# Why Is American 220v Not Considered 2 Phase?



## Superburban

A little thing that has always been bugging me. Here we have 220 volts by using 2 110 volt legs that are 180 degrees apart. Ie, load on 2 legs. 

Much of Europe has 220 volts, but only on one leg, the other is neutral. Like our 110V setup, but 220 volts.

3 phase has power on three wires, makes sense to call it 3 phase.

Single phase 110V here  (or 220V in much of Europe), only has the load on one wire. Again, it makes sense to call in single phase.
Following all that, it seems that our 220 Volts (110 on each leg), should be called 2 phase.


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## JimDawson

Two phase has a phase difference of 90° rather than 180°


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## Tony Wells

It's single phase because it comes off one winding in the transformer. We just center tap it to get the 120. 3 phase comes from 3 separate windings on the secondary of the transformer.


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## Superburban

Ok, Thanks that makes sense. Is there any place that uses 2 phase?

Another similar question, how do they get the two legs in phase, when the power being generated is in 3 phase, and has the legs 120 degrees apart?

Thanks for the quick reply, and illustrations, they help.


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## Superburban

Tony Wells said:


> It's single phase because it comes off one winding in the transformer. We just center tap it to get the 120. 3 phase comes from 3 separate windings on the secondary of the transformer.



I get it now, so residential only gets one leg from the power station, and it is converted to two hot legs at the transformer. I always thought residential got two legs out of the three phase.

Thanks


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## Tony Wells

No, the primary feed to the transformer on the pole (at least mine) is 7200 VAC, single phase. There is one hot wire and a neutral run to it, with the neutral also being grounded by a copper wire running down the pole to a round plate on the bottom of the pole. So mos residential services, on my rural coop, run a simple 2 winding transformer, although I should mention that on the secondary, there are I believe 3 hot taps, so they can get the proper or closest voltage out on the secondary. This allows for some variation in the primary feed. It could be that one of the possible secondary taps runs at 260, one close to 240 (mine is close to 237), and one could be 190. So when they bring the service drop in, they make the best selection then.

If you look at the poles, some will have 3 hots on the top crossbar. That is all three phases. But in residential areas, normally you won't see all three, but often 2, so they have twice the capacity since they can use either one, whichever is loaded least, to add the next customer. But that represents 2 separate windings in a transformer upstream. So they are both full wave, single phase.


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## rwm

This came up before and someone said 2 phase was available in Philly?

R


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## Tony Wells

Yes, 2 phase is still in limited use. Wiki lists parts of Pensilvania as well as part of Connecticut as still using it. I think part of the confusion is that true 2 phase requires 4 conductors, 2 for each phase, whereas single phase is delivered with only 2, a hot and a neutral.

I think there is kind of a crossover in descriptive terms. When we have a center tapped transformer, we can properly call it "split phase", because half the winding provides "phase A" and the other half "phase B", so it's technically proper to call it "dual phase"or "split phase". Easy transition to "2 phase", but truly a little different animal. When you split a single phase, which contains the entire sine wave of a "phase", you only get either the voltage swing from zero to positive, with the peak of the sine wave at whatever voltage half the whole winding is providing, in our case here in the US, that's about 120VAC. Or, you could get the "other" half of the sine wave, which swings from zero to the "negative" peak, which reaches the same voltage as the other half. They are symmetrical. Then enter the time domain. There is a period on split single phase during which the voltage is zero. That's while the power swings to the other side of zero. So that pair of wires just waits while the other gets the other half of the sine wave.  Think of zero being represented by the neutral wire. It's always at zero potential. Then all our comparisons reference that neutral as the mid-point of our entire phase cycle.  So half the time each "hot" leg of our single phase system is at zero volts while the other leg gets the other peak and hence is hot. Then when you are using 240, and not using the neutral as a reference zero, there is only an infinitely small time when the voltage drops down the sine wave and _crosses]_ the zero voltage line, but various factors make this "zero crossing" insignificant for most applications, like motors for instance. Then you properly measure the available voltage from "peak to peak" or "P-P". The reasons behind this are a little complicated, and I don't know enough about them to truly provide a good explanation.

