Can "wattage" trip a GFCI?

[trader4]

What you are talking about is the relationship between voltage and current. If I put capacitance or inductance in a linear system, it changes the phase between the voltage and current. So, as you put it, they don't reach peak or zero at the same time. When plotted, the current and voltage are out of phase by a certain number of degrees. Whateve that shift is, you can describe it in degrees.

The phases under discussion here are pure voltage waveforms and are present without even having a load. With a

240V service, you have identcial sine waves which are mirror images of each other, between either hot and neutral. Take a sine wave and shift it by 180deg, ie one half cycle, and that is exactly what you have. So, you have two voltage waveforms that are 180 deg out of phase with each other. Hook up an oscilloscope and you can see it. Yet some are arguing that this then just becomes "it's just a negative", it's a case of plus and minus, etc. and can no longer be described as two phases which are 180 deg out of phase. Yet, there they are on an oscilloscope. Maybe someone can tell us this:

I can see these two distinct phases on those 3 wires of the 240V service with an oscilloscope. With 3 phase, I could do the same thing on that service and see 3 different phases, each seperated by 120 deg. Why is it that in the latter case, those on the other side of the argument here say there are 3 phases present, but in the former, there are but one, not the two on the oscilloscope? Posters dpb, Jeff and David and myself would describe both those services, their phases, in a consistent, logical manner.

Usual disclaimer: I did not just say, nor have I ever said that a

240V service is called a two phase service.

[David Nebenzahl]

On 1/17/2011 6:26 AM [e-mail] spake thus:

[snip]

[snip]

Thanks; I feel vindicated.

To throw out another example, I mentioned push-pull amplifiers in my earlier reply. These are almost always preceded by a stage called a phase splitter or phase inverter, which takes a signal and splits it into two phases, one 180° from the other. Every electronics engineer in the world would agree that this stage produces two distinct phases from a single phase. Which is exactly what our center-tapped transformer does.

Again, just to make it crystal-clear, the electrical industry uses the term "2-phase power" in a very specific way that does *not* include this way of generating two phases. Nonetheless, it does generate two phases, so technically speaking it is two-phase power.

Even if you would get laughed at by the power company for asking for a

2-phase transformer.

'K?

[bud--]

When the "phases" come from a single phase source (the utility transformer), and one of the "phases" is the negative of the other, calling them 2 phases makes no particular sense.

When I connect my 120-to-120V isolation transformer (for repairing equipment) to one of the "phases" is the secondary the "A" phase or the "B" phase?

This, of course, comes from a multi-phase source.

The voltages come from a single phase source (the service transformer primary is 2 wire). You get 2 phases from a single phase source?

The voltage on the secondary 2 wire combinations from that transformer are locked into either a positive or negative relation to other 2 wire combinations. When calculating currents in a 120/240V system with resistive loads you use plus and minus signs. Calling it 2-phase adds nothing useful and is not useful in calculations.

In the more general phasor calculations (which handle capacitance and inductance), a 120/240V system is represented as +120 and -120V (both "real").

Calling 120/240V "2-phase" makes as much sense as calling the old Edison

3-wire DC system 2-phase (at zero frequency).

Have a good trip.

[David Nebenzahl]

On 1/18/2011 9:49 AM bud-- spake thus:

I guess I'd have to call that question a red herring.

In the case of a transformer such as you describe, presumably with no center tap, then yes, there's only one phase. Only one set of conductors.

We're talking about something different: a center-tapped transformer, such as the utility company uses to deliver what's typically called "split-phase" power (i.e., 120-0-120).

There, you *do* have two phases.

The main objector in this discussion rejects this, apparently because they don't consider the "inverse" of a phase (meaning a set of conductors that's 180° out of phase with another set), to be a separate phase. But it is.

It's just that this is not commonly *called* "2-phase power": that refers to something else, specifically that obsolete system with one phase 90° to the other that's been described here.

Again: the output of a center-tapped transformer, whatever its use, is in fact 2 distinct and separate phases. But for some reason, it's not called that.

Now, I look forward to *your* comments on my comments ...

[bud--]

It is a minor illustration that "2 phases" is not useful.

It makes no sense to say you get 2 phases out of what is obviously a single-phase utility transformer.

