- Location
- Massachusetts
kingpb 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.
Is it Single or Two Phase?
- Thread starter iwire
- Start date
- Status
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.
rick hart
Senior Member
- Location
- Dallas Texas
I would call it single phase since there is only a single zero crossing per common cycle- 1/60 of a second.
Two phase- if there ever was such a thing it was before I started paying attention to this website- would need to have two zero crossings per common cycle, just as 3 phase has 3.
That neutral does muddy up the water though, doesn't it?
Two phase- if there ever was such a thing it was before I started paying attention to this website- would need to have two zero crossings per common cycle, just as 3 phase has 3.
That neutral does muddy up the water though, doesn't it?
- Location
- Massachusetts
rick hart said:
It existed, it is still in the NEC, there is a two phase motor chart in 430.
Two Phase Info
charlie tuna
Senior Member
- Location
- Florida
two phase was originally two phases that were generated 180 degrees apart unlike the house power you are referencing that is 120 degrees apart which is two phases of a three phase system...................
120/240 residential service is in no way, shape or form, two phases. Phases have to do with timing, not polarity. Picture two 120V transformers in pure series, with the ground attached at the negative end of the second transformer. It would have 240V total across both to ground. I don't think anyone would think to call this "two-phase."
Why then the confusion when the ground is simply moved to between the two transformers in series? That's exactly what a center-tapped 240V transformer is. Did moving the ground magically create another phase? Certainly not.
As to "two phase motors," are you sure you're not referring to "split-phase" motors? I'm too young to have seen them, but some old-timers tell me about it frm time to time. Instead of the arrangement seen in 120/240, there was actually a 90 degree phase shift between two phases. This helped motors to start, i.e., it provides a true rotating magnetic field.
Why then the confusion when the ground is simply moved to between the two transformers in series? That's exactly what a center-tapped 240V transformer is. Did moving the ground magically create another phase? Certainly not.
As to "two phase motors," are you sure you're not referring to "split-phase" motors? I'm too young to have seen them, but some old-timers tell me about it frm time to time. Instead of the arrangement seen in 120/240, there was actually a 90 degree phase shift between two phases. This helped motors to start, i.e., it provides a true rotating magnetic field.
- Location
- Illinois
- Occupation
- retired electrician
Charlie,
Don
I though that two phase was 90 degrees out not 180.
Don
websparky
Senior Member
- Location
- Cleveland, Ohio
Single Phase
Single Phase
Single phase residential transformers are exactly that! In other words, they are a single coil transformer of 240V with a center tap that provides 120V.
Since this is alternating current, one end of the 240V coil is positive and the other end is negative and reverses every 1/30 of a second in relation to the center tap thus providing "two" phases when compared to the center tap.
Single Phase
Single phase residential transformers are exactly that! In other words, they are a single coil transformer of 240V with a center tap that provides 120V.
Since this is alternating current, one end of the 240V coil is positive and the other end is negative and reverses every 1/30 of a second in relation to the center tap thus providing "two" phases when compared to the center tap.
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websparky
Senior Member
- Location
- Cleveland, Ohio
240/120 Drawing
240/120 Drawing
Here is an example:
240/120 Drawing
Here is an example:
e57
Senior Member
- Location
- San Francisco, CA
Working on a house now that has TWO PHASE!
Me and the POCO guys were opening the christy at the street, and found out the area is served by a 3 phase center tapped delta. Why? I have no idea, but there it is. The two 120/240 legs serve the whole block.
Also many med/high rise will have 3 phase 208, and only use (Alternately) two phases to each resi unit.
Me and the POCO guys were opening the christy at the street, and found out the area is served by a 3 phase center tapped delta. Why? I have no idea, but there it is. The two 120/240 legs serve the whole block.
Also many med/high rise will have 3 phase 208, and only use (Alternately) two phases to each resi unit.
ty
Senior Member
- Location
- 3rd Rock from the Sun
Typically, our electricity is generated as a 3-phase system.
These 3 phases are transmitted all over the place.