Now, all the real electrical engineers can come in and clear up any details I have gotten wrong, or shoot the whole things down. If  I have a gross misunderstanding of the subject, I hope they do. I'm sure they could at least add something, or maybe give a better explanation, but that's how I have it in my mind, anyway, for what that's worth .


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## CluelessNewB

Personally I think waveform diagrams like Jim Dawsons 240/120 although technically correct are maybe adding to the confusion.  Typically 240 V motors have no connection to the neutral.  Since the motor only has 2 connections if we were to arbitrarily choose one leg to call our zero volt reference, the waveform will look like a sine wave and except for the amplitude would be identical to what you would see on a 120V line.  Voltage is relative and is always measured between two points, just like distance.  To show a signal on a oscilloscope that looked like that diagram would require 3 connections (and an oscilloscope with multiple channels) because you would really be measuring 2 voltage signals referenced to neutral.   Note that the motor itself only has 2 connections and only "sees" one voltage signal and that signal looks like a sine wave.  

I have either made this clearer or totally muddied the waters, I'm not sure which


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## Keith Foor

Well, to further complicate matters I have heard US power referred to as Edison 2 phase.  
Now that makes little to no sense since Edison HATED AC and wanted DC in everyone's house with a small generator in a barn out back.
Tesla and Westinghouse partnered to create the system we all know today in the US so how Edison got involved is anyone's guess and may be totally incorrect.  But I have heard that said a couple times referring to the 2 leg 180 degree out of phase 120/240 60Hz system we currently enjoy.


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## Keith Foor

Tony Wells said:


> It's single phase because it comes off one winding in the transformer. We just center tap it to get the 120. 3 phase comes from 3 separate windings on the secondary of the transformer.




Well, it's generated as 3 phase at the power plant.


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## John Hasler

rwm said:


> This came up before and someone said 2 phase was available in Philly?
> 
> R


Yes.  Just to add to the confusion it is possible to convert between 3 phase and 2 phase with a device called a Scott T transformer.
https://en.wikipedia.org/wiki/Scott-T_transformer


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## Tony Wells

Yes it is, Keith, and the generators have 3 winding sets to do it. That's how we have 3 separate waveforms  and there are 3 hots to the one neutral. The transmission transformers are generally separate, per phase, because of size. That way they are simpler and cheaper to build also.

When it get to the distribution stations and sub stations it's still 3 phase, all the way out into the fields, where it is divided up by selection of conductors needed and stepped down to the voltage needed. It still only take one hot and one neutral to provide a single secondary winding that is center tapped to give household 120/140. Pole pigs may well have more than one secondary winding if they are serving more than one business or residence. But even those transformers are fed generally with a single primary hot. In fact they could stack on secondaries until they run out of amperage, but they would always be single phase like the primary.

I could accept using the term split-phase for what we have, since the 120 outlets really only receive half-wave AC. That seems fair to me because it's half of the complete sine wave that we see on our 240. But I don't recall anyone calling it that.


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## CluelessNewB

Tony Wells said:


> I could accept using the term split-phase for what we have, since the 120 outlets really only receive half-wave AC. That seems fair to me because it's half of the complete sine wave that we see on our 240. But I don't recall anyone calling it that.



Actually if you were to put an *oscilloscope probe on a 120 outlet you would still see a full sine wave, the shape would not be changed, just it's amplitude (and peak-peak voltage) would be 1/2 the height of the 240V.   I wish I still had an oscope available so I could take some pictures.  




* Caution most oscilloscopes can't handle that high of an input voltage without using a 100x probe!


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## Bill Gruby

2 Phase is still in limited use in Hartford Ct.

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

 "Billy G"


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## John Hasler

CluelessNewB said:


> Actually if you were to put an *oscilloscope probe on a 120 outlet you would still see a full sine wave, the shape would not be changed, just it's amplitude (and peak-peak voltage) would be 1/2 the height of the 240V.   I wish I still had an oscope available so I could take some pictures.


This is quite correct.

. ...........____ . . . _____________ L1
. ................... ) ||  (
. 7200 ......... ) ||  (          120
. ................... ) ||  (______________NEUTRAL
. ................... ) ||  (                                                
. ................... ) ||  (           120                               
. .............___) ||  (_____________ L2


(The dots are to fight off HTML space compression)

You can think of the center-tapped secondary as two separate 120V windings connected in series.  Each gives half the total voltage, not half the waveform.