From the wikipedia article

"it is sometimes incorrectly referred to as 'two phase'." (The article also suggests split phase is not the best name because of confusion with split-phase motors - which do start on 2-phases. I have never heard "split-phase" used for a 120/240V service.)

You can invent your own language. Where is any reasonable source that says a single phase transformer has 2 phases.

Not according to wikipedia. Find a transformer manufacturer that says their single phase transformer has secondaries that are 2 phases.

Not *commonly* called 2-phase? It is not *ever* called 2-phase. It is not a term used by any utility or manufacturer. It is a "single-phase" service, transformer, meter can, panel....

Wow, progress. You are right - "it's not called that."

It is not called that because it makes no sense. Voltages clearly comes from a single-phase transformer. The voltages of any secondary windings are locked into plus or minus relationships. The secondary is trivially understood with plus and minus signs. Calculations use plus and minus signs (not "phases"). Where inductance and capacitance are involved phasor analysis is used. A

120/240V service is characterized as +120 and -120.

It is not called that because it has no practical usefulness. (Except to cause confusion.)

[Twayne]

...

It's not called that because it is ONE phase coming from the powerco and is split to make two 120Vac lines into the residence. Thus the proper term is "split phase", not 2 phase. Although I hear 2 phase a lot, I know what they'e talking about so it's NBD to me.

Nah, it's just a bunch of egos here wanting to show how much they know and hoping their guesses are right for the most part. This is a useless thread with no useful information due to the interest in egoes rather than fact. It's typical of this newsgroup for the last year or so in fact and does no one any good. Post after post is filled with guesses and by gollies from those who feel the need to confuse, not assist anyone.

HTH,

Twayne`

[trader4]

It may be critical to the convention of what that 240V service is commonly called, but it doesn't alter the fact of how many distinct voltage waveforms are present. Going back to your example of the simple circuit with two balanced loads connected across the 240V hots, yes, in that case, you have only one phase. I cannot hook up an oscilloscope and see anything but one sine wave. As soon as you introduce the neutral, now I can see TWO different sine waves relative to the neutral, one being 180deg out of phase with the other. That circuit can now be described as having two phases.

Suppose I take a black box that consists of various linear circuit components and is powered by a 120V AC outlet. Inside that box, I have a common reference point. I ask students in a first year electrical engineering course lab experiment to graph the voltages at circuit points A, B, and C relative to the common reference point. I have the circuit designed so that the waveform at point B lags the one at A by 30 degrees and the waveform at point C lags the one at A by 180 degrees. I ask thefollowing questions:

What is the phase relationship between waveforms A and B?

What is the phase realtionship between waveforms A and C?

How many different voltage phases are there in the black box at points A, B, and C?

Do I need to know exactly how the voltages were generated, whether it came from a wall outlet, battery/inverter, trnasformer etc to answer any of those questions?

What is your answer? Is it that there are 3 phases or is that there can be only one, because it's originating from an outlet that has only one phase?

If your answer is that there are 3 phases present, then continue to the next part. I have another black box that merely consists of the 3 wire 240V service. The common reference point is the neutral, point A is one hot, point B, the other hot.

What is the phase relationship between waveforms A and B?

How many phases are present?

Note the usual disclaimer. I did not just say, nor have I said that the 240V service is commonly called two phase.

It's like I said earlier. If I went around telling people my son is a homosapien, or if I referred to water as dihydrogen oxide, it would be unusual and cause much confusion, because a lot of people wouldn't even know what it means. But that doesn change the fact that technically those definitions and terminology are correct.

Also, Bud's argument asking to find a center tap transformer manfacturer that calls their transformer two phase doesn't prove anything. I could just as well ask to find a capacitor manufacturer that says their capacitor can generate a 90deg phase shift.

This makes no sense at all. Why do I neeed 2 seperate secondaries? You are getting all hung up on where the power comes from. The mere presence of two voltage waveforms that are of different phases in a circuit, readily visible on an oscilloscope, is all that it takes to have two phases present.

[bud--]

Perhaps like your "guesses and by gollies" about power factor correction capacitors, using an oven neutral for a ground and class 2 power sources which were confused and completely wrong.

This thread is excessively about semantics.

[clare]

Forget it.\People will believe what people will believe, and no amount of explanation will get through.

[trader4]

How about this one:

"A pair of dots indicates like polarity.

