# 240V/120V, 3 Phase, 4 Wire System @ 60Hz



## VikingJoe

Hello Everyone,

Name is Joe and I am currently working on a project to bring 240/120, 3 Phase, using 4 wires (center-tapped phase for neutral) into our builds. 

First thing to say, is WOW, not much out there when talking about the basics of the 3 phase power, and how to balance the system. 

To be clear, the wikipedia page for this setup is shown here: 
http://en.wikipedia.org/wiki/High-leg_delta

So, after my reading I am getting a feel for how this all works. Funny thing is the more you read, the more confused you can get. Some information I read is quite basic, then some information I read gets downright crazy. I love math as much as the next guy, but there is a point.

The biggest issue/concept that I am trying to take on is that in this system I am going to have loads that are: 240 3-phase (motors & AC compressors), 240 split(single) phase (appliances, heating elements, and 120 single phase. 

Thus why I am using the setup. I am embarrassed to say that I just cannot wrap my head around the proper way to balance out my electrical panel. I have figured out that it is not as simple as adding all the amps for each of the three phases (legs).

To be clear, if B is my "high" leg, and I were to put a 120V lamp of 1A off leg A, and neutral, a 120V lamp of 1A off leg C and neutral, a 240V heating element of 15A off leg B & C, a 240V stove of 8A off leg B & A and then finally a 7A motor 240V 3-Phase I know that the total of each leg is NOT.

Leg A: 1A + 7A +8A = 16A total

Leg B: 7A + 15A + 8A = 30A total

Leg C: 1A +7A + 15A = 23A total 

Correct ?

More embarrassing still, I will give you what I think the answer would be


Leg A: 1A + 7A +8A = 16A total

Leg B: 7A + ((15+8) * srt3)) 46.8A <--- I know that is wrong. 

Leg C: 1A +7A + 15A = 23A total


Well that is the issue. My goal is to have a balanced system on the panel, and then after adding all the loads to calculate my kW. Simple enough right ? 

Yet, after putting a good 1/2 day into it, so far I am a little lost. If I come up with any revelations then I will follow up this post.

Thanks to all. 
:thumbsup:


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## erics37

If you're running a bunch of 120 volt loads off a 3-phase delta service you don't want to do more than like 5 or 10% of the VA of the supplying transformer with A-neutral and C-neutral loads. Remember that winding is picking up a third of all the 3-phase loads as well as a bunch of your single-phase loads.

Balancing a high leg service is a bitch unless everything is 3-phase.

Have you considered getting a 208/120 Wye service instead? Most 3-phase equipment these days will take 208 just fine, and it's much easier to balance overall.


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## VikingJoe

erics37 said:


> If you're running a bunch of 120 volt loads off a 3-phase delta service you don't want to do more than like 5 or 10% of the VA of the supplying transformer with A-neutral and C-neutral loads. Remember that winding is picking up a third of all the 3-phase loads as well as a bunch of your single-phase loads.
> 
> Balancing a high leg service is a bitch unless everything is 3-phase.
> 
> Have you considered getting a 208/120 Wye service instead? Most 3-phase equipment these days will take 208 just fine, and it's much easier to balance overall.


1st off, thank you for taking the time to write back. 

If you didn't realize by now, this is a new world to me. 

Unless I am mistaken the reason I don't use the standard 208/120 is because I need 240 split-phase as well.

I have normal single phase loads - lights, etc., etc.

I have normal split phase loads - water heater, oven, dryer

and I have 3 phase loads - motors, Air Conditioning, water makers.

Again, I may be greatly mistaken but I believe I need to use a 120/240 in order to have access to all those types of power from one transformer. 

What more, for my application I a severely restricted in the amount of space to set this up in.

My hope is I have enough double pole, 240V split phase loads to try and balance out the high leg. 

I don't know yet, cause I have not figured out how to make an accurate load calculation (load grouping in the panel).

Not only that I am pretty sure from what I have been studying over the last few days that once I figure out what the total amperage on each leg is, I still have some more calculations to make in order to convert everything to Watts.

As I said...this is new territory for me. 

I have plenty of information on how to solve these problems in a text book, but what I am missing, and am continuing to work on is how to apply it to a real panel. 

Again, I maybe completely wrong on all this. Not about to tell guys who have worked with these types of things there whole life anything about it. Just here to learn.


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## VikingJoe

Note: I should also note I am at the mercy of very touchy Air Conditioning compressors, which I continue to read are finicky about getting 230 V.

Thus the Delta with the center tap.


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## erics37

VikingJoe said:


> 1st off, thank you for taking the time to write back.
> 
> If you didn't realize by now, this is a new world to me.
> 
> Unless I am mistaken the reason I don't use the standard 208/120 is because I need 240 split-phase as well.
> 
> I have normal single phase loads - lights, etc., etc.
> 
> I have normal split phase loads - water heater, oven, dryer
> 
> and I have 3 phase loads - motors, Air Conditioning, water makers.
> 
> Again, I may be greatly mistaken but I believe I need to use a 120/240 in order to have access to all those types of power from one transformer.
> 
> What more, for my application I a severely restricted in the amount of space to set this up in.
> 
> My hope is I have enough double pole, 240V split phase loads to try and balance out the high leg.
> 
> I don't know yet, cause I have not figured out how to make an accurate load calculation (load grouping in the panel).
> 
> Not only that I am pretty sure from what I have been studying over the last few days that once I figure out what the total amperage on each leg is, I still have some more calculations to make in order to convert everything to Watts.
> 
> As I said...this is new territory for me.
> 
> I have plenty of information on how to solve these problems in a text book, but what I am missing, and am continuing to work on is how to apply it to a real panel.
> 
> Again, I maybe completely wrong on all this. Not about to tell guys who have worked with these types of things there whole life anything about it. Just here to learn.