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## abrace

Tony Wells said:


> I could accept using the term split-phase for what we have



It is commonly referred to as 240V split single phase around here.

The multi wire branch circuit 'exploits' this fact, which is what allows us to have (2) 120V circuits share a single neutral provided they are on separate poles. I use that all the time. Want a pair of 20A circuits in the shop? You can run 12-3 to them and split off the hots when you get into the double gang box. One hot to one receptacle, the other to the other, and share the neutral. The neutral won't ever get overloaded as it only carries the difference in load between the 2 circuits. One receptacle pulling 5 amps, and the other is pulling 7, there is only a 2A load on the neutral.

This was a lot more commonly done before the arc fault invention.


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## rwm

I'm not buying that explanation. Someone go put a scope on the 7200 v line and see what the wave form is there.....
R


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## dieselshadow

rwm said:


> I'm not buying that explanation. Someone go put a scope on the 7200 v line and see what the wave form is there.....
> R



It would be identical. Transformers cannot change the sine wave.


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## John Hasler

Superburban said:


> I get it now, so residential only gets one leg from the power station, and it is converted to two hot legs at the transformer. I always thought residential got two legs out of the three phase.
> 
> Thanks


That's actually one way to do it: you get 208 phase to phase and 120 phase to neutral.  It isn't common in residental distribution but you will find it in some large buildings such as hospitals.  In residential distribution they normally just connect the primary of your pole pig phase to neutral (with adjacent pole pigs going on different phases to balance the load).  If you are out near the end of a branch like we are there may only be one phase up on the poles.


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## Tony Wells

Yup, you guys are spot on. That's what I get for post at 1 in the morning. My apologies for any confusion.


Oh, and unless you have an isolation transformer, or your scope is so coupled internally, best not to probe the socket your scope is plugged into. Or use a battery operated portable scope. So I've heard.....never smoked a scope yet.


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## GA Gyro

Hmmm...
Letting the magic smoke out of a scope...
Would be a real mistake... 
Much worse than letting the smoke out of a sawzall or a drill...


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## rwm

I hope ya'll know that was a joke about measuring the 7200 V lines! 
Actually we live in a neighborhood built in 1920 and we have tons of overhead high voltage lines just waiting to break. Last year I had to call about a tree on fire from arcing. Fortunately the rain put it out 'cause they showed up the next day to check it out. Good ole Duke Power.
R


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## olduhfguy

It's easy to see that 3 wires could be considered 3-phase but it's a US problem. Most countries that provide only 240 volts have 2 service wires, but if they had 3 service wires it would most likely be 3 phase. In the US we couldn't decide whether we liked 120 or 240 volts so we decided to have both -  we have one phase and 3 wires (120v to neutral, 240v between L1 and L2 - the third one is a neutral/ground). To confuse things further if you order 3 phase in the US you may get grounded delta 3 phase with one leg neutral/grounded, 3 phase delta with all phases above neutral, or 3 phase wye all phases above neutral.


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## GA Gyro

rwm said:


> I hope ya'll know that was a joke about measuring the 7200 V lines!
> Actually we live in a neighborhood built in 1920 and we have tons of overhead high voltage lines just waiting to break. Last year I had to call about a tree on fire from arcing. Fortunately the rain put it out 'cause they showed up the next day to check it out. Good ole Duke Power.
> R



Yeah... Definitely not a good idea to climb the pole to measure voltage...
As I understand it... it is a federal offense (terrorism) for an un-authorized person to climb a utility poll...

About a year or so ago... they changed the Xformers in my neighborhood... was chatting with the line guys...
They said the current service 'was' 8700 volts, however it was gonna change to 12K volts.  
There is 3 phase at the head of my subdivision on the boulevard... none in the neighborhood.  
Surprising... one leg (one line) serves close to 100 homes.


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## Superburban

Ahh man, I really wanted to check out the high voltage lines. I downloaded the oscilloscope app for my I phone, and duct tapped my 20 foot aluminum ladder to the end of my 30 foot aluminum ladder. I figured with the light rain we are having, no one would see me climb up a,d check out the wave forms.

