Balance Load for a 2 Phase 120/240 System

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Electricalhelp

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How do I balance the load for a 2 Phase 120/240V System?

For a 3 Phase System - I would balance the total load between A,B & C and then divide the VA by 240*√3 .

For a 1 Phase System - I would balance the total load between A & B and then divide the VA by 240.

So how many phases (A,B,C etc) will there by for 2 Phase and what would I divide the total load by.
 
synchro said:
Pick which version that you want:
3-wire with a neutral
5-wire with a neutral
4-wire no neutral


I just was you mentioned 120/240 so that would be 5-wire.
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I'm not sure if it's 5 Wire or 3 Wire.
But if it was 5 wire, do I need A,B,C,D & E Phases and then what do I divided the total by

If it was 3 wire, do I need A,B, & C Phases and then what do I divided the total by
 
A two-phase set-up is usually made of two independent single-phase supplies with a single interconnection, and calculated thusly.
 
Electricalhelp said:
How do I balance the load for a 2 Phase 120/240V System?

For a 3 Phase System - I would balance the total load between A,B & C and then divide the VA by 240*√3 .

For a 1 Phase System - I would balance the total load between A & B and then divide the VA by 240.

So how many phases (A,B,C etc) will there by for 2 Phase and what would I divide the total load by.
Click to expand...

What you know as a "1 phase system" behaves exactly as what it would do in a hypothetical "2-phase system". The difference is the semantics for whether the system is produced by forming two waveforms that are inverses of each other as a result of centertapping a transformer, or forming two separate waveforms at the source that are 180 degrees apart. The end result is the same, and it is just a matter of industry nomenclature that we don't call it a two phase system.

We don't call it 2-phase, because of the mechanics of how it is produced from a 3-phase grid. An individual phase from the 3-phase grid, supplies the primary side of the single phase transformer. Then, the voltage is stepped down to 240V, and centertapped to derive the neutral for the service. Because it comes from an original single phase pulled off the 3-phase grid, it is called single phase. I prefer the term "split phase" because it references the essential feature of centertapping to derive the neutral.
 
Tesla’s original patent is for a two phase system. They are 90 degrees apart. I’ve read that a Scott T transformer can convert this to three phase but don’t have a use for it.

240/120 is single phase aka “split phase”. You can have it as 3 wire (240 V plus ground), 4 wire (240/120 plus ground), or a 3 wire version which is one of the 240 V hot legs plus neutral and ground.

Only way I can see “5 wire” is if you use a second single phase transformer in broken delta high leg or a true three phase transformer also in delta high leg so we would have the split phase 240/120 but also a third phase wire where the original two plus the new third form a 3 phase system.

As to balancing on high leg delta you can’t. Three phase loads are inherently balanced but all single phase loads are not. The only way to achieve that is on 208/120 4 wire wye but you lose the 240 V supply. You can sort of fake it with 208 but the neutral is off angle.
 
Carultch said:
What you know as a "1 phase system" behaves exactly as what it would do in a hypothetical "2-phase system". The difference is the semantics for whether the system is produced by forming two waveforms that are inverses of each other as a result of centertapping a transformer, or forming two separate waveforms at the source that are 180 degrees apart. The end result is the same, and it is just a matter of industry nomenclature that we don't call it a two phase system.

We don't call it 2-phase, because of the mechanics of how it is produced from a 3-phase grid. An individual phase from the 3-phase grid, supplies the primary side of the single phase transformer. Then, the voltage is stepped down to 240V, and centertapped to derive the neutral for the service. Because it comes from an original single phase pulled off the 3-phase grid, it is called single phase. I prefer the term "split phase" because it references the essential feature of centertapping to derive the neutral.
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I believe the OP is talking about two 1ph waveforms that are 90 degrees apart. 4-wire would mean no interconnection, 5-wire would be two center-tapped sources with the neutrals tied together as a common neutral, and 3-wire would be an L connection.
 
paulengr said:
Only way I can see “5 wire” is if you use a second single phase transformer in broken delta high leg or a true three phase transformer also in delta high leg so we would have the split phase 240/120 but also a third phase wire where the original two plus the new third form a 3 phase system.
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See what I just posted about 5-wire.
 
I'm just confused on how to calculate the total Amperage of a system with a 2 Phase 120/240 System

Not sure how I create a Panel Schedule to calculate the total amperage of the system. Is there an example of a 2 Phase Panel Schedule I can take a look at how the balanced the load.

Do I still have all three Phases and divided the system by 240V to get the total amperage
 
The real question is Do you really have 2-phase? Unless you're in Center City Phila, parts of Hartford CT, or one or two other places, you probably don't.

Or are you working with a 240/120v 3-phase high-leg delta and staying with the center-tapped pair. If you could dig up a drawing/sketch of the actual connections, that would explain things.
 
zbang said:
The real question is Do you really have 2-phase? Unless you're in Center City Phila, parts of Hartford CT, or one or two other places, you probably don't.

