# Single phase 208(2 wire) vs. Three phase 208 (3 wire) circuits



## 3D Electric (Mar 24, 2013)

ARCSNSPARKS49 said:


> Hey everyone, i had a question hope you guys can help. Ive come across 3 phase 208 circuits(3 hots) and single phase (2 hots) circuits. And was wondering what the differences were. I do know that in both line to line = 208v but dont know the differnces between both


Please see below


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## 3D Electric (Mar 24, 2013)

It sounds like you have a three phase 208 system and someone only needed a two pole single phase circuit. It's a common installation.


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## 3D Electric (Mar 24, 2013)

Stupid phone wouldn't let me reply the right way lol


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## FrunkSlammer (Aug 31, 2013)

ARCSNSPARKS49 said:


> Hey everyone, i had a question hope you guys can help. Ive come across 3 phase 208 circuits(3 hots) and single phase (2 hots) circuits. And was wondering what the differences were. I do know that in both line to line = 208v but dont know the differnces between both


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## Ultrafault (Dec 16, 2012)

FrunkSlammer said:


>


This is why no one asks questions around here. Cut the guy some slack. We all have to learn somehow.


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## 3D Electric (Mar 24, 2013)

Ultrafault said:


> This is why no one asks questions around here. Cut the guy some slack. We all have to learn somehow.


I know, that's why I told him. What's funny is my apprentice asked the same question a couple weeks ago. Lol


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## ponyboy (Nov 18, 2012)

We had a 5 page thread on this not too long ago and I'm pretty sure the guy still didn't get it. It's an elusive concept


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## 3D Electric (Mar 24, 2013)

ponyboy said:


> We had a 5 page thread on this not too long ago and I'm pretty sure the guy still didn't get it. It's an elusive concept


Did the thread get closed? If not I suggest the op read that thread. There is probably a lot of good information in it. I haven't seen it but between everyone on here there is a lot of knowledge.


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## Chrisibew440 (Sep 13, 2013)

You have three phases of electricity all at seperate times being generated. Single phase two wire is just two of those phases. You can use single or three phase loads out of a three phase system. Shall we get into why it's called single phase with two conductors?


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## Dylanewilliams (May 17, 2013)

Out of curiousity, why is there no difference between single phase 240 where the phases are 180 out and 208 where the phases of a 2 pole circuit are 120 and 240 out of phase? They both operate the same equipment generally without problem


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## 3D Electric (Mar 24, 2013)

Dylanewilliams said:


> Out of curiousity, why is there no difference between single phase 240 where the phases are 180 out and 208 where the phases of a 2 pole circuit are 120 and 240 out of phase? They both operate the same equipment generally without problem


There is a difference. The thing is an appliance (let's say a range) has a tolerance for varying voltages. Not every single phase 240 volt service will be exactly 240 volts. Hell my house is actually 228 volts. The further away from the rated voltage of the appliance you are the less efficient it will run. If you go outside its tolerance it may not run at all. We have a 120/208 the phase system at our shop and the range be have in the kitchen there is a 240 volt rated appliance. It cooks properly and that's all I can hope for.


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## FrunkSlammer (Aug 31, 2013)

Close this thread before the public realizes we're all a bunch of hacks who have no idea how lektricity works!

WE CHARGE HOW MUCH PER HOUR?


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## Chrisibew440 (Sep 13, 2013)

Well if equipment is rated for a certain voltage, the best thing to do is give it that but like you know this isn't always possible. The equipment will work either way because its still seeing a difference in potential. And there is stuff out their that has 10%, 15% etc tolerance level where the required voltage needs to be met within the tolerance percentages.


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## Dylanewilliams (May 17, 2013)

Im not talking about difference in voltage, im talking about difference in the offset of the phases in the voltage


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## Dylanewilliams (May 17, 2013)

3D Electric said:


> There is a difference. The thing is an appliance (let's say a range) has a tolerance for varying voltages. Not every single phase 240 volt service will be exactly 240 volts. Hell my house is actually 228 volts. The further away from the rated voltage of the appliance you are the less efficient it will run. If you go outside its tolerance it may not run at all. We have a 120/208 the phase system at our shop and the range be have in the kitchen there is a 240 volt rated appliance. It cooks properly and that's all I can hope for.


To clarify in a different way, 3 phase is 2/3 pi out of phase where as single phase is pi out of phase. Why doesnt that make a difference in how utilization equipment operates?


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## 3D Electric (Mar 24, 2013)

Dylanewilliams said:


> To clarify in a different way, 3 phase is 2/3 pi out of phase where as single phase is pi out of phase. Why doesnt that make a difference in how utilization equipment operates?


It's a matter of the transformer used. Comparing a single phase transformer and a three phase transformer is like comparing a Wye transformer to a delta. They are completely different systems and operate differently. I'm trying to think of the best way to easily explain it lol.