Ohh well, I'll just drink another beer instead.


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## Keith Foor

OK, some additional info on 3 and split phase.  208 3 phase is 208 and NOT 240 because the phases are not 180 degrees out of phase.  Since the phases are 120 degrees out of phase the maximum leg to leg RMS voltage is 208.  RMS is something else.  Since we have now drug o-scopes into this discussion.  The actual PEAK voltage to neutral is actually 169 volts and not 120.  120 is the RMS voltage that what was adopted to refer to it.  Did you ever wonder why you needed to use 370 volt caps for a RPC?  That would be it.  the Peak voltage on 240 is actually  338 volts.  So while a regular volt meter will show 240 a scope which shows peak voltage would indicate 338 volts.  

More confusion


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## ddickey

Keith Foor said:


> OK, some additional info on 3 and split phase.  208 3 phase is 208 and NOT 240 because the phases are not 180 degrees out of phase.  Since the phases are 120 degrees out of phase the maximum leg to leg RMS voltage is 208.  RMS is something else.  Since we have now drug o-scopes into this discussion.  The actual PEAK voltage to neutral is actually 169 volts and not 120.  120 is the RMS voltage that what was adopted to refer to it.  Did you ever wonder why you needed to use 370 volt caps for a RPC?  That would be it.  the Peak voltage on 240 is actually  338 volts.  So while a regular volt meter will show 240 a scope which shows peak voltage would indicate 338 volts.
> 
> More confusion


Not quite, or maybe I don't understand what you're saying. 208 three phase will always be a wye connected secondary with 120v phase to ground. If the voltages are the difference of 1.73 (√3) they are always wye connected. 240/120 is always delta connected as it is 1/2 ratio. phase to phase is 240 and phase to ground is 120, it's a 4 wire system. Phase angles are 120° apart in all instances. RMS has nothing to do with 208v systems.


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## Eddyde

John Hasler said:


> That's actually one way to do it: you get 208 phase to phase and 120 phase to neutral.  It isn't common in residental distribution but you will find it in some large buildings such as hospitals.  In residential distribution they normally just connect the primary of your pole pig phase to neutral (with adjacent pole pigs going on different phases to balance the load).  If you are out near the end of a branch like we are there may only be one phase up on the poles.


Here in NYC its not uncommon for residential buildings to have 3 phase service, especially new or renovated buildings. The main reason is for elevators and air conditioning. However, most apartments will only have a single phase (two of the three phases) sub panel. 208v phase to phase 120v to the neutral.


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## John Hasler

Eddyde said:


> Here in NYC its not uncommon for residential buildings to have 3 phase service, especially new or renovated buildings. The main reason is for elevators and air conditioning. However, most apartments will only have a single phase (two of the three phases) sub panel. 208v phase to phase 120v to the neutral.


By residential I meant single-family.


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## Eddyde

Yes thats true for most areas of the country. Here even 1-2 family homes that have single phase service are getting two of three phases from the street, not split phase.


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## Keith Foor

ddickey said:


> Not quite, or maybe I don't understand what you're saying. 208 three phase will always be a wye connected secondary with 120v phase to ground. If the voltages are the difference of 1.73 (√3) they are always wye connected. 240/120 is always delta connected as it is 1/2 ratio. phase to phase is 240 and phase to ground is 120, it's a 4 wire system. Phase angles are 120° apart in all instances. RMS has nothing to do with 208v systems.




Well, I have to get sort of technical here, so ask questions if this gets really confusing.  208 3 phase is 3 legs of 120 volts to neutral that are 120 degrees apart.  Split phase or standard residential wiring is 2 legs of 120 that are 180 degrees apart.  The reason that its not 240 3 phase is the phase angle difference.  the 120 volts is the maximum plus and minus voltage that is referenced to neutral.  Now becasue the 240 is 180 degrees out of phase as one leg hits the peak positive voltage, the other leg is reaching it's maximum negative voltage.  The difference between the two legs at that point is 240 volts.  Because 3 phase is 120 and not 180 degrees apart, only one leg at a time reaches it's max voltage.  The 208 is the difference between the two legs at the point of maximum voltage of only one leg and a reduced voltage of the other leg because it's not at its maximum voltage at that same time.

The whole RMS vs Peak is another discussion.


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## ddickey

Keith Foor said:


> Well, I have to get sort of technical here, so ask questions if this gets really confusing.  208 3 phase is 3 legs of 120 volts to neutral that are 120 degrees apart.


Agree, this is found in a wye connected secondary. 





Keith Foor said:


> Split phase or standard residential wiring is 2 legs of 120 that are 180 degrees apart.


It is one 240V leg center tap split . There is no phase shift just opposite polarities.  Same reason why it is not called two phase.





Keith Foor said:


> The reason that its not 240 3 phase is the phase angle difference.  the 120 volts is the maximum plus and minus voltage that is referenced to neutral.  Now becasue the 240 is 180 degrees out of phase as one leg hits the peak positive voltage, the other leg is reaching it's maximum negative voltage.  The difference between the two legs at that point is 240 volts.  Because 3 phase is 120 and not 180 degrees apart, only one leg at a time reaches it's max voltage.  The 208 is the difference between the two legs at the point of maximum voltage of only one leg and a reduced voltage of the other leg because it's not at its maximum voltage at that same time.


√240²-120²=208 We don't even use the 208v on a delta secondary, do we? 208 is derived from one leg (240v) and the center tap (120v).



Keith Foor said:


> The whole RMS vs Peak is another discussion.


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## jim18655

Ahh... 240v delta - probably responsible for burning up more equipment than any other voltage known to electricians.


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## Tony Wells

OK, now I've got a question. Probably staring me in the face, but atm, I can't see the answer. Might be the cold medicine. Since our secondary is a center tapped 240 volt winding, and we derive our 120V from basically what amounts to 2 windings secondary to the same primary (or are they?), how is is that they are out of phase 180° to get the 240V? Or is it that each 120V sine wave is _above_ and _below_ the neutral in entirety? How can that be? It would appear to me that they (the sine waves of 120V) should run in exactly the same time domain, and would operate more like parallel secondaries. If I think about it a while, I might realize how simple the answer is, but right now it's not coming to me. So someone 'splain it to me please.


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## jim18655

Neutral isn't a voltage in relation to the other two hot legs, it is the center of the winding. If you consider the whole secondary as an autotransformer then as the winding ratio increases the voltage between the  two legs will increase. The center tap - our usually grounded conductor - will be 120v to the bottom leg. The top leg - the other hot - will be  240v to the bottom hot leg with a 120v difference to the center tap. The phase of the sine wave is dependent on the magnetic flux "moving" in the core and transferring energy into the secondary. Think of the output legs pushing and pulling in sync with each other. This is why there are phasing dots shown on schematics when you have transformer coils to wind.  If you could flip the connections in the secondary so that the phasing of the core is the same you would have parallel 120v connections without a 240v connection. Think of a buck-boost transformer connection where the polarity is additive or subtractive. 

Here's one to think about - assume the power company didn't ground the center tap or you have a 480 to 120/240 transformer. You could ground either "hot" leg and connect it to the neutral bar in a panel. Center tap to the main breaker and the other "hot" leg to the main. Nothing would trip out and depending which phase you used it would give you 120v to neutral bar, 240v to the neutral bar and 120v between phases on a 2 pole breaker with no difference in shock hazard than in a properly connected panel. We only get shocked or sparks between hot and ground because of the ground connection we establish when we install the panel allows a complete circuit back to the transformer.


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## Tony Wells

As I suspected, now with a clear head (sorta) I see it as no longer 2 separate windings in a secondary, but a single winding with the appropriate turns ratio to give the 240V. Grounding the center tap is immaterial to getting the 240V, but is part of how we use 240V safely.

Thanks Jim.


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## markba633csi

I'm wondering, (and I should know this) if, in the case of a motor wired for 220 volt,  the connection point of the two run windings could be tied to neutral to stabilise the voltage that appears there and reduce the voltage spike/swing impressed on the start cap. The start winding, cap and centrifugal switch are usually across one of the run windings, and I bet the midpoint of the run windings thrashes around quite a bit when starting and stopping.  Anybody?
Mark S.


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## John Hasler

markba633csi said:


> I'm wondering, (and I should know this) if, in the case of a motor wired for 220 volt,  the connection point of the two run windings could be tied to neutral to stabilise the voltage that appears there and reduce the voltage spike/swing impressed on the start cap. The start winding, cap and centrifugal switch are usually across one of the run windings, and I bet the midpoint of the run windings thrashes around quite a bit when starting and stopping.  Anybody?
> Mark S.


The motor wouldn't start.   Each winding would be connected directly across 120VAC and and neither would be subjected to any phase shift.  The capacitor would draw lots of current but it would not affect the motor.

Look at how a 120V capacitor-start motor is wired.  The capacitor actually achieves its effect by being in *series* with one winding.


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## MikeWi

Keith Foor said:


> Well, to further complicate matters I have heard US power referred to as Edison 2 phase.
> Now that makes little to no sense since Edison HATED AC and wanted DC in everyone's house with a small generator in a barn out back.


That's actually the exact reason AC became the standard! You see Edison did many demonstrations showing how dangerous AC current was in comparison to DC. He maintained that it would be the perfect thing for executions for example. Well the short version is that the government tried it out, and agreed it was good for the electric chair. Now the government needs to buy AC generators, and the rest is history. That's just from memory but you can find the info if you're interested.


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## markba633csi

Yes John H. however- the cap is in series with which winding? The start winding.  Same thing in the 220 volt configuration except the run windings are in series not parallel,  and the start leg is in parallel with one of the run legs.  The junction of the two run windings should be 0, by voltage divider.  And that's the reason you can use the same 110 volt start winding for 220.  You're still getting a phase shift between the start leg and the parallel run leg.  Right?  
Mark S.


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## juiceclone

OK just for a little more mud in the water, below are the secondaries of both delta and wye transformers.
when ,in the US, you use 220 or 110 you are using two connection points, NOT two different phases as you can visualize from the pix.  
Other parts of the world use delta with it's "floating" /no ground.  Have run into both types working on cruise ship equipment.  A meter reading from one leg of a delta sys to "ground" produces some ...interesting... results.


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## hanermo2

Earlier, it was mentioned, incorrectly imo, that the EU and global power uses only one line for power.
Most of the world is 220V (240V) single phase, residential, at 50 Hz.

The std residential single phase service uses 2 lines for power.
And a green/yellow safety ground, not used at all.

Unlike in the US, plugs are not keyed.
You can use either line, since its AC, and both lines carry an identical load.

Typically, up to about 4-6 kW is single phase, and around 4-6 kW you start to get 3-phase used, for example for saunas (or larger jacuzzi).
Most new EU residential installs have 3-phase at the fuse box, as standard.
And typical power levels are 10-15 kW, up to 20 kW, new, in the EU.

I have about a 20 kW install, older, in Spain, and this is quite unusual.
Technically, the service is iirc about 14-16 kW, 380 V 3-phase, with all appliances done at 220V single phase.

But I have 380V 3-phase wired in several places, just not in use at the moment.
So I could connect say an electric car plug, and charge at 14-16 kW, if I wanted to.

Any electrician can connect the plug, and it costs about 100$ (legal install, no paperwork necessary).
Since I already have the service, and internal wiring, the current installs like mine are grandfathered in.


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## Downunder Bob

I think terminologies are  the problem here. different countries and possibly even states use different names for the same things, then to add to the confusion they use the same names to describe different things.

Single phase is single phase irrespective of the voltage in single phase the sine wave goes from + volts to - volts of the same value, be it 110 or 220 0r even 240v. crossing the zero line midway, all phases derived from 3 phase will be 120 deg apart, a transformer cannot change this, I have never heard of phases being 90 or 180 deg apart unless it came from a two phase generator or rotary converter, but I have never seen or heard of one, I'm sure it's possible. 

A two phase service to a consumer will simply be two of the three phases split from a three phase supply. each phase will consist of a single active wire and a common neutral wire. two phase is not normally used to run motors but is often used to supply electric cookers and other heating equipment. Two or three phase will be supplied to a consumer where a single phase cannot supply sufficient current for the total load.


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## ddickey

I'm pretty sure there is no two phase provided to consumers.


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## Downunder Bob

ddickey said:


> I'm pretty sure there is no two phase provided to consumers.