The utility will try their best to balance the system by splitting off with one phase, then another, then another. Repeat.
So, for example, a pole-mounted transformer (pot) that feeds a residence will be fed by a single phase (of the 3-phase system) and from there it is stepped down.
I think the confusion with some people is that there are 2 'hot' wires at the house. These are 'legs' off the secondary side of the single-phase transformer.
These 3 phases are transmitted all over the place.
The utility will try their best to balance the system by splitting off with one phase, then another, then another. Repeat.
So, for example, a pole-mounted transformer (pot) that feeds a residence will be fed by a single phase (of the 3-phase system) and from there it is stepped down.
I think the confusion with some people is that there are 2 'hot' wires at the house. These are 'legs' off the secondary side of the single-phase transformer.
In my opinion, you can call it either.
I prefer to call it single phase just so one does not confuse it with the other 2 phase systems that have 4 wires or a phase shift other than 180 degrees.
Even better is to call it a "center tapped single phase".
However, I don't think there is anything wrong with calling it a 2 phase system. The question "Are the two line voltages in phase, or 180 degrees out of phase" all depends on what you use as the reference point. If you use the neutral as the reference point for both lines, they are out of phase. That is voltage A-N is out of phase with voltage B-N by 180 degrees. (Here I am using the common notation that voltage A-N is the voltage at point A with respect to point N). And, if you take Jim's reference to the IEEE, and use A-N and B-N as the voltages, they make their positive going crossings at different times. Therefore, you have two phases.
However, if you use the neutral as the reference for line A, and then use Line B as the reference for the neutral voltage, they are in phase and add together. That is, voltage A-N is in phase with voltage N-B. Here, the same IEEE reference, using the voltages A-N and N-B, they both make their positive going crossings at the same time. Therefore, it is single phase.
Conclusion- its both single and two phase depending on how you look at it.
I prefer to call it single phase just so one does not confuse it with the other 2 phase systems that have 4 wires or a phase shift other than 180 degrees.
Even better is to call it a "center tapped single phase".
However, I don't think there is anything wrong with calling it a 2 phase system. The question "Are the two line voltages in phase, or 180 degrees out of phase" all depends on what you use as the reference point. If you use the neutral as the reference point for both lines, they are out of phase. That is voltage A-N is out of phase with voltage B-N by 180 degrees. (Here I am using the common notation that voltage A-N is the voltage at point A with respect to point N). And, if you take Jim's reference to the IEEE, and use A-N and B-N as the voltages, they make their positive going crossings at different times. Therefore, you have two phases.
However, if you use the neutral as the reference for line A, and then use Line B as the reference for the neutral voltage, they are in phase and add together. That is, voltage A-N is in phase with voltage N-B. Here, the same IEEE reference, using the voltages A-N and N-B, they both make their positive going crossings at the same time. Therefore, it is single phase.
Conclusion- its both single and two phase depending on how you look at it.
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- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Dave, I'm not able to see your picture.websparky said:Here is an example:
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
So if your condo has two phases of a wye service lateral, do you have a 2-phase service in your residence?
websparky
Senior Member
- Location
- Cleveland, Ohio
Links to .JPG and .BMP
Links to .JPG and .BMP
Here are the links if you can not see the drawing:
http://grafixbynix.com/120TFR.jpg
and
http://grafixbynix.com/120TFR.bmp
Links to .JPG and .BMP
Here are the links if you can not see the drawing:
http://grafixbynix.com/120TFR.jpg
and
http://grafixbynix.com/120TFR.bmp
johnny watt
Member
Interesting topic [chuckle]
http://www.mikeholt.com/code_forum/showthread.php?t=76153
http://www.mikeholt.com/code_forum/showthread.php?t=76153
Agreed.iwire said:
For those that say it is two phase, have a look at the drawing in the attached pdf. For the purpose of discussion, the panels labeled with yellow text are identical. Note the number of transformer windings depicted for the three phase system...
View attachment 51
Minuteman
Senior Member
- Location
- The Sooner Nation
sceepe said:
Should you get too much of one you MAY see the other!
- Status