Typically, the transformer will come with some kind of schematic diagram labeling the wire leads for primary and secondary windings. On the diagram will be a pair of dots similar to what is seen above. Sometimes dots will be omitted, but when =93H=94 and =93X=94 labels are use= d to label transformer winding wires, the subscript numbers are supposed to represent winding polarity. The =931=94 wires (H1 and X1) represent where the polarity-marking dots would normally be placed.

The similar placement of these dots next to the top ends of the primary and secondary windings tells us that whatever instantaneous voltage polarity seen across the primary winding will be the same as that across the secondary winding. In other words, the phase shift from primary to secondary will be zero degrees.

On the other hand, if the dots on each winding of the transformer do not match up, the phase shift will be 180o between primary and secondary, like this: (Figure below) "

Continue on in the above reference to the next section where the transformer that has two secondary windings, and keep the above discussion of phase in mind. They may not come right out and say it, but clearly you can have transformer outputs that are out of phase with each other, and hence, two distinct phases exist.

[trader4]

In other words, you won't answer a few basic, straightforward questions about phase that go directly to the core of the discussion, because to do so is impossible without contradicting yourself. I think those of us on the other side of this have answered and addressed all your questions/ issues with no problem.

[clare]

You can walk up the stairs, or you can walk down - and two people can walk up and down the stairs - does not make it 2 stairways.

[trader4]

You can try to side step with cute posts all you want, but won't answer the simple questions I posed that go to the core of the issue:

Suppose I take a black box that consists of various linear circuit components and is powered by a 120V AC outlet. Inside that box, I have a common reference point. I ask students in a first year electrical engineering course lab experiment to graph the voltages at circuit points A, B, and C relative to the common reference point. I have the circuit designed so that the waveform at point B lags the one at A by 30 degrees and the waveform at point C lags the one at A by 180 degrees. I ask thefollowing questions:

What is the phase relationship between waveforms A and B?

What is the phase realtionship between waveforms A and C?

How many different voltage phases are there in the black box at points A, B, and C?

What is your answer? Is it that there are 3 phases or is that there can be only one, because it's originating from an outlet that has only one phase?

Do I need to know exactly how the voltages were generated, whether it came from a wall outlet, battery/inverter, transformer etc to answer any of those questions?

If your answer is that there are 3 phases present, then continue to the next part. I have another black box that merely consists of the 3 wire 240V service. The common reference point is the neutral, point A is one hot, point B, the other hot.

What is the phase relationship between waveforms A and B?

How many phases are present?

Note the usual disclaimer. I did not just say, nor have I said that the 240V service is commonly called a two phase service.

[bud--]

I have no problem with: in-phase/out-of-phase additive/subtractive polarity or connection positive or negative polarity

To interconnect separate windings you have to know if the connection is additive or subtractive.

I have no problem with "two distinct phases" with regard to the current in the start and run windings for a single phase motor - there is a non-trivial phase angle that can vary over a wide range.

I have a problem with "two distinct phases exist" for a single phase transformer - the voltages on the distinct phases are always exactly opposite polarity. The "two distinct phases" are handled with trivial plus and minus signs (or dots). "Two phases" out of a single phase power transformer is guaranteed to cause arguments. "Two distinct phases" covers any phase angle and can lead to miscommunication.

David N's post that said: "but the 120+120=240 system we've been discussing actually is a 2-phase system, even though it's not really called that. One side is 180? out of phase with the other side, so by definition you have a 2-phase system."

It is, as I think almost everyone agrees now, not a "2-phase system". (David more recently writes in another newsgroup it is "truly two phase power".)

David also wrote: "Again: the output of a center-tapped transformer, whatever its use, is in fact 2 distinct and separate phases. But for some reason, it's not called that."

I agree - it is not called that. And I elaborated on why it is not called that. Like that in calculations you don't use 180 degrees out of phase. You use trivial plus and minus signs.

We have no disagreement on the physics, just the terminology. You can certainly use "180 degrees out of phase" or "different phases" if you want. IMHO it is excessively complicated, not useful, and can lead to confusion, miscommunication, and error (as by David).

The people who have objected mostly work with power systems, including multi-phase power systems. You will not likely find anyone in the power industry who considers a trivial 180 degree fixed shift a different phase.

[bud--]

Actually, I have no objection to saying the "A-leg" is 180 degrees out of phase with the "B-leg" either (though I would state it differently).

I have a problem with making them different "phases".