You might like to think that, but I know people who are on a two phase supply.


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## tq60

If not so good memory is somewhat correct...There was some 2 phase power systems back in the rust belt area from the early days when ac and dc power systems were both in use.

The phases were 90 degrees apart maybe and still in use a few years back when we read about it.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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## ARKnack

Just to add to the confusion.
Also I had heard the Detroit still had some 2 phase power around 20 years ago. They may still have some


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## Downunder Bob

The American system has always confused me. Here in downunder we have a system similar to Europe. distribution from the power station is via 3 wire 3 ph at a variety of very high voltages, this is broken down into local service areas at substation and sent out as 3ph 4wire ie. 3 actives and a neutral at usually around 3,300v  This is then further reduced with local area transformers to 415/440v 3 ph still in 4 wire configuration. This is then supplied on the power poles throughout the local area.

 Instead of having the small transformers, or pole pigs, as you guys call them we have much larger transformers servicing a larger area, this is all 4 wire 3ph 415/440v. the individual supply to local consumer can be single ph 2 ph or 3 ph depending on consumption requirements. 

Most homes that have gas available (that is domestic natural gas, not petrol) used for cooking , hot water and heating, will only have single ph, those that require more power if they are all electric, cooking hot water and heating etc will often have 2 ph, ( this is not split phase as in US, but two of the three phases at 120 deg. apart, from the pole.

 The two phases will be distributed around the house as single ph only, possibly with the exception of the cooker which if large may use the two phases separately to supply different elements. This can result in an interesting situation where one of the two phases fails, half the lights and appliances in the house will still work but the others will not. This can also happen in  a 3 ph installation.

Electricity is quite expensive here, on average about double the average price in the US so it is rarely used for heating other that cooking.

This two phase is never used for motors. In cases where large air conditioning or swimming pools or home workshop 3 ph can be supplied direct from the pole. 

My house is supplied with 3ph but only has one 3 ph outlet which is in the garage. I was going to get a 3ph welder, but never did.  All other appliances use single ph 240v. So it sits there unused. I could fit a 3ph motor to my lathe, but why bother the single ph motor gives me all the power I need. Maybe one day if the motor ever needs replacing.


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## olduhfguy

In AU most residences have 3 phase 240v available outside their houses, in US most residences have only single phase available and it appears as 240 volts which is tapped and grounded in the center (split phase), giving 120 volts for small appliances and 240 volt for larger ones. AU uses small numbers of large transformers serving many houses, US uses large numbers of small transformers serving at most 3-4 houses.


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## Superburban

Ok, so how does all this work for the electric meter? If the hot legs are not evenly loaded, can the meter tell and account for the difference?


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## olduhfguy

There is a technical description on Wikipedia: 

https://en.wikipedia.org/wiki/Electricity_meter

I have wondered about this myself - The answer must lie in the number and mechanical orientation of the coils so unbalanced loads spin the disc at a speed half the difference between the 2 loads. The 240 volt component (balanced load) needs adds full rotation speed and the unbalance adds half the speed. Then again, an electronic meter would just have one coil for each 'leg' and perform the necessary calculation in software.


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## ddickey

They only care about kilowatts


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## markba633csi

I only care about pizza- 
and beer


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## BROCKWOOD

I've worked for 2 power companies, both in distribution & transmission for 26 years.  If read start to finish, you guys have it all figured out. I'll attempt an additional explanation of the USA 120/240V residential power transformer.  Current does have a flow direction & that direction is back to ground.  Since the center tap of the 120/240V transformer is connected to ground, the flow or direction of the phase angle for each leg is in opposite directions or 180 degrees out from each other. But what about the 240V use of the same transformer?  It doesn't use the ground or neutral. True the 240V circuit completes itself.  The transformer on the pole has the neutral connection on the primary side.  Let any part of that 240V system have chance & it's going to ground to get back to the source.

Quick story similar to the O'scope your power feed joke.  A field tech thought that since his Fluke 87 says O.L. for overload above 600V he could measure the primary of a station power pot, 7200 phase to ground. Not sure how he lived to tell the tale.  The meter leads melted immediately.  The meter died permanently. The field tech suffered permanent hearing damage.


