Is split-phase AC the same as "regular" AC?

[Analog Kid]

OK, so let's go to basics:

What is the definition of an electrical phase?

(And by "electrical" I do not mean "the electrical industry and common usage among electricians", but the technical definition of wave relationships.)

[Analog Kid]

Don't we consider a push-pull amplifier to operate on two separate phases, 180° apart?

We speak of "phase splitters", do we not?

[Monkeh]

Fuck me, here we go again.. Time to break out the metric rulers to fend him off. Begone, foul beast.

[Analog Kid]

Fuck me, here we go again.. Time to break out the metric rulers to fend him off. Begone, foul beast.

There's your fucking snobbery on parade again, bub.

[IanB]

How can you tell me that these waves don't constitute two different phases?
...
And yet if one of them is shifted by 1° then we can call them two phases?

In vector algebra, if two vectors are parallel to each other, you do not have a basis for a phase space. You need two vectors that point in different directions to have a basis.

If two vectors have the same direction but differ in the sign of their magnitude, then they are parallel to each other, and are thus not independent. Both vectors are multiples of the same basis vector, and thus you only have a single phase.

Phase angles have to be thought of like a clock. If one arrow points to 12 o'clock, and another arrow points to 6 o'clock, then the only difference between them is the sign (one positive, one negative). You can get an arrow pointing at 6 o'clock if you multiply the 12 o'clock arrow by a negative number. There is no rotation involved, only magnitude.

[brucehoult]

How can you tell me that these waves don't constitute two different phases?
...
And yet if one of them is shifted by 1° then we can call them two phases?

In vector algebra, if two vectors are parallel to each other, you do not have a basis for a phase space. You need two vectors that point in different directions to have a basis.

If two vectors have the same direction but differ in the sign of their magnitude, then they are parallel to each other, and are thus not independent. Both vectors are multiples of the same basis vector, and thus you only have a single phase.

In my house I have ethernet extenders that plug into power sockets and transmit the data on the power wiring. If I plug all of them into sockets that share the same phase they communicate with each other. If I plug one into a socket that is on the other phase then it can't communicate with the others.

That's "independent".

I'm not in the least bit interested in taking 0.5 of phase 1 and -0.866 of phase 2 in order to make yet another phase. I'm not running industrial machinery or doing mathematics, I'm just plugging in appliances in my house.

I don't agree that two electrical circuits with a common neutral in phase opposition are any less "2 phases" than two electrical circuits with a common neutral that are in quadrature or two electrical circuits with a common neutral that are 120º out of phase with each other.

If you want quadrature then say "two phases in quadrature" don't hijack the entire definition, most especially since 120º and 180º are the angles you actually find in the modern world.

[Analog Kid]

I don't agree that two electrical circuits with a common neutral in phase opposition are any less "2 phases" than two electrical circuits with a common neutral that are in quadrature or two electrical circuits with a common neutral that are 120º out of phase with each other.

Wait wait wait ...

Are you saying ... that you agree with my argument here? Maybe kinda sorta?

If so, I can die happy.

[IanB]

In my house I have ethernet extenders that plug into power sockets and transmit the data on the power wiring. If I plug all of them into sockets that share the same phase they communicate with each other. If I plug one into a socket that is on the other phase then it can't communicate with the others.

That's "independent".

I'm not in the least bit interested in taking 0.5 of phase 1 and -0.866 of phase 2 in order to make yet another phase. I'm not running industrial machinery or doing mathematics, I'm just plugging in appliances in my house.

I don't agree that two electrical circuits with a common neutral in phase opposition are any less "2 phases" than two electrical circuits with a common neutral that are in quadrature or two electrical circuits with a common neutral that are 120º out of phase with each other.

If you want quadrature then say "two phases in quadrature" don't hijack the entire definition, most especially since 120º and 180º are the angles you actually find in the modern world.

Language is about communication. If you want to be understood by other people, then you need to use a common language.

For your own private purposes, you are free to use whatever definitions you like. Feel free to disagree with industry norms.

But as far as electrical engineers are concerned, a split phase supply is a single phase supply. Like it or not, that is what the industry has adopted as their terminology.