Or are you working with a 240/120v 3-phase high-leg delta and staying with the center-tapped pair. If you could dig up a drawing/sketch of the actual connections, that would explain things.
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I am working on a project in Center City Philadelphia.

The PECO agent told me the only service they have is 2 Phase 120/240 System
 
Electricalhelp said:
I am working on a project in Center City Philadelphia.

The PECO agent told me the only service they have is 2 Phase 120/240 System
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They've got to have very special information if what you're saying is accurate, because true 2-ph is almost extinct.

Ask how many ungrounded (hot) wires they will be presenting, and whether there will be a neutral.
 
Electricalhelp said:
I'm just confused on how to calculate the total Amperage of a system with a 2 Phase 120/240 System

Not sure how I create a Panel Schedule to calculate the total amperage of the system. Is there an example of a 2 Phase Panel Schedule I can take a look at how the balanced the load.

Do I still have all three Phases and divided the system by 240V to get the total amperage
Click to expand...
If it's a 5-wire system, say that phases A, B, C and D are at 0°, 90°, 180°, and 270° respectively and the fifth wire is the neutral N. Are all your loads single phase 120V or 240V loads like in a common residence? If so then you would first calculate
the currents on A, C, and N from your loads on these phases just like you would on a common 120/240 split-phase system. Call those currents IA, IC, and INx. Then again calculate the currents on B, D, and N from your loads on these phases as in another 120/240 split-phase system. Call those currents IB, ID, and INy. The total neutral current IN = √( INx2 + INy2) because INx and INy are 90° apart, assuming unity (or at least the same) power factor for the loads.
You then have the current on all 5 wires: IA, IB, IC, ID, and IN.

In the unlikely event the you have actual 2-phase loads from motors, etc. you'd have to provide more details about them.
 
So if the system there giving me is 600 AMP 2 Phase 120/240 System.

So for example
A: 1000 VA
B: 1000 VA
C: 800 VA
D: 500 VA

The load for A/C/N would be 1800/240 = 7.5 A
The load for B/D/N would be 1500/240 = 6.25 A
So the total load of the Panel will be 13.75 A

What Panel manufacture make these Panels


I do not have loads 2-Phase loads from motors. Most equipment are 240/1Ph kitchen equipment
 
The PECO "blue book" says that it's 5-wire, and that's about the only sensible configuration. And it accounts for all of the 4-pole switches I've seen pictured.

Panel manufacturers? Good luck :D. I may be wrong but doubt that anyone has made a 2-phase panel in 50 years. Unless there's a good reason, I'd treat A/B and C/D as separate single-phase systems.

Also, I've heard that a lot of rewires in Center City go from the 2-phase service disconnect directly into a Scott-T transformer to make 3-phase and go from there.

(Interesting but not related- "The Company will extend a fourth wire neutral to supply 120/240 volt single-phase equipment in combination with this service. Service capacity per phase will not exceed 15 kVA.")
 
zbang said:
The PECO "blue book" says that it's 5-wire, and that's about the only sensible configuration. And it accounts for all of the 4-pole switches I've seen pictured.

Panel manufacturers? Good luck :D. I may be wrong but doubt that anyone has made a 2-phase panel in 50 years. Unless there's a good reason, I'd treat A/B and C/D as separate single-phase systems.

Also, I've heard that a lot of rewires in Center City go from the 2-phase service disconnect directly into a Scott-T transformer to make 3-phase and go from there.

(Interesting but not related- "The Company will extend a fourth wire neutral to supply 120/240 volt single-phase equipment in combination with this service. Service capacity per phase will not exceed 15 kVA.")
Click to expand...

A: 1000 VA
B: 1000 VA
C: 800 VA
D: 500 VA


The load for A/C/N would be 1800/240 = 7.5 A
The load for B/D/N would be 1500/240 = 6.25 A
So the total load of the Panel will be 13.75 A

So regardless which phase, A/B or C/D, I assume I'm calculating the total correctly above of 13.75 A for a 2Phase system
 
For two phase calcs you use square rt of 2, 1.414
Just like you use square rt of 3 for three phase.

For the last two phase service I worked on before I moved (~1999) there was a 4 pole service disconnect to a wireway, then taps for 4 pole disconnects to two phase motors, then a single phase panel off each phase.

Siemens used to offer a two phase P3 panel, its in the 2007 speedfax. You can still special order them.
Since you don't have motors you could just set two single phase panels and treat it like two single phase services.
If you still did the 4 pole disconnect, you could have options for a Scott-T if they ever needed 208Y motors.
Dont forget the neutral upsizing.
LarryFine said:
They've got to have very special information if what you're saying is accurate, because true 2-ph is almost extinct.

Ask how many ungrounded (hot) wires they will be presenting, and whether there will be a neutral.
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Larry I believe lots of the down town Philadelphia grid is still two phase. :)
If your ever touring the liberty bell / independence hall area scott connected transformers can be seen on poles to get customers three phase.

Photo of a two phase disconnect:
siemens2phase.jpg
 

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