VikingJoe said:


> Note: I should also note I am at the mercy of very touchy Air Conditioning compressors, which I continue to read are finicky about getting 230 V.
> 
> Thus the Delta with the center tap.


Is this a residential application? 208 will work fine for just about all of that stuff. A/C compressors aren't finicky, they are just motors and in most applications are rated for 208-230, or even a dual winding setup enabling them to be used on 480V systems. At worst, you'll have to read the instructions and see if they need to have a jumper moved or something in the control panel. The compressor nameplate will yield the ultimate answer.

All of the other loads - dryers, ovens, water heaters, etc - will run fine on 208, they will just got slightly less hot. This is a very common application for apartments, condominiums, etc. If you stick with a high leg service you'll run the risk of overloading the A-C winding with all the 120V crap.

As far as calculations, that is almost a trade unto itself. Best bet would be to take a calculations class or have an EE do it for a fee.


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## erics37

Anyway our power company won't even supply a high-leg service for new construction anymore (unless there's some special permission granted but that doesn't happen). It has its place but a Wye system is generally more advantageous these days.


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## VikingJoe

erics37 said:


> Anyway our power company won't even supply a high-leg service for new construction anymore (unless there's some special permission granted but that doesn't happen). It has its place but a Wye system is generally more advantageous these days.


 
Ok.

I guess it is back to the drawing board then....which is all good.

I am going to attack the problem again from a 208-230 stand point, and see if I can get some of our manufacturers to work with us.

Again, thank you very much for your help.

If I work out the load calculations I will reply back to this thread for the sake of good information.


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## hardworkingstiff

erics37 said:


> All of the other loads - dryers, ovens, water heaters, etc - will run fine on 208, they will just got slightly less hot.


Slightly? If you do the math, the "slightly less" is 25% less. I think that's a bit more than "slightly".


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## hardworkingstiff

Last year I remodeled a building that had a 208Y/120 (1200-amp) service. They also had a bunch of refrigerated loads that needed 240V, so what they did is installed some buck-boost transformers to step up the voltage to a 400-amp panel to feed those loads.


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## VikingJoe

hardworkingstiff said:


> Last year I remodeled a building that had a 208Y/120 (1200-amp) service. They also had a bunch of refrigerated loads that needed 240V, so what they did is installed some buck-boost transformers to step up the voltage to a 400-amp panel to feed those loads.


Thank you, good to know.


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## wendon

Another thing you're going to run into if you connect "split phase" loads such as dryers and ranges to the A and B phase is the fact that you'll let out the smoke as they need 120/250 volt. Unless you're marginal on your service sizing I'd install a separate single phase panel connected to A and C phase.


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## RePhase277

Edit... beat to it.


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## hardworkingstiff

VikingJoe said:


> Thank you, good to know.


Just remember if you do something with buck/boost transformers that the line to neutral voltage in that panel will be 139V, so you would not want to feed any 120V loads out of it (I wouldn't even bring a neutral to it).


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## VikingJoe

Thanks again gentlemen for all your help.

Things are now progressing nicely. 

I can now balance out the system, understand how each leg effects the other two, and why sizing your neutral in these systems is VERY important. 

I hope to find the time to write up a follow up to this message.


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## Jerome208

Around here almost all small services are 2-transformer open delta with the lighting transformer way bigger than the power transformer, and pretty much all single phase loads are connected to the lighting transformer only. Often times the lighting transformer will be tapped off on the pole to feed another house or something that is single phase only. If it is done with a three transformer bank, then the two power transformers are still much smaller. 

In other words, with this type of setup, load balancing is not really even necessary. Just hook single phase loads to the A and C phases and leave the high (B) phase for three phase loads only. 

Of course, there is nothing wrong with hooking up 240 volt single phase loads across the other sides of the delta either, although with open delta I am not sure if you want to hook up across the open side, or if there is an easy way to tell inside the panel which is the open side of the delta and which is the "real" side.


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## BBQ

hardworkingstiff said:


> Slightly? If you do the math, the "slightly less" is 25% less. I think that's a bit more than "slightly".


Here we go again:laughing:

Again I point out this is normal it is done all the time 

And for the most part changes nothing, heating items like water heaters, ovens, space heat that are thermostatically controlled will get just as hot it will just add time to it.

Just like Eric's power companies ours will not provide a new high leg service. So in about eight bazillion buildings 208 is what you get.


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## hardworkingstiff

BBQ said:


> Here we go again:laughing:
> 
> Again I point out this is normal it is done all the time
> 
> And for the most part changes nothing, heating items like water heaters, ovens, space heat that are thermostatically controlled will get just as hot it will just add time to it.
> 
> Just like Eric's power companies ours will not provide a new high leg service. So in about eight bazillion buildings 208 is what you get.


You can laugh and joke all you want BBQ, but 240-volt rated equipment will work with 25% less power on 208-volts. I've never said it would not work, and I will never not complain about it. :laughing:


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## Deep Cover

I wish the OP would have included some more information like what type of application this is.

My general thinking is if this is a commercial/industrial, I'd look at bringing in 480V, then setting the appropriate transformers.


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