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## Winegrower

Not sure how I stumbled onto this ancient thread.   Certainly a lot of interesting explanations here.   

Let me just say this:  do you ever wonder why three phases and 120 degrees comes about?   It is because, surprisingly enough, if you sum the phases, it adds to a constant number, anywhere during a full cycle.  That is why 3 phase is said to be “smoother” than single phase, which drops to zero so many times per second.  Does that matter for a lathe or mill?   That I do not have any direct comparison for, just know that all the motors I have seem pretty smooth.


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## Catshooter

My first (and only) experience with "2 phase" was in Seattle at the Ball Glass plant.  They (the site electricians & electrical engineers) call it square phase.  

The glass furnaces are initially fired with natural gas and then switched to electric.  Incoming is 26.4 KV transformed down to 135/265.  The furnaces are very square and the opposing poles are placed in the corners via three for each side of the corner three inch stainless round bars.  Each bar is clamped to six 750MCM conductors and they get fed in as they are consumed.

The power is run around the outside of the furnace in a paralleled open bus, two 1x12 alum bars.

None of this is insulated.

Consumption is a bit over 10,000 amps.  Runs 24/7 for hopefully ten years or so.  Impressive.  

The EMF floating around these things is impressive too.  One day a man came in and set down a just fixed porta band.  We were working under the furnace and there is a lot of steel superstructure.  When he put the saw down, the ground prong happened to contact a piece of steel.  The cord was wrapped in a small circle, with three turns, held with twisty ties.  Didn't take long and it was smoking.  After we noticed it, we Amprobe clamped it - it was drawing +40 amps.


Cat


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## rwm

This company converts 2 phase power to 3 phase:





__





						Two Phase Electrical Service - What To Do - by Able Group Inc.
					

Two Phase PECO Utility Service, costs and info for the Philadelphia PA



					www.phillyfacility.com
				




Robert (formerly from Philly)


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## RJSakowski

If some of the content has already been covered, please forgive.  That is an awful lot of reading for a Sunday, even if it is an electrifying subject.

Out in the boonies in Wisconsin, our electric service is single phase.  Two wires can only supply a single phase.  The nearest three phase lines are about five miles away. They are only routed where there is enough demand to justify running the additional wire.

Three phase generation from a a single phase can only be done in one of three ways: A static phase convereter using reactance (capacitance and/or inductance) to electrically shift the phase, a rotary phase converter where secondary windings on a motor are physically positioned 120º and 240º from the primary winding, and using a VFD to create three new phases 120º apart.  I suppose using single phase to drive a motor driving a three phase generator would be a fourth.

An excellent reason for 120/240 is efficiency.  On the standard 120-0-120 feed, the most tcurrent the neutral will ever carry is the larger curren of the two legs as the neutral current is the difference between the currents in each leg because they are 180º out of phase.  It is the reason that we can use a 12-3 cable instead of a 12-12-8,   If two equivalent lines that were in phase, an additional wire would be required.  

The same is true for three phase.  The current through a wire will be the vector sum of the currents in the two connected circuits.  Because of the 120º phase shift, it will be less than the current in either circuit.  

Add to that, that three phase is better for converting to d.c.  With full wave rectification, there are six peaks per cycle instead of two.  The peaks are 2.7 msec. apart rather than 8.3msec. for single phase full wave rectification which means better voltage regulation and lower cost filtering.  Modern automotive alternators are three phase generators using full wave rectification.


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## rwm

"Modern automotive alternators are three phase generators using full wave rectification. "

I had no idea!
R


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## john.k

And then there is SWER with single phase motors up to 20 hp/400V.


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## RJSakowski

john.k said:


> And then there is SWER with single phase motors up to 20 hp/400V.



The farm that I eventually bought had a SWER wiring scheme of sorts..  Rather than run a neutral back to the meter, they relied on the black iron water pipe to provide the neutral.  At a later date, they replaced the iron with polyethylene.  It made for some interesting moments depending on how balanced the lines were.  I had measured as much as 40 volts from the neutral to earth at times.


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## CluelessNewB

rwm said:


> "Modern automotive alternators are three phase generators using full wave rectification. "
> 
> I had no idea!
> R



And some high output alternators for marine, RV and trucks are 6 phase!


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