Balancing the load on a humongous apartment

[George Stolz]

I tend to tell stories with every bump in the road, so I'll keep this one short and sweet.

How critical is it to attempt to balance the loads on panelboards in a very large apartment building? Say, for example, there is a five story building, three floors of which contain 4 dwelling units a piece at the core. So, there are four feeders, supplying 3 panels apiece (feed through from floor to floor, vertically).

There are four additional wings, all supplied through their own 208Y/120v transformer, that fill out all five floors with dwelling units.

All five 208v transformers are supplied from the same 480v service.

Would you try to shift all the fixed appliances in each panelboard to different phases per floor? Would you shift the general purpose/lighting receptacles from floor to floor? Would you leave it to random chance for some items?

For this discussion, let's assume that the call is yours, and either the engineer has not specified a direction, or that you are the engineer, depending on what hat you normally wear.

 

[ItsHot]

load balancer

load balancer

Have the poco install one of those load balancing apparatus on their side!

 

[e57]

1. Why bother - odds are it will sort itself out anyway, explain in a moment....
2. You have no control of what the tenants will do.... What will be on and when.... And residential - most are non continuous...
3. Odds are most of the real big building loads are 3 phase....

Most of the stuff I do is POCO metered banks of meters... Poco delivers either 208/120 or 480 to thier own transformer to supply a second service if necesary. Then the meters I use split out 2 of 3 phases each to each unit, and most are roughly the same size and equipment. The meter banks are made just like this - First unit gets 1 and 2, and the next 2, and 3, the next 3 and 1, etc. Sounds like you're on bulk? Distribute single phase panels to each unit the same way. 1,2 - 2,3 - 3,1 All of the 3 phase stuff is equal, and you need to worry about balancing is single phase building equipment. (and that the tranformers are the right size...)

 

[George Stolz]

Thanks for the replies. The feeders moving upward through the building are 3? four-wire, as are the panelboards. So any option is possible at this point, in theory.

Keep 'em comin'...

 

[wireman71]

I'd just balance on calculated loads..

 

[celtic]

Considering the units are 1?208Y/120 feed from 3?480v...I would do nothing.

Say there are 9 units on three floors(just for the easy visual)

Flr 3:
Unit 1: A-B
Unit 2: B-C
Unit 3: C-A

Flr 2:
Unit 1: A-B
Unit 2: B-C
Unit 3: C-A

Flr 1:
Unit 1: A-B
Unit 2: B-C
Unit 3: C-A

If the branch circuits follow the same basic design in each unit, ie, electric ranges are always on ckts 9/11; AC on 5/7, etc...the average load per phase will be the same.


EDIT:
Each unit has a 3? panel???#4

 

[LarryFine]

Flr 1:
Unit 1: A-B
Unit 2: B-C
Unit 3: C-A

Wouldn't that be:
A-B
C-A
B-C
?

 

[celtic]

Wouldn't that be:
A-B
C-A
B-C
?

I suppose it could be....the last meter stack I did was 2 years ago :grin: ...I should remember as there were 90 meters :-?

In any case, the [calculated, not actual] loads balance.

 

[hmspe]

If I was designing this I'd probably set the first floor "as designed", move everything on the second floor down one breaker space (what was on breaker 1 goes on breaker 3), and move everything on the third floor down two breaker spaces (what was on breaker 1 goes on breaker 5). That's because it's all 3 phase. If it was single phase panels on a 3 phase system I wouldn't bother making any changes.

 

[e57]

Wouldn't that be:
A-B
C-A
B-C
?

Just check the meter pack that has been collecting dust in my basement - AB, BC, CA

But I yeah, suppose if coming out of panels it would be AB, CA, BC.... (Unless you skip a space on the other side of the panel....) But either way it is effective.

With all 3 phase in each unit (Something that I thought was not allowