# Split Phase



## besc (May 16, 2010)

Okay. Be nice. What is split phase in residential lingo.:laughing:


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## 99cents (Aug 20, 2012)

Just a normal Edison three wire.


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## eddy current (Feb 28, 2009)

Ressi service. The transformer supplying power is single phase on the primary, and a center tapped single phase on the secondary. Or, split phase service


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## Big John (May 23, 2010)

When you have a single phase transformer you can put a neutral conductor in the middle of the winding.

This "splits" the single phase and gives you two totally independent hot legs to use for circuts.


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## besc (May 16, 2010)

Wow. That's it? Ive just never heard it called that. Just a basic 120/240 resi. Solar terminology likes to use that term a lot.


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## 99cents (Aug 20, 2012)

besc said:


> Wow. That's it? Ive just never heard it called that. Just a basic 120/240 resi. Solar terminology likes to use that term a lot.


That's it. Give this thread time, though. It will become overly technical and incomprehensible to the point where you should have asked your question at Plumber Talk.


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## MikeFL (Apr 16, 2016)

besc said:


> Wow. That's it? Ive just never heard it called that. Just a basic 120/240 resi. Solar terminology likes to use that term a lot.


And that is to discern from three phase or single phase that is not split phase.


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## matt1124 (Aug 23, 2011)

99cents said:


> That's it. Give this thread time, though. It will become overly technical and incomprehensible to the point where you should have asked your question at Plumber Talk.


Double phase. See attached photo.


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## backstay (Feb 3, 2011)

matt1124 said:


> Double phase. See attached photo.


How do you get a alternating waveform when you have positive and negative leads? Second question, how does a DC transformer function?


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## CheapCharlie (Feb 4, 2011)

Those should be polarity marks not +/- there is no such thing as a DC Transformer. 


Sent from my iPhone using Tapatalk


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## matt1124 (Aug 23, 2011)

backstay said:


> How do you get a alternating waveform when you have positive and negative leads? Second question, how does a DC transformer function?


I get an alternating waveform because of time. The winding diagram is a snapsnot of the cycle, the waveform would be over the course of one cycle. A DC transformer wouldn't be possible since there is no change of flux on a constant voltage.


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## matt1124 (Aug 23, 2011)

CheapCharlie said:


> Those should be polarity marks not +/- there is no such thing as a DC Transformer.
> 
> 
> Sent from my iPhone using Tapatalk


What symbols do _you _use to designate polarity?


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## matt1124 (Aug 23, 2011)

Does this help? The windings are a snapshot in time of one cycle. The waveform is only showing the A phase.


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## matt1124 (Aug 23, 2011)

Two phase. OF COURSE we just call it single phase residential.


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## backstay (Feb 3, 2011)

So you can make two phase out of a single phase system? I think there's a reason they call it "split" phase, and not two phase.


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## matt1124 (Aug 23, 2011)

backstay said:


> So you can make two phase out of a single phase system? I think there's a reason they call it "split" phase, and not two phase.


The way we tap it, you are splitting A SINGLE phase of what the power company supplies. If you were to look at leg A and leg B waveforms simultaneously on an oscilloscope, you would find them 180 degrees out of phase. 

On a meter, that's why one leg to ground is 120 but leg to leg it is 240. If it were actually ONE SINGLE PHASE twice on two lugs, you would read zero volts from leg A to leg B.

Theoretically you could take leg A from the house to your own experimental 1:1 center tapped transformer. You would take A SINGLE PHASE (leg A) to the primary and you would get 60 from terminal A to center on the transformer secondary, 60 from terminal B to center, and 120 from A to B.


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## Big John (May 23, 2010)

Legs A and B aren't different waveforms, they are opposite sides of the same waveform because they are the same phase. That's why they are 180° out: They have to be or else no voltage would exist across the winding.

Putting a center tap in there doesn't change how the coil functions, it just gives you another measurement point.


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## matt1124 (Aug 23, 2011)

John, we are saying the same thing. The only way to get "the other side" is to split the original waveform into two. You are in fact just changing the way you measure the original, but with the transformer you are technically deriving two phases.


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## matt1124 (Aug 23, 2011)

If we used a 480 primary:240/120 seconday single phase transformer would you consider that two phase?


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## matt1124 (Aug 23, 2011)

I'm on my phone so I can't edit. Please note the previous post, I am implying we would feed that transformer from two of the available three phases of 480


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## LGLS (Nov 10, 2007)

matt1124 said:


> Double phase. See attached photo.


"POCO 100 BILLION volts?!" :laughing:


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## LGLS (Nov 10, 2007)

I notice in some areas it seems the residential 120/240 transformer is tapped off of 2 phases, instead of one single phase and ground.Or am I not seeing things right?


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## PlugsAndLights (Jan 19, 2016)

matt1124 said:


> Double phase. See attached photo.


How come the first half of the wave is called A and the second half B?:jester:
P&L


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## backstay (Feb 3, 2011)

matt1124 said:


> I'm on my phone so I can't edit. Please note the previous post, I am implying we would feed that transformer from two of the available three phases of 480


No, I don't think you are getting a multiple phase out of your single phase transformer. If you were, you wouldn't need capacitors to mimic two phases in the start windings of your single phase motors. If what you say is true, all 240 volt motors would start and run without them.


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## matt1124 (Aug 23, 2011)

P&L, because I'm a doofus. It goes over to the left!


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## Big John (May 23, 2010)

matt1124 said:


> If we used a 480 primary:240/120 seconday single phase transformer would you consider that two phase?


 It's single phase because it uses a single winding.

It could be fed by two phases or L-N but that doesn't change the single phase output.


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## HackWork (Oct 2, 2009)

Go to Philly if you want to see 2 phase.


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## hardworkingstiff (Jan 22, 2007)




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## hardworkingstiff (Jan 22, 2007)

*For those that don't know*

https://en.wikipedia.org/wiki/Two-phase_electric_power


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## Signal1 (Feb 10, 2016)

99cents said:


> That's it. Give this thread time, though. It will become overly technical and incomprehensible to the point where you should have asked your question at Plumber Talk.


Nailed that.


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## matt1124 (Aug 23, 2011)

Big John said:


> It's single phase because it uses a single winding.
> 
> It could be fed by two phases or L-N but that doesn't change the single phase output.


So the number of windings used on the primary side to reach whatever service we end up with would be the count of the phases, regardless of the winding count on the secondary side?

One winding connected to one phase of POCO -> Single phase
Three windings connected to three phases from POCO -> Three phase

Correct?


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## Ultrafault (Dec 16, 2012)

The wave is most defiantly not 2 phase matt. Read the wiki article on split phase power. Then read allaboutcircuits.com alternating current chapter ten. All you would be doing is refrencing the single waveform at two diffrent points. 
Your transformer diagram you drew would have phasors for both readings at 0 degrees. Were the polarity on the left reversed as it would be seen from an o scope you would see one phasor at 0 degrees the other at 180. The circuit has not changed at all but the instrument is telling you something different. Remember we must be smarter than our tools.


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## matt1124 (Aug 23, 2011)

Ultrafault said:


> The wave is most defiantly not 2 phase matt. Read the wiki article on split phase power. Then read allaboutcircuits.com alternating current chapter ten. All you would be doing is refrencing the single waveform at two diffrent points.
> Your transformer diagram you drew would have phasors for both readings at 0 degrees. Were the polarity on the left reversed as it would be seen from an o scope you would see one phasor at 0 degrees the other at 180. The circuit has not changed at all but the instrument is telling you something different. Remember we must be smarter than our tools.


So two sources, in phase with each other, but with a relative phase shift of 180 degrees between? Not flipped over the x-axis, but actually just shifted over ALONG the x-axis?


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## Ultrafault (Dec 16, 2012)

It is a single waveform the difference comes from where you place your probes. Boost configuration is the one you were trying to describe. I don't know if the buck configuration is used but I like to draw.


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## matt1124 (Aug 23, 2011)

Ultrafault said:


> It is a single waveform the difference comes from where you place your probes. Boost configuration is the one you were trying to describe. I don't know if the buck configuration is used but I like to draw.


In a buck configuration, is it still a single waveform?


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## CheapCharlie (Feb 4, 2011)

matt1124 said:


> What symbols do _you _use to designate polarity?




A dot like this picture









Sent from my iPhone using Tapatalk


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## matt1124 (Aug 23, 2011)

CheapCharlie said:


> A dot like this picture
> View attachment 99481
> 
> 
> ...


Neat! Never learned it that way


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## matt1124 (Aug 23, 2011)

Been reading a bit... starting to make sense I think. Mathematically they are out of phase, practically they are not since the phasors lie on the same plane. Am I on the right page here guys?


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## 99cents (Aug 20, 2012)

Technically, your power should only work on Mondays, Wednesdays and Fridays.


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## backstay (Feb 3, 2011)

My power is photo coupled to God, so it works 6 days a week.


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## Ultrafault (Dec 16, 2012)

matt1124 said:


> Been reading a bit... starting to make sense I think. Mathematically they are out of phase, practically they are not since the phasors lie on the same plane. Am I on the right page here guys?


Exactly.


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## RePhase277 (Feb 5, 2008)

If you ground your oscilloscope to the neutral and connect channel 1 to one leg and channel 2 to the other leg, the two waveforms on the screen will be 180 degrees apart. That doesn't mean that they are two different phases. That just means you are measuring opposite ends of the same phase relative to the center point.


