single vs. 3 phase
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hardworkingstiff
Senior Member
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- Wilmington, NC
mivey said:You might consider that GE has no problem with the term 120/208 single phase:
Mivey,
I know this is nit picking, but they did not call it a single-phase service, just that single-phase loads could be served.
I'll let it go, because I guess it really doesn't matter.
POWER_PIG
Senior Member
It's all very simple......and it's prob. been stated here in previous post, but forgive me for not going back in time to see. It's called single phase because there is only one phase. (pretty simple eh?) calling L1 and L2 "A" phase and "B" phase is where the confusion sets in. In a single phase installation there is only one secondary phase in relation to the primary. In a 120/240 install, you will have only one 240 volt " phase." Now bring out the center tap and now you have two half phases.....generally called line 1 and line 2 and they will read 120 line to neutral (center tap).
It's called 3 phase when you have 3 single phase pots (windings) wired in series or in parrallel depending on the config. A "wye " is 3 windings wired in parallel, and a "delta" is 3 pots (windings)wired in series. thats the just of it, until you get into 2 pot banks like an open delta secondary/open wye primary.
It's called 3 phase when you have 3 single phase pots (windings) wired in series or in parrallel depending on the config. A "wye " is 3 windings wired in parallel, and a "delta" is 3 pots (windings)wired in series. thats the just of it, until you get into 2 pot banks like an open delta secondary/open wye primary.
hardworkingstiff
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Power_Pig
Power_Pig
See posts 36 & 37 in this thread.
Power_Pig
POWER_PIG said:
See posts 36 & 37 in this thread.
mivey
Senior Member
There is no doubt in my mind that 3 wire 120/240 with a 180 degree displacement is single phase. I haven't seen anything posted that would make me think otherwise.
I had also always thought of 3 wire 120/208 with a 120 degree displacement as single phase. GE seems to be ok calling it single phase.
But now the quandry: the IEEE definition seems to indicate it is not 3 phase but they did not say what it was (maybe legs of a 3-phase?). The problem with the IEEE definition is that they use wishy-washy language like "it is intended to be so energized...".
This makes me question my previous stance on 3 wire 120/208 being single phase and I have not been able to reach a clear decision yet. Maybe it is something between a single phase and three phase but I did not have an IEEE definition for it. Maybe it only exists in another dimension and we tap into it using x-factor cables.
Does anybody have the IEEE dictionary? The definitions I had were from the IEEE transformer terminology publication.
I had also always thought of 3 wire 120/208 with a 120 degree displacement as single phase. GE seems to be ok calling it single phase.
But now the quandry: the IEEE definition seems to indicate it is not 3 phase but they did not say what it was (maybe legs of a 3-phase?). The problem with the IEEE definition is that they use wishy-washy language like "it is intended to be so energized...".
This makes me question my previous stance on 3 wire 120/208 being single phase and I have not been able to reach a clear decision yet. Maybe it is something between a single phase and three phase but I did not have an IEEE definition for it. Maybe it only exists in another dimension and we tap into it using x-factor cables.
Does anybody have the IEEE dictionary? The definitions I had were from the IEEE transformer terminology publication.
mivey
Senior Member
What do they call a 3-wire 120/208 service: single-phase, three-phase, portion-of-three phase, etc. I figure two-phase is out since this is not the old 90-degree two-phase (although it could be argued it really wasn't two-phase).
[edit: already have these (see post #36):
single-phase
two-phase
three phase
six-phase]
[edit: I kind of thought 3-phase would be out because we are missing a leg]
[edit: already have these (see post #36):
single-phase
two-phase
three phase
six-phase]
[edit: I kind of thought 3-phase would be out because we are missing a leg]
Last edited:
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
I believe the 120/208 (2 of 3 phases) does not meet the IEEE definitions of single-phase that Mivey posted.
I think it's just 2 of 3 phases, and not single-phase.
I think it's just 2 of 3 phases, and not single-phase.
mivey
Senior Member
It does seem to say single phase is zero or 180 degrees difference. It is just hard to tear away from being able to take a single phase load and hook it up to a single phase 120/240, then be able to take the same single-phase load and hook it up to three phase or I guess it is actually 2 of 3 phases. I do like the sound of "2 of 3 phases".hardworkingstiff said:
Something like: "You can operate some single phase loads by using 2 of the 3 phases although it will run different because...blah blah blah".
Rick Christopherson
Senior Member
I can't believe I didn't see this thread until today. :grin: Jeeze, I am bored.
How the heck can anyone justify calling a 120/208 system as single phase? It would be OK calling L1-L2/208 a single phase source, but as soon as you add the 120/208, this is no longer an option. Those three points are not colinear, and therefore cannot be single phase regardless how anyone chooses to define single phase. Three non-collinear points cannot be in phase with each other. Who in the world ever suggested that this was a single-phase system?
I have this piece of 3 foot long 4/0 cable that i would like to introduce to this person. In the immortal words of Al Pacino, "Say Hello to my little Friend!"
How the heck can anyone justify calling a 120/208 system as single phase? It would be OK calling L1-L2/208 a single phase source, but as soon as you add the 120/208, this is no longer an option. Those three points are not colinear, and therefore cannot be single phase regardless how anyone chooses to define single phase. Three non-collinear points cannot be in phase with each other. Who in the world ever suggested that this was a single-phase system?
I have this piece of 3 foot long 4/0 cable that i would like to introduce to this person. In the immortal words of Al Pacino, "Say Hello to my little Friend!"
quogueelectric
Senior Member
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- new york
Here it goes as far as In am concerned A 120/208 wye. a to b phase and to neutral from either hot Is 2 phase supply. How is this any different from a two phase old system that the 2 windings were 90* out of phase. These two windings are electrically 120* out of phase. I gotta go now I think I hear the doorbell.
crossman
Senior Member
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- Southeast Texas
We could build a 120/208 squirrel cage motor which used two of the phase conductors and the neutral. The stator would certainly create a rotating field much like that of the three phase squirrel cage motor stator. There would be no need of starting capacitors or shaded poles or start windings or any of that stuff like is required with single phase systems. So my thought is that 120/208 with two phase conductors and the neutral is not a single phase system.
quogueelectric
Senior Member
- Location
- new york
Probably more efficient than a 90* 2phase. And if you looked at the waveforms of A/N and B/N you would have two distinctive waveforms clearly out of phase with each other. Oh I think I gotta go now I have said enough.crossman said:
winnie
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- Springfield, MA, USA
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- Electric motor research
Rick Christopherson said:
This exact point gets debated over and over and over. See for example:
http://forums.mikeholt.com/showthread.php?t=82963
The point is that if you have a service supplied with two legs and the 'neutral' from 208/120 wye source, that has been _defined_ as a type of single phase service. Jim Dungar posted references to the standards organizations that created this definition; feel free to call them up and offer a visit from your friend
Clearly the physics of such a service is quite different from the physics of a single phase center tap service. For things such as calculating neutral current, developing a rotating magnetic field, or voltage zero crossing, such a service is clearly 'polyphase'.
But from a practical user standpoint, you have a panel with two ungrounded bus bars, you can use single pole or two pole breakers, you can serve only line-neutral or single phase line-line loads, etc.
While not perfectly descriptive of the physics, I am content to accept naming such a service 'single phase'.
-Jon
mivey
Senior Member
In reading this thread, I think it helped solidify my original thought that the 3-wire 120/208 is single phase. There were many good posts but I saved #54, #61, and #66 for future reference.winnie said:
The neutral was causing me a problem but Jim Dungar's posts helped me with that issue.
My delima started when I started looking at the following from the IEEE Publication "C57.12.80-2002 Standard Terminology for Power and Distribution Transformers": "it is intended to be so energized that, in steady state, the alternating voltages between any two terminals of entry have the same period and are in phase or in phase opposition."
With reference to the neutral the voltage at the two line conductor terminals are neither in phase or in phase oppositon. That made it sound like 120/208 3 wire could not be single phase.
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