Phase unbalancing

shortcircuit1

Senior Member
Hello,

I am learning design slowly..While i am learning i run into some questions which maybe simple for some of you guys..I need that experience to help me learn better :).
So while you do the residential calculations per code and come up with the feeder sizes for individual and multifamily units.Now once you size the service you make the decision on meter banks.How many i need and how many meter stacks per section and width and so on...But what i have heard is i have to make sure that the load is balanced on all three phases..While i do know what the balancing is in general..But how do i make sure that the load is balanced in each section of the meter bank whether to use 3 stacks or 4 stacks per section?

As an example lets say you have 65 units and each individual unit load comes out to be 112A. How do you decide on how many meter banks once you size the service?And how to do the proper balancing?

Thanks,
shortcircuit.
 

Smart $

Esteemed Member
Your units get powered 120/208 1Ø 3W (an assumption on my part but you did mention three phase). That's two hots and a neutral. So you alternate them AB, BC, and CA. Where each unit has the same load, just alternating them balances the load... in sets of three. When you have one or two odd ones left, you cannot help but have an unbalanced system. Just have to make sure the equipment and conductors are properly rated.
 

shortcircuit1

Senior Member
Your units get powered 120/208 1Ø 3W (an assumption on my part but you did mention three phase). That's two hots and a neutral. So you alternate them AB, BC, and CA. Where each unit has the same load, just alternating them balances the load... in sets of three. When you have one or two odd ones left, you cannot help but have an unbalanced system. Just have to make sure the equipment and conductors are properly rated.
I can understand the balancing concept of just alternating between 2 phases. But lets say you have a meter bank with 12 meters with 4 on each section.Now how do you balance two phases on each meter? A simpe technique is just have AB-Meter 1 ,BC-Meter 2,CA- Meter 3 but what about Meter 4? If i do AB on meter 4 then it creates an unbalance....How do you resolve this?Are there any calculations that you can do to make sure all three phases are balanced..

Yes its a 208/120 3phase 4w incoming service to meter bank with main and then you have 208 1phase 3wire to each meter bank...
 

Smart $

Esteemed Member
I can understand the balancing concept of just alternating between 2 phases. But lets say you have a meter bank with 12 meters with 4 on each section.Now how do you balance two phases on each meter? A simpe technique is just have AB-Meter 1 ,BC-Meter 2,CA- Meter 3 but what about Meter 4? If i do AB on meter 4 then it creates an unbalance....How do you resolve this?Are there any calculations that you can do to make sure all three phases are balanced..

Yes its a 208/120 3phase 4w incoming service to meter bank with main and then you have 208 1phase 3wire to each meter bank...
Set up banks AB, BC, or CA... alternating banks. And each bank is single phase equipment rather than three phase.
 

shortcircuit1

Senior Member
Set up banks AB, BC, or CA... alternating banks. And each bank is single phase equipment rather than three phase.
I am sorry i didnt get that...
Are you saying set up AB BC CA horizontally three meter's then what about the the 4th meter socket?
 

shortcircuit1

Senior Member
Yes, it is.

If you have 65 units why not go with the 6-position branch units? See page 31 of this document if you are still going with the EZ Meter-Pak: http://download.schneider-electric.com/files?p_Reference=4100CT0701&p_EnDocType=Catalog&p_File_Id=7709686000&p_File_Name=4100CT0701.pdf

Phase balancing can be changed. See page 32.
Yes i can but there are some limitations that has to be met by POCO standards and clearances...I cant just pick 6 stack meter bank...And also there are space issues as well...I am trying to go with two meter banks with one meter bank feeding 32 units and other with 33 units...Have to consider the voltage drop as well...Thanks though..:thumbsup:
 

Smart $

Esteemed Member
Yes i can but there are some limitations that has to be met by POCO standards and clearances...I cant just pick 6 stack meter bank...And also there are space issues as well...I am trying to go with two meter banks with one meter bank feeding 32 units and other with 33 units...Have to consider the voltage drop as well...Thanks though..:thumbsup:
I understand. However, you did not acknowledge the part of my post about changing the phase balance. That should get you where you want to be.
 

wwhitney

Senior Member
I cant just pick 6 stack meter bank...And also there are space issues as well...I am trying to go with two meter banks with one meter bank feeding 32 units and other with 33 units...
So let's call it 33 units on each side, since that's a multiple of 3. I assume "stack" means a vertical section of meters, if you can't use 6 position stacks due to space constraints, do you want to use 3, 4, or 5? And does each stack get fed with 3 phases, or with just 1 phase (which alternates among stacks)?

3 position stack, 3 phases per stack: no problem, use 11 stacks per side.
3 position stack, 1 phase per stack: simplest would be to use 12 stacks per side, leave one blank space in each of the last 3 stacks.

4 position stack, 3 phases per stack: 9 stacks gives you enough spaces, but each stack will have one phase repeated. If the repeated phase is the same in each stack, then you'll be unbalanced. So you'll want adjustable stacks that let you change with phase gets repeated. You change 6 of the stacks, so that you end up with 3 stacks have two AB positions, 3 stacks having two BC positions, and 3 stacks having two AC positions.
4 position stack, single phase per stack: use 9 stacks, no problem, again leave one blank space in each of the last 3 stacks.