I'm not an electrical engineer, and I also disagreed with this convention when I learned about it, but as I explained above, there is a reasoning behind the madness. So there is a choice: speak the same language and be understood, or speak a different language and face communication problems.

[Analog Kid]

For your own private purposes, you are free to use whatever definitions you like. Feel free to disagree with industry norms.

But as far as electrical engineers are concerned, a split phase supply is a single phase supply. Like it or not, that is what the industry has adopted as their terminology.

Care to address the question I posed above about why we refer to two phases in a push-pull amplifier?

[brucehoult]

Language is about communication. If you want to be understood by other people, then you need to use a common language.

I note when when I said I had an incident where half my power sockets were at 140V and the other half were at 340V everyone talked about it in terms of two phases.

Which I agree with.

[IanB]

Care to address the question I posed above about why we refer to two phases in a push-pull amplifier?

Well, for one thing:

I'm not an electrical engineer

So I'm not part of the "we".

But secondly, a push-pull amplifier output stage is a split phase circuit delivering a single phase output. The loudspeaker (load), sees a single phase AC input voltage at its terminals. It doesn't know or care what the amplifier is doing to deliver that.

So no, there are not two phases. There are phase and anti-phase components inside the amplifier circuit, which combine to give the two halves of the single phase output.

[Analog Kid]

But secondly, a push-pull amplifier output stage is a split phase circuit delivering a single phase output. The loudspeaker (load), sees a single phase AC input voltage at its terminals. It doesn't know or care what the amplifier is doing to deliver that.

So no, there are not two phases. There are phase and anti-phase components inside the amplifier circuit, which combine to give the two halves of the single phase output.

Hopefully not to belabor the point, but I'm referring to the innards of the amp, not its output.
The stage that delivers the two signals 180° apart is commonly referred to as a phase splitter, so how are those (internal) signals not distinct phases?

Or riddle me this: why would we refer to two signals at 0° and 179°, say, as proper phases but not signals at 0° and 180°?

Seems like a distinction without a difference to me.
But what the hell do I know? I ain't an electrical engineer either.

[Fried Chicken]

This whole argument can be solved with a relatively simple math equation

[brucehoult]

This whole argument can be solved with a relatively simple math equation

The maths is certainly simple.

And, yes of course, for some purposes it is more useful to have two phases with a significantly non-zero dot product. And for other purposes that doesn't matter at all.

That doesn't make phases with a zero or small dot product not phases.

[IanB]

Hopefully not to belabor the point, but I'm referring to the innards of the amp, not its output.
The stage that delivers the two signals 180° apart is commonly referred to as a phase splitter, so how are those (internal) signals not distinct phases?

You answered your own question: a phase splitter ties directly into having a split phase system.

[IanB]

The maths is certainly simple.

And, yes of course, for some purposes it is more useful to have two phases with a significantly non-zero dot product. And for other purposes that doesn't matter at all.

That doesn't make phases with a zero or small dot product not phases.

Well sure, you can call them phases. I would call them phases too. But as far as the industry is concerned it is not a "two phase system".

Don't argue with me, argue with them.

[IanB]

This whole argument can be solved with a relatively simple math equation

It absolutely can't, because the debate is about words and language, not about math. You can only address the argument using words, and their commonly accepted meanings.

[Analog Kid]

Well sure, you can call them phases. I would call them phases too.

Thank you; we're in agreement here.

But as far as the industry is concerned it is not a "two phase system".

Don't argue with me, argue with them.

It's a nonsensical distinction on their part.
But as I said, I never expect to win that argument.

[paul cotter]

As another poster said "if one can show rotation then there is more than one phase, if not it is single phase", or word to that effect. In amplifier tech to drive a push pull output one needs signals 180degrees apart- one can call this phase splitting, phase inversion or phase shifting, it does not matter. In power engineering the term phase has a somewhat different meaning, the common point between the two is a similar waveform that is or appears to be time shifted.