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## Ultrafault (Dec 16, 2012)

Dylanewilliams said:


> Out of curiousity, why is there no difference between single phase 240 where the phases are 180 out and 208 where the phases of a 2 pole circuit are 120 and 240 out of phase? They both operate the same equipment generally without problem


I think you must be referring to 120/240 split phase. That is one single phase both lines are 180 degrees from the center tap (neutral). 
It is best for me to imagine wires are points each point has a diffrent potential to the two other points at any given time. I then imagine the phase as a line.

If you draw a trinagle with 3 points and 3 lines you can visualize my reprentation of 3 phase power.To have 3 phases we must have 3 points. If I take two points or two wires I only have one phase becuase I can only draw one line. Likewise a 2 phase system requires 4 points or wires.
A voltage (a phase) does not exist on a single point it can only be between 2 points. You can test this by putting an apprentice on a rubber mat and putting a wire in his mouth (DON'T DO THIS).

There can be no phase angle difference from one single phase becuase you cannot compare something to nothing.


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## Dylanewilliams (May 17, 2013)

I understand how transformers work, thats not my question. I am curious why phase angle doesnt affect utilization equipment


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## Ultrafault (Dec 16, 2012)

Dylanewilliams said:


> I understand how transformers work, thats not my question. I am curious why phase angle doesnt affect utilization equipment


What phase angles are you referring to?


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## Dylanewilliams (May 17, 2013)

Ultrafault said:


> What phase angles are you referring to?


Phase angle between the legs of the circuit. From physics i remember phase angles create reactance, but ive never had a problem installing a 2 pole device on a 3 phase switchboard


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## Ultrafault (Dec 16, 2012)

Dylanewilliams said:


> Phase angle between the legs of the circuit. From physics i remember phase angles create reactance, but ive never had a problem installing a 2 pole device on a 3 phase switchboard


Phase angle in this sense means the difference in time between the 3 separate phases of a 3 phase system. Two wires gives you one single phase. There is no phase angle difference between one phase and its self. Poles are not phases wires are not phases. A phase is the ac voltage and current between two wires or poles. It is hard to explain without visual aids and explaining is not my strong suit. 
I was not talking about transformers earlier.


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## Dylanewilliams (May 17, 2013)

Ultrafault said:


> Phase angle in this sense means the difference in time between the 3 separate phases of a 3 phase system. Two wires gives you one single phase. There is no phase angle difference between one phase and its self. Poles are not phases wires are not phases. A phase is the ac voltage and current between two wires or poles. It is hard to explain without visual aids and explaining is not my strong suit.
> I was not talking about transformers earlier.


What i understand is the following: AC current is delivered as a sine wave. Grounded conductor to one phase leg looks like a sine wave. Phase next to phase on an oscilloscope looks two sine waves. In a single phase transformer they are 180 degrees out of sync. In a 3 phase transformer they are 120 or 240 degrees out of sync. Im not following the "draw a straight line" explanation?


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## stuiec (Sep 25, 2010)

Dylanewilliams said:


> What i understand is the following: AC current is delivered as a sine wave. Grounded conductor to one phase leg looks like a sine wave. Phase next to phase on an oscilloscope looks two sine waves. In a single phase transformer they are 180 degrees out of sync. In a 3 phase transformer they are 120 or 240 degrees out of sync. Im not following the "draw a straight line" explanation?


What do you really want to know?


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## Ultrafault (Dec 16, 2012)

Dylanewilliams said:


> What i understand is the following: AC current is delivered as a sine wave. Grounded conductor to one phase leg looks like a sine wave. Phase next to phase on an oscilloscope looks two sine waves. In a single phase transformer they are 180 degrees out of sync. In a 3 phase transformer they are 120 or 240 degrees out of sync. Im not following the "draw a straight line" explanation?


Ok I need to understand where you are at.
How many phases do you think two wires of a 3 phase system constitutes?

To answer your question about a split phase transformer it is not two phases 180 degrees apart it is one phase. You are simply observing it from diffrent reference points.


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## sparky970 (Mar 19, 2008)

Dylanewilliams said:


> I understand how transformers work, thats not my question. I am curious why phase angle doesnt affect utilization equipment


Do you have phase angle requirement on the nameplate? I have only dealt with phase angle when synchronizing 2 power sources. So in a single phase system, you have 2 hots, A and B, they provide 208v in your case. In a 3 phase system, you have 3 hots, A-B=208v, B-C=208V, A-C=208V


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## hardworkingstiff (Jan 22, 2007)

*My attempt*

Here is my attempt to explain what I think the OP is asking.










In the drawing, if you consider the 4 points (A,B,C,N) and compare the A,B,C to N, you can easily see that there are 3 phases 120 or 240 degrees out from each other.

If you hook up utilization equipment to just A and B, then the equipment will only see the voltage between A and B. If you were to connect A and B to a scope (no neutral or ground reference) you would get just one sine wave and you would not know it was derived from a 3-phase system. The equipment will only see the one sine wave and it is single-phase.

The "lines" talked about earlier are the lines drawn between any 2 phases (A to B, B to C, or C to A). Any one of those 3 lines are single-phase, it's only when you introduce another leg that you can see a phase "offset".

IMO, I think is is terrible that we call 2 legs and a neutral from a wye distribution to be "single-phase" since the neutral is not on the line drawn between the two phases.


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## 8V71 (Dec 23, 2011)

I know what he is asking but I can't find the words to describe it without showing an image. My post might not even be right so feel free to correct me if I'm off base here.

Below is a real time image of a split phase service like to a residence. Just shift the green or red over a bit for hooking up to 2 legs of a 3 phase service. What is important to the single phase equipment is the potential between the 2 waveforms and not necessarily when they are occurring in relation to each other.


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## Meadow (Jan 14, 2011)

Phase angle just gives you 208 instead of 240.

Think of it like this, instead of voltage being double its just the square root of 3.


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## Pharon (Jan 20, 2014)

ARCSNSPARKS49 said:


> Hey everyone, i had a question hope you guys can help. Ive come across 3 phase 208 circuits(3 hots) and single phase (2 hots) circuits. And was wondering what the differences were. I do know that in both line to line = 208v but dont know the differnces between both


The main difference is you get more power from 3-phase. Let's say you're drawing 10 amps per phase:

1-phase 208 power: 10A * 208V = 2080 VA
3-phase 208 power: 10A * 208V * sqrt(3) = 3603 VA


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## TitoM0907 (Oct 29, 2020)

New to this page. 
Quick Question.? 
I have a 120/208 3 phase 4 wire service
So I need to add a 120/208 1 phase sub panel.
I have 120 v from A phase to N
208v from B phase to N 
120v from C phase to N 
240v from A Phase to B phase 
240v from B phase to C phase 
240v from A phase to C phase 
My question is, will be able to use the 208 leg on sub panel??(It could be either A phase or B phase, depending on which one I use.)(Can’t go with A phase to C phase since that would be 120/240 1 phase.) sorry guys!


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## macmikeman (Jan 23, 2007)

Tito , what is your occupation? This kind of question leads me to believe you are either an apprentice or else a non electrician. Can you fill in your profile page , this is kinda Elec 101 stuff real electricians all know so you are suspect at this point.


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## gpop (May 14, 2018)

TitoM0907 said:


> I have a 120/208 3 phase 4 wire service


120/208 would be a Y. 
Your reading are for a open delta.


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## TitoM0907 (Oct 29, 2020)

Ok guys so I do residential and haven’t really dealt with 3 phase. So I understand how it works but what is throwing me off is that the blueprints call for a 120/208v single phase-3 w sub-panel fed from a 120/208-3 phase-4 wire. (This is for a smoothie king remodel) (Service is already there)


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## splatz (May 23, 2015)

TitoM0907 said:


> Ok guys so I do residential and haven’t really dealt with 3 phase. So I understand how it works but what is throwing me off is that the blueprints call for a 120/208v single phase-3 w sub-panel fed from a 120/208-3 phase-4 wire. (This is for a smoothie king remodel) (Service is already there)


From the thread you started, the drawing expects 208/120 wye and you have 240/120 high leg delta. Tell your customer there's a discrepancy between what's drawn and what you found, have them take it to their engineer and the engineer will deal with it. Don't try to hack your way through it.


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## TitoM0907 (Oct 29, 2020)

Another question? Could it be a 3 phase 4 wire delta??


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## TitoM0907 (Oct 29, 2020)

TitoM0907 said:


> Another question? Could it be a 3 phase 4 wire delta??


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## splatz (May 23, 2015)

TitoM0907 said:


> Another question? Could it be a 3 phase 4 wire delta??


Why didn't I think of that?


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## TitoM0907 (Oct 29, 2020)

So my question still is can I use that wild leg to feed my sub-panel? Or should i use(Both 120 legs) C be phase & A phase.The blueprints call for 120//208v single phase 3 wire


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## TitoM0907 (Oct 29, 2020)

So my question still is can I use that wild leg to feed my sub-panel? Or should i use(Both 120 legs) C phase & A phase.The blueprints call for 120//208v single phase 3 wire sub-panel.


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## brian john (Mar 11, 2007)

TitoM0907 said:


> So my question still is can I use that wild leg to feed my sub-panel? Or should i use(Both 120 legs) C phase & A phase.The blueprints call for 120//208v single phase 3 wire sub-panel.


You need to get with your customer and explain what you have is not what is specified


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## micromind (Aug 11, 2007)

The prints likely call for 120/208 because the engineer is lazy and doesn't want to spend any time with the actual job. He is using the same specs he has used on jobs in the past.

The actual reality is it very likely won't matter if it's 120/208 3 phase or 120/208 single phase or if it's 120/240 single phase.

The only possible thing that could matter is if there is equipment designed for 208 only and not 240. Very rare but it does happen.


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