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## inetdog (Apr 13, 2016)

matt1124 said:


> Been reading a bit... starting to make sense I think. Mathematically they are out of phase, practically they are not since the phasors lie on the same plane. Am I on the right page here guys?


Fundamentally, if you have two sine waves which are 180 degrees out of phase you cannot derive a sine wave of any other phase angle from them.
If you have two sine waves offset by 120 degrees you can easily derive the third, with phase 240 degrees.
Or any other phase angle you want as long as it is related to the first by the ratio of two integers. 
Same thing if you have two sine waves offset by only 90 degrees (two phase).


mobile


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## brian john (Mar 11, 2007)

matt1124 said:


> John, we are saying the same thing. The only way to get "the other side" is to split the original waveform into two. You are in fact just changing the way you measure the original, but with the transformer you are technically deriving two phases.


Two phase is a totally different distribution system hardly ever used these days distribution system.

2-Phase 5-wire.


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## brian john (Mar 11, 2007)

HackWork said:


> Go to Philly if you want to see 2 phase.


Only place I ever saw it.


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## drsparky (Nov 13, 2008)

I think Tesla's power generation at Niagara Falls in the late 1900s was two phase.


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## Big John (May 23, 2010)

We have some customers that still use it. Entire plants set up 100 years ago as 2 phase, so it's cheaper to keep that distribution than reebuild the plant.


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## hardworkingstiff (Jan 22, 2007)

backstay said:


> My power is photo coupled to God, so it works 6 days a week.


:smile:


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## matt1124 (Aug 23, 2011)

inetdog said:


> Fundamentally, if you have two sine waves which are 180 degrees out of phase you cannot derive a sine wave of any other phase angle from them.
> If you have two sine waves offset by 120 degrees you can easily derive the third, with phase 240 degrees.
> Or any other phase angle you want as long as it is related to the first by the ratio of two integers.
> Same thing if you have two sine waves offset by only 90 degrees (two phase).
> ...


Can you give more detail on this please? I know how they come up with high-leg 120/240 3 phase as far as connections and the basics of what is happening, but thinking about what all we've talked about here, how is this derivation accomplished?


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## RePhase277 (Feb 5, 2008)

matt1124 said:


> Can you give more detail on this please? I know how they come up with high-leg 120/240 3 phase as far as connections and the basics of what is happening, but thinking about what all we've talked about here, how is this derivation accomplished?


By using an inductor or capacitor to cause a phase shift. For example, a single phase induction motor is really a 2-phase induction motor. A second winding is powered through a capacitor. This capacitor causes the current to be 90 degrees out of phase with the current in the other winding, giving rise to the rotating field. Once the motor is turning, the circuit for the second winding is opened, hut the motor continues to rotate because of the inductive effects the rotor experiences while moving through the field.


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## telsa (May 22, 2015)

Big John said:


> We have some customers that still use it. Entire plants set up 100 years ago as 2 phase, so it's cheaper to keep that distribution than rebuild the plant.


Cue Scott-Tee Transformers.

BTW, on the history, they were set up for Edison's DC scheme.

When everyone realized that Tesla//Westinghouse's scheme was the hands down winner, the original Edison adopters went over to two-phase... and then pitched Scott-Tee transformers.

It was a win-win-win -- as lighting loads didn't need three-phases.

[ They were a tad short on electricians and wire back then, too. ]

{ Once they jumped away from DC, the voltages available exploded upward. That was double-plus good. Edison's scheme was a copper hog. }


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## lightman (Oct 14, 2015)

Just a couple of things to add about transformers.

The polarity of a transformer is either additive or subtractive and refers to the relative direction of the induced voltage between the high voltage terminals and the low voltage terminals. Not really important unless you are banking them or changing them out hot. 

A high leg is the result of grounding the center of the winding in one transformer of a Delta bank. This is usually to get a single phase voltage in addition to a 3 phase voltage. The high leg voltage will equal 1.73 times the secondary name plate voltage. It will also be the bushings that are furtherest from the grounded bushing.

Whether the transformers high voltage side is connected to one phase or two depends on the name plate voltage. Some utilities run 2 phases to larger transformers as a way to balance the load on the line or to reduce the load that would be on a single line. This is really not a 2 phase system, just 2 phases used from a 3 phase system.

Prolly more than most want to know about transformers!


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## matt1124 (Aug 23, 2011)

Is there an additional inductor installed or is it inherent in the windings of the transformers? If it is a phase shift, what will the phasors look like?


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## RePhase277 (Feb 5, 2008)

matt1124 said:


> Is there an additional inductor installed or is it inherent in the windings of the transformers? If it is a phase shift, what will the phasors look like?


What specific applocations are you thinking of? I don't get the question.


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## matt1124 (Aug 23, 2011)

RePhase277 said:


> What specific applocations are you thinking of? I don't get the question.


I know we are in residential, but I am talking about open delta 120/240 three phase.

Is that not a split phase transformer with an additional transformer, or is it a special transformer, with a center tap, with another transformer, along with some type of additional inductor/capacitor to create a phase shift? I know open delta is not symmetrical, but what is the difference in this center grounded transformer than the one at my home?


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## RePhase277 (Feb 5, 2008)

It's fed with 3-phase on the primary. So 3-phase comes out.


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## hardworkingstiff (Jan 22, 2007)

RePhase277 said:


> It's fed with 3-phase on the primary. So 3-phase comes out.


Isn't it interesting that when we feed 2 phases and a neutral to a residence, we say it's a single-phase service, but that picture shows those two transformers being fed with 2 phases and a neutral and it's called being fed with 3-phase. 

I've always thought it was wrong to say 2-phases of a wye and a neutral is single-phase.


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## RePhase277 (Feb 5, 2008)

hardworkingstiff said:


> Isn't it interesting that when we feed 2 phases and a neutral to a residence, we say it's a single-phase service, but that picture shows those two transformers being fed with 2 phases and a neutral and it's called being fed with 3-phase.
> 
> I've always thought it was wrong to say 2-phases of a wye and a neutral is single-phase.


I didn't notice the middle wire lacking a fuse. 

What would we call it? I know what you're saying. It isn't 2-phase because a system exists with that name. And it isn't really 3-phase, even though you could get 3-phase out of it. I think the voltage relationship precludes it from being called xx-phase. And it's use is always for single phase loads. I don't know what it should be called.


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## matt1124 (Aug 23, 2011)

RePhase277 said:


> I didn't notice the middle wire lacking a fuse.
> 
> What would we call it? I know what you're saying. It isn't 2-phase because a system exists with that name. And it isn't really 3-phase, even though you could get 3-phase out of it. I think the voltage relationship precludes it from being called xx-phase. And it's use is always for single phase loads. I don't know what it should be called.


Let's call it double phase :jester:


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## lightman (Oct 14, 2015)

The picture that Matt posted is of an open delta bank. Its considered 3 phase because you have 3 phase on the secondary side. Both transformers are just normal transformers, nothing special and no capacitors. Transformers come with a grounding strap on the middle bushing. When wiring a bank like this you remove the ground strap on the 2nd transformer. You will have one bushing on each transformer tied together, usually the closest two. The bushing furtherest from the neutral will be the high leg. This type of bank is for light commercial use where you have mostly single phase load and little 3 phase load. As someone else stated, you don't get the rated capacity from a bank of this type.


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## matt1124 (Aug 23, 2011)

Lightman, how is the primary side connected to each phase or neutral coming from the power company?


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## matt1124 (Aug 23, 2011)

Is this correct?


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## lightman (Oct 14, 2015)

It depends on the name plate voltage on the transformer. In my area the primary voltage is 7620 phase to ground and 13800 phase to phase. If the name plate says 7620/240-120, it would look like your top picture. If the name plate says 13800/240-120 we would use all 3 switches. The outside switch would connect to the outside bushing, the middle switch would connect to both of the inside bushings and the other outside switch would connect to the other outside bushing. Three phases and three switches is preferable because it keeps the load on the system balanced better. Always a problem! Our company actually quit buying transformers with two primary bushings if they only required single phase on the primary side. Your picture would depict a 7620 primary transformer.

Looking at the secondary connections on your top picture, the ground strap on the middle bushing of the right hand transformer would be removed. The lead on the far right will be the high leg.

You would only wire a bank like your second picture if the transformers were different polarity. That info is on the name plate also.

I can wire transformer banks but I need help posting pictures on the internet! Go figger!


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## matt1124 (Aug 23, 2011)

Using the 7620/240-120 transformers in an open delta configuration:

So how does the addition of the second transformer with the UNGROUNDED center bushing cause the first transformer with the GROUNDED center bushing to supply two of three phases? Is this not the same split-phase transformer we use on a house that can only supply one phase?


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## lightman (Oct 14, 2015)

Yes, its the same type transformer with the ground strap removed from the middle bushing. The first transformer with the grounded bushing supplies 120 volts, 120 volts and then 240 volts phase to phase because the winding is grounded at its midpoint. By connecting the inside bushing of the first transformer to the inside bushing of the 2nd transformer you are just extending that winding and the far end of that winding supplies the 3 phase.

I wish I knew how to draw this out on computer.


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