PS: I had a huge row with an electronics lecturer at college over exact wording. He referred to the phase shifter in an amplifier and I said that it is not a true phase shift but a phase inversion and I suggested a thought experiment where one would put a tiny spike on the waveform to find out has it been time shifted(phase shift) or inverted. He did not like my attitude and his answer was that the waveform would no longer be strictly sinusoidal and therefore phase was irrelevant. I considered this to be bullshit.   

[pdenisowski]

I note when when I said I had an incident where half my power sockets were at 140V and the other half were at 340V everyone talked about it in terms of two phases.

I had an incident where I lost one of the phases to my house - only half of the house had power and the utility company had to bring a special transformer to supply the "missing" phase while they corrected the issue on their end.  So yeah, kind of looks like two independent phases

[Siwastaja]

Because single-phase is bipolar, it defines two rotating vectors 180deg apart: motors demonstrate that perfectly, single-phase motors have two set of coils driven 180 deg apart, which push and pull alternatively. There is no concept of split-phase motor because it adds exactly nothing: the same "two phases" 180deg apart can be had by simple polarity reversal from a single supply!

Two-phase motors exist, most notably capacitor-run single-phase motors, stepper motors, and some BLDC fan motors. Distinctive feature is the 90deg phase shift: the bipolarity of the signal itself creates the two more 180deg out-of-phase versions; so a 1-phase motor has 2 poles, 2-phase motor has 4 poles. And yes - in some cases, some people call 2-phase motors 4-phase motors, the same confusion.

That's the practical version of the theory.

Note the difference to DC/DC buck converters: 2-phase buck does have 180, not 90 deg phase shift. This is because the construction is unipolar. In DC/DC buck, 180 deg phase shift doubles the ripple frequency. In bipolar, sinusoidal AC systems - think about full-bridge rectifier - 180 deg out-of-phase separate supply adds exactly nothing (in full bridge diode example, diodes already utilize both polarities).

Split phase AC is like two batteries in series. It offers a center tap for a half-voltage point, nothing more, that's it. Putting 3 AC supplies in series does not make 3-phase power, either.

Transformers with a lot of taps are plentiful. No one in their right mind would call them 5-phase or 9-phase power supplies.

Tapping out intermediate voltages out of AC supply does not generate "phases". The mental trick of choosing one of them as ground/reference level does not change this.

There are people, especially electricians, who use the word "phase" more loosely, kind-of replacement for the word "circuit". They are free to do so. With a split phase (3 wires) entering the house, saying "phase A" and "phase B" is unambiguous, and unnecessary pedantism is tiresome. But here, the OP wants to understand what it really is, and for that, the answer is simple, split-phase is regular single-phase AC with a center tap for half the voltage. That's it.

But the word split-phase exists exactly because it isn't 2-phase system. The word "split" itself suggests that the origin is singular: a single one is being split. 2-phase power distribution did exist. The words are not random, they carry real meanings and history.

[Analog Kid]

Look: do we not say, without any objection from anybody, that two signals are out of phase with each other if they're 180° apart?

Therefore those signals represent two different phases. Never mind that some people consider that a triviality because one signal is "only" an inversion of the other one, as if 180° is some kind of boogeyman magic number to be avoided.

And the hell with what the hidebound electrical industry considers proper terminology.

I'll still never win this damned argument ...

[paul cotter]

What you are saying is correct, no need to win any argument. In power engineering a separate phase refers to a supply that has rotation with respect to the original.

[rsjsouza]

This discussion led me to search around and, while I agree with the idea that wires carrying electricity at 180° of phase displacement is indeed a two-phase system, I also imagine that the terminology of "phases" for power electricity is intrinsically related to one of its main uses - i.e., to power electrical motors.

A system with 180° of phase displacement will not be able to cause a motor to spin on its own (at least not without the centrifugal switch), thus I imagine they found a need to differentiate that from a two-phase system that is described in the article below

Articles where I got these ideas... 
https://en.wikipedia.org/wiki/Two-phase_electric_power
https://en.wikipedia.org/wiki/Split-phase_electric_power

[paulca]

What Im curious about is 180 does not divide into 360 by any factor of 3.  So how do you get 180* phases from a 3 phase source?