correct in your view on this threads topic you should be able to show it without disparaging others.

Not a tough request and one that I would ask of anyone in this thread.

 

[jim dungar]

With my notation,....(current entering a node must equal current leaving a node.)

.... Ib leaving the source at B.....

.... Ib=-IL2.

So if IL2 is the current entering the node, then Ib must be the current leaving the node which would mean Ib=IL2, but you are reporting Ib=-IL2.

 

[Rick Christopherson]

If you are correct in your view on this threads topic you should be able to show it without disparaging others.

Not a tough request and one that I would ask of anyone in this thread.

That's the point, Iwire. Both sides are correct, and both sides KNOW they are both correct. But only one side is trying to convince other people that there is only ONE way. That's the misinformation.

BTW, I am not disparaging anyone. I am simply talking about the topic itself.

 

[rbalex]

Person 1: "2+2 is 4."
Person 2: "No, no, NO; 2-(-2) is 4."
Person 3: Well yeah - you both have that part of the math right; but it doesn't have anything to do with what a phase is.

 

[jim dungar]

I think it is time for that as well.

This can be the engineers equivalent of ground up or ground down.

Sorry but it is more important than that.
If I ask you to connect power quality metering is it important to know the relationship between the CT and voltage connections?


Trying to use analogies like standing in the middle and looking up hill or down hill do not adequately represent this discussion.
A better analogy would be 2 cars moving from point Y towards point Z, one driver decides to face point Z and drive with the car in forward, and the other decides to face point Y and drive with the car in reverse. So would you say the two cars are moving in different directions? How about the cars are moving 180?opposite each other? Isn't the actual result both are moving towards the same place?

 

[TimWA]

OP here, wow, what's all this?

OP here, wow, what's all this?

18 pages? Everyone must be celebrating the simple and definitive answer I posted on page 3 to my own question.

 

[gar]

120201-1839 EST

I have not wanted to get back into this going nowhere discussion. But for this one post I will.

It is all about a clear definition of the word phase.

One choice is to define two signals as being in phase if:
1. Both are of the same magnitude.
2. Both are of identically the same frequency.
3. Both are pure sine waves.
4. and when connected in parallel there is no current flow between the signal sources.

This clearly does not include a center tapped transformer


Another less limiting definition is:
1. Both signals are identically of the same frequency.
2. Both signals have positive zero crossings at identically the same times, or alternatively based on identically occurring negative zero crossings.

This clearly does not include a center tapped transformer when the center tap is the measurement reference point.


I am flexible and tolerate various uses of the word phase.


.

 

[kwired]

That's the point, Iwire. Both sides are correct, and both sides KNOW they are both correct. But only one side is trying to convince other people that there is only ONE way. That's the misinformation.

BTW, I am not disparaging anyone. I am simply talking about the topic itself.

And the discussion has pretty much had the same success as the ground up / ground down discussion.

 

[Hv&Lv]

Only 424 more posts to go...

 

[jim dungar]

And the discussion has pretty much had the same success as the ground up / ground down discussion.

Don't I wish.

To me, it seems every time someone says the two halves of a single transformer winding are in phase, someone else jumps in to say that is wrong. Not that it is a matter of personal preference, but rather it is 'totally' wrong.
As it was emphatically said in post #89:

But, if the two voltages are at different potentials wrt neutral, you can't reasonably say that they are in phase.

I believe part of the problem has to do with the lack of a definition of the word 'phase'.
I do find it interesting the majority of the posts in this thread are made by members who have not participated in previous discussions of this topic.

 

[david luchini]

So if IL2 is the current entering the node, then Ib must be the current leaving the node which would mean Ib=IL2, but you are reporting Ib=-IL2.

Nice try, but read it again. If the Node is the connection from Line B to the load #2, then Ib is entering that node from the source and IL2 is entering the node from the load #2. Ib+IL2=0, or Ib=-IL2.

 

[rbalex]

I guess I?ll make this my last post on the subject too.

I?m not saying polarity is unimportant nor am I saying magnitude of potential difference (voltage) is unimportant. I am not saying they aren?t potentially affected by phase; however, I am saying they, as well as zero crossing are irrelevant in defining phase.

The OP asked why we call residential 120/240 single phase.

Assuming the equipment is properly installed; write any set of voltage functions for a 120/240V secondary as a function of time with respect to any arbitrary reference point. If written correctly and properly reduced, they will all eventually resolve to:

V(t)_lL-L= ? 240 sin (ωt +φ₀) or
V(t)_lL-N= ? 120 sin (ωt +φ₀)

The phase value, common to all the voltage functions, is (ωt +φ₀); this is why we call it ?single-phase?

Zero crossing is simply a special case where (ωt +φ₀) = 0, but it is not necessary to define the phase of the function.

 

[jim dungar]

Nice try, but read it again. If the Node is the connection from Line B to the load #2, then Ib is entering that node from the source and IL2 is entering the node from the load #2. Ib+IL2=0, or Ib=-IL2.

Oh I see, KCL talks about current entering a node and current leaving that node. But, you have decided that both currents are entering this particular node.

Following the same logic then shouldn't Ia=-(IL1+IL2).

Instead of messing with your definition of KCL, wouldn't it be easier to solve the equations using Vnb instead of Vbn?