Is it Single or Two Phase?

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Say you don't bond the center tap to ground and you measure the voltage from either A or C phase to the tap, can you tell me what that voltage will be? And exactly how that voltage is generated?
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It will be half the voltage of the full winding, and it is generated the same as any other voltage is generated. It is also transformed the same, the secondary winding will have be 1 to 1, 2 to 1, 3 to 1 or what have you depending on the higher primary voltage, OR reverse that if the primary voltage is lower.

This is simple transformer basics.

Why would you think the center of a windings voltage has anything to do with bonding?

If I wanted to derive 240 ungrounded voltage from a 480 volt winding, I would simply tap the winding at the center point and connect the other side of the circuit to either end of the winding. Barring code issues, I could do the same thing if I needed 120 ungrounded voltage from a 240 volt winding.

So see, the grounding or bonding of this point means nothing.

Roger
 
e57 said:
So we're talking about whats at your house Bob? Thats not fair... :cool:
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Well normally I would say your right....that is not fair but if we look at the opening post in this thread.....

iwire said:
I am interested.

IMO the 120/240 service to my house is Single Phase.

Some would say it is two phase.

Two phase is another system altogether that apparently was used in industry but is all but forgotten now.
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.....the question was always about my service. :D

If we where talking about the multifamily services in my area which are usually supplied 208Y/120 I would agree that the single phase panels in each unit are indeed supplied by two distinct phases but it is still not two phase.

Two phase (IMO) is a entirely different system that is described in detail if you follow the links provided in this thread.

If I made a six phase Wye system and used just two phases and neutral that section would still not be a 'two phase system'. It would simply be two phases of a six phase system.
 
iwire said:
.....the question was always about my service. :D I think I helped it getting so far out of your neighborhood - Sorry.

If we where talking about the multifamily services in my area which are usually supplied 208Y/120 I would agree that the single phase panels in each unit are indeed supplied by two distinct phases but it is still not two phase. True... We would not call it two-phase, it only lead to confusion :rolleyes:

Two phase (IMO) is a entirely different system that is described in detail if you follow the links provided in this thread. I think put up a few myself...
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But now we a name for all the ways to use those other ones outside of you neighborhood
 
e57 said:
But now we a name for all the ways to use those other ones outside of you neighborhood
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I don't think much changes.

2 hots and a center tapped neutral is not by the conventional definition 'two phase'.

Did you really install "Two Phase" that requires a 4 pole disconect switch.
 
Here is a service disconect switch for a true two phase system the type of two phase refereed to in Table 430.149 Full-Load Current, Two-Phase Alternating-Current Motors (4-Wire) of the NEC.

2phase2.jpg
 
roger said:
...

So see, the grounding or bonding of this point means nothing.
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Exactly, but that doesn't answer exactly how the half voltage is generated. There are only two possibilities as I see it: 1) the center tap is at a continuous 0 volts, or 2) the center tap is a phase-shifted output operating at an angle half-way between that of the two ends. Which is it?

From all the information I have read, I'm quite sure it to be the latter. What say you?
 
Smart $ said:
Sorry, I'm quite reluctant to giving out personal information. I really do appreciate the "tit-for-tat" attitude of putting the "tat" first, but that's as far as it goes. Hold it against me if you will, but that's simply the way it is.
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I did not ask for your address, phone number, bank account number or Mothers maiden name, just your qualifications.

You won't tell us anything about yourself

You won't answer simple questions when asked.

Well that speaks volumes about you and your credibility, or lack there of in this case.

You must not believe in what you post if you will not put your name on it.
 
iwire said:
I don't think much changes.

2 hots and a center tapped neutral is not by the conventional definition 'two phase'.

Did you really install "Two Phase" that requires a 4 pole disconect switch.
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No, but you know what I mean, don't you?

This picture says a thousand words at times Bob. :cool:

image.php


Where do I get one?
 
Smart $ said:
As for the o-scope, he's talking about meauring either referenced to the other, not referenced a steady state 0 volt reference. If you put L1 and L2 on separate channels and reference the measurement to steady state 0 volts, you will see each waveform is not the inverse of the other. They would be if it were a true single phase system.

Here's a question for the open minded. In the following diagram, what is the current on the neutral? The simple truth of the matter is, if the current is anything other than 0A, it is not a true single phase system.
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I know exactly what he is talking about.
smart $, I think you are making this stuff completely up. You might be a good electrician, but you are NOT a credible source for this discussion. Please stop confusing others that might be watching.
 