5 position stack, 3 phases per stack: 7 stacks give you enough spaces, but each stack will have one phase non-repeated. If the non-repeated phase is the same in each stack, then you'll be unbalanced. So again you'll want adjustable stacks, and you'll adjust 4 stacks so that 2 stacks have a single AB position, 2 stacks have a single BC position, and 2 stacks have a single AC position. The last stack will only have 3 meters, so just be sure those 3 are balanced.
5 position stack, 1 phase per stack: 7 stacks give you enough spaces, and the first 6 of those will result in a balanced system. The last stack with just 3 meters in it will be an issue, but that's the best you can do without buying 2 more stacks. Just be sure that this seventh stack is on different phases on each side. The system will be slightly unbalanced.

Cheers, Wayne
 

wwhitney

Senior Member
5 position stack, 1 phase per stack: 7 stacks give you enough spaces, and the first 6 of those will result in a balanced system. The last stack with just 3 meters in it will be an issue, but that's the best you can do without buying 2 more stacks. Just be sure that this seventh stack is on different phases on each side. The system will be slightly unbalanced.
Actually, you can buy 15 stacks total, put 7 on one side and 8 on the other, you'll end up with 10 empty spaces but can balance the system.

Cheers, Wayne
 

shortcircuit1

Senior Member
So let's call it 33 units on each side, since that's a multiple of 3. I assume "stack" means a vertical section of meters, if you can't use 6 position stacks due to space constraints, do you want to use 3, 4, or 5? And does each stack get fed with 3 phases, or with just 1 phase (which alternates among stacks)?

3 position stack, 3 phases per stack: no problem, use 11 stacks per side.
3 position stack, 1 phase per stack: simplest would be to use 12 stacks per side, leave one blank space in each of the last 3 stacks.

4 position stack, 3 phases per stack: 9 stacks gives you enough spaces, but each stack will have one phase repeated. If the repeated phase is the same in each stack, then you'll be unbalanced. So you'll want adjustable stacks that let you change with phase gets repeated. You change 6 of the stacks, so that you end up with 3 stacks have two AB positions, 3 stacks having two BC positions, and 3 stacks having two AC positions.
4 position stack, single phase per stack: use 9 stacks, no problem, again leave one blank space in each of the last 3 stacks.

5 position stack, 3 phases per stack: 7 stacks give you enough spaces, but each stack will have one phase non-repeated. If the non-repeated phase is the same in each stack, then you'll be unbalanced. So again you'll want adjustable stacks, and you'll adjust 4 stacks so that 2 stacks have a single AB position, 2 stacks have a single BC position, and 2 stacks have a single AC position. The last stack will only have 3 meters, so just be sure those 3 are balanced.
5 position stack, 1 phase per stack: 7 stacks give you enough spaces, and the first 6 of those will result in a balanced system. The last stack with just 3 meters in it will be an issue, but that's the best you can do without buying 2 more stacks. Just be sure that this seventh stack is on different phases on each side. The system will be slightly unbalanced.

Cheers, Wayne
That's good explanation.I was going to go with 2 meter banks with one meter bank feeding 32(4 stacks on each side) and 2nd meter bank with 33 units(4 stacks on one side and on other side 3 stacks having 4 meters per stack and the last stack one having 5 meters).
 

jumper

Senior Member
Is this one complex/building? If yes, aren't you going to need a common area meter and panel?
 

shortcircuit1

Senior Member
So let's call it 33 units on each side, since that's a multiple of 3. I assume "stack" means a vertical section of meters, if you can't use 6 position stacks due to space constraints, do you want to use 3, 4, or 5? And does each stack get fed with 3 phases, or with just 1 phase (which alternates among stacks)?

3 position stack, 3 phases per stack: no problem, use 11 stacks per side.
3 position stack, 1 phase per stack: simplest would be to use 12 stacks per side, leave one blank space in each of the last 3 stacks.

4 position stack, 3 phases per stack: 9 stacks gives you enough spaces, but each stack will have one phase repeated. If the repeated phase is the same in each stack, then you'll be unbalanced. So you'll want adjustable stacks that let you change with phase gets repeated. You change 6 of the stacks, so that you end up with 3 stacks have two AB positions, 3 stacks having two BC positions, and 3 stacks having two AC positions.
4 position stack, single phase per stack: use 9 stacks, no problem, again leave one blank space in each of the last 3 stacks.

5 position stack, 3 phases per stack: 7 stacks give you enough spaces, but each stack will have one phase non-repeated. If the non-repeated phase is the same in each stack, then you'll be unbalanced. So again you'll want adjustable stacks, and you'll adjust 4 stacks so that 2 stacks have a single AB position, 2 stacks have a single BC position, and 2 stacks have a single AC position. The last stack will only have 3 meters, so just be sure those 3 are balanced.
5 position stack, 1 phase per stack: 7 stacks give you enough spaces, and the first 6 of those will result in a balanced system. The last stack with just 3 meters in it will be an issue, but that's the best you can do without buying 2 more stacks. Just be sure that this seventh stack is on different phases on each side. The system will be slightly unbalanced.

Cheers, Wayne
Something like this.Its a 3phase 4wire incoming service and 1phase 3wire to residential units.
 

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