three Romex sets in ceiling box

[gfretwell]

Or a grounded conductor.

Pretty soon you are going to be in a semantics discussion about why 2 conductors of a 3 phase are single phase.

[gfretwell]

No we are talking about wye distribution with one phase conductor and a grounded conductor although there will always be some earth return. Measuring the grounding conductor coming down the pole from each transformer on my street that earth return varies from around a half amp up to almost 3. I also see current on my service neutral with the main breaker off but I probably have the best GES on the street so I get a lot of that current.

[gfretwell]

Liquid, solid or gas

[gfretwell]

12, 3, 6 and 9 on your clock are 90 out and they are very symmetrical.

You might be able to create a 100 degree phase shift with electronics (using a capacitor like starting a motor) but not in an alternator.

>

[trader_4]

It's not electrically useless, it's how 240/120 is delivered to your house on 3 wires. And your graph sure shows two phases, separated by

180 deg. How would you describe that, if not two sine waves, one 180 deg out of phase with the other?

[trader_4]

OMG. There is no 12, 3, 6 and 9. In Ralph's 100 year old 90 deg two phase example, there is only 12 and 3. Twelve being 0 degrees and 3 o'clock being 90 deg. Two windings that are 90 deg separated in phase. Nothing symmetrical about that.

Double OMG. It's very simple. We have two alternators on a common shaft. Each produces a sine wave voltage. They are arranged so that one winding is shifted 90 deg from the other. Yes? Just loosen up the winding on one and rotate it ten more degrees. Now you have 100 deg separation. It's quite amazing you appear to believe that in fact

90 deg is somehow special, sacred, unique and that any other phase angle can't just as easily be produced, by simply rotating the winding of one of the alternators.

[trader_4]

No, it's not an artifact, you're seeing exactly what is there. You act like I want to hook the scope ground to some bizarre point, like out in space or tied to a water bucket. In fact, it's being hooked to the neutral, which is the common system reference point. Do you deny that 240/120 looks like and behaves exactly like two

120V voltage sources that are 180 deg out of phase with each other?

And again, if you would follow the very simple example I gave using Ralph's 90 deg two phase, you'd see how electrically it is the same as 240/120 with the exception that the phase angle is 180, instead of

1. Again:

Ralph's two phase is two phase, yes? It was three wires, 0 deg phase hot, 90 deg phase hot, common neutral return, yes? OK, make it 100 deg phase difference, which of course we could easily do. Would there still be two phases there? Make it 179, still two phases? Make it 180, what do you have now? Still two phases or did something mysterious just happen? And don't say those phases are "weird", it's irrelevant. We can write the equations, solve them, for any phase angles we want. Of course the answer is that there are still two phases there. And then what you have is electrically the same as the 240/120 service. They are indistinguishable. That's the beauty when you approach things like an engineer, logically. If you don't treat it that way, then you have holes where what should be elegant, logical and continuous, falls apart.

[Clare Snyder]

In 3 phase it's all 120 degree phase shift. If you connect the scope across a single phase, of course that is all you will see

[Dean Hoffman]

Cut a bunch.

Question. Would the two phase motors from days of yesteryear start without capacitors?

[Mike Oxbern]

Look like what I'd expect to see with a two channel scope.

Trace 1:  common on L1, signal on L2

Trace 2:  signal on L1, common on L2

Again, would you like to buy a magic dual-polarity AA battery?

[trader_4]

What happened to the NEUTRAL? Do you deny that 240/120V into a house is TWO 120V sine wave voltage sources, that are 180 deg out of phase with each other or "of opposite polarity', which is the same thing? That is the only way you get 240/120 on three wires.

Or try answering the simple questions I posed from Ralph's example of two phase, 90 deg power from 100 years ago. It was two phase, 90 deg apart, on three wires, two hots, common return. Rotate one winding so instead of 90 deg, it's 100 deg. Are there still two phases there? Rotate it to 179 deg. Still two phases? Rotate it to 180, what happens now? What you have at 180 is exactly what you have on 240/120V into your house.

[trader_4]

Yes.

[gfretwell]

I don't know what ralph drew but 2 phase 5 wire looks like a clock

[gfretwell]

There is nothing bizarre with corner grounded delta and any single transformer is exactly like the one in front of your house.

[Clare Snyder]

For the same reason a 3 phase motor self starts. What does a capacitor do? it puts the current out of phase with the voltage - and causes the magnetic field to effectively rotate. Same thing a multi-phase motor does - but the multi-phase motor does it much more efficiently. 2phase makes a noisy motor because it bsically gets "kick - rest ,kick

-rest, kick - rest - where a 3 phase gets kick-kick-kick-kick - with the kicks overlapping each other

[gfretwell]

Yes, just like a 3 phase motor since you already have a phase shift. That is another indication that single phase is just that, you still need a capacitor to create a phase angle no matter how you connect a single phase motor. They do make shaded poll motors that start without a capacitor but they do a trick with the shaded pole winding that makes it look like there is a phase shift. They don't have much starting torque tho.

[Clare Snyder]

On a 3 phase power supply each phase is a singlr phase power sourse - so will look like a single phase.

With a multi-trace scope, you overlay the phases and see them displaced by 33.3% - or 120 degrees

On the old 2 phase system you would find the 2 phases overlap by 25%

- or 90 degrees.

On a split single phase they overlap 100% - or 180 degrees Connecting the phases in parallel will cause a direct short circuit

[gfretwell]

But if I ground my scope and look at one of those corner grounded transformers I will see 120v (RMS) at the center tap and 240v at the opposite end, in identical phase relationship.

Trader's problem is he can't comprehend that 180 degrees is a straight line (I guess he had a bent protractor in school) and he starts trying to confuse the issue with impossible phase shifts.

[Dean Hoffman]

So doesn't that render our modern 240 vac single phase motors a special case? We call them single phase just because they don't do the same thing as the old two phase?

[trader_4]

I'd say your problem is you don't understand the definition of phase or it's concept. That's obvious in the above statement. A 180 deg phase difference means you have a periodic waveform that is shifted half a period with respect to the another periodic waveform of the same frequency. It's not a straight line anymore than the

90 deg angle in Ralph's old two phase example is a right angle. In the case of sine waves and similar, 180 phase difference is the opposite sine wave. In Ralph's example, it's a quarter period shift.

"As it can be seen from the figure that this type of configurations gives us two phases through the two parts of the secondary coil, and a total of three wires, in which the middle one, the center tapped wire is the neutral one. So this center tapped configuration is also known as a two phase- three wire transformer system."