Education from the Dept. of Energy

Education from the Dept. of Energy

For forum members that may be confused about "phase" and other topics discussed here, just start another thread and we will stick to the basics of AC generation and transformation. I'll be glad to participate.;)

This is from Basic AC Theory:
When a voltage is produced by an AC generator, the resulting current varies in step with the voltage. As the generator coil rotates 360?, the output voltage goes through one complete cycle. In one cycle, the voltage increases from zero to "Emax" in one direction, decreases to zero, increases to "Emax" in the opposite direction (negative Emax), and then decreases to zero again.

Phase angle is the fraction of a cycle, in degrees, that has gone by since a voltage or current has passed through a given value. The given value is normally zero.

A term more commonly used is phase difference. The phase difference can be used to describe two different voltages that have the same frequency, which pass through zero values in the same direction at different times.

Phase difference is also used to compare two different currents or a current and a voltage. If the phase difference between two currents, two voltages, or a voltage and a current is zero degrees, they are said to be "in-phase." If the phase difference is an amount other than zero, they are said to be "out-of-phase."
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Smart,
Here's a question for the open minded. In the following diagram, what is the current on the neutral? The simple truth of the matter is, if the current is anything other than 0A, it is not a true single phase system.
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Are you saying the grouned conductor current is not zero in your drawing?
Don
 
Mr. $, regardless of how many taps there are on a single transformer winding, it is a single-phase system. The only significance of where (if at all) a ground bond connection is made is the voltage-to-earth from any other point.

If one were to ground one end of a 240v center-tapped winding, instead of the typical mid-point (120-0-120), the voltage-to-earth from each point would obviously be different (0-120-240), but it would still be a single-phase system.

An oscilloscope, just as with almost every test instrument, must use a reference point when displaying a voltage, since voltage is a potential-difference measurement between two points.

Just because there is a 180-degree timing difference when using a center tap as reference, and not when using one end as a reference, doesn't change whether a system is one phase or two.
 
billing/supply

billing/supply

Larry, very nicely put!

I happen to work for the POCO in my area, lets just say that if we were supplying "2 phase" power to anyone (residential), they will most certainly be getting a bill for 2 phase power. That is not happening!

-Matt

PS: How about this crazy heat wave! I guess they are saying this is the hottest first 6 months ever recorded (1895)!
 
Further, if you have two lines and a neutral from a 3-ph 208/120v system, there is 208v between the lines, and that 208v is single phase. The phase angle is what causes the voltage to be less than 120v + 120v. Delta does not have any phase shift, which is why line-to-line voltage is 120v + 120v.

On a 2-channel oscilloscope, with the neutral as ground reference, the 120-degree phase angle would appear as a 120-degree shift, exactly 2/3 of a 3-phase display, as you'd expect. However, measuring line-to-line can only be done with a single channel, and would appear as a single-phase sine wave.
 
mpross said:
I know exactly what he is talking about.
smart $, I think you are making this stuff completely up. You might be a good electrician, but you are NOT a credible source for this discussion. Please stop confusing others that might be watching.
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Actually, I'm a great electrician. :D I can be equally vain, perhaps even surpass as anyone here. But that is not my true nature, as I'm basically quite modest.

So far I haven't seen you post any authoritative evidence that proves me wrong. Until then...
 
Smart $ said:
Are we answering questions with questions now?
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It's really the only option we have at our disposal.

We're trying hard to understand where you're coming from. But just about every time you post something, someone asks you one or more clarification questions about what you posted, and you refuse to answer those questions.

It gets pretty tiresome, particularly since youre violating the spirit of informed, reasonable debate. When you state a position or post a diagram, and someone asks you about it, you're supposed to come back with an answer that moves the discussion forward. Posting another evasive maneuver instead is simply bad form.

Reading some of your posts kinda reminds me of something an old friend put on the web a while back: http://www.mindspring.com/~mfpatton/sclinic.htm :)
 
Thanks ceknight,

I was thinking the same thing.

Oh yeah smart $, I am not offering authoritative proof, because I am only a senior in EE and I still feel as though I have a long ways to go in the knowledge dept... ...but even if I wanted to give you a proof you probably wouldnt be able to follow the math.

For all others, I appreciate your posts, and I can tell many of you have a wealth of knowledge to offer! :)

-Matt
 
I don't care if you only use 2 legs of a 3 phase Y or only one. That is a 3 phase system with the unused phases at zero magnitude- at least at the specific load in question. The timing is 120 degrees on whatever phase you choose, even if you chose NOT to use the others. That timing is one reason single phase motors struggle across two legs of a Y system. The applied voltage- the amount of time the voltage is at the highest magnitude- voltage is lower because the voltage is limping along without a leg, no pun intended.

I believe someone earlier on hit it on the head when they mentioned phase and leg being different animals. When I think phase, I think timezone like we have running north and south across the planet. If you go farther north or south within a time zone (a leg) it may get hotter or colder and even change seasons but, it is the same TIME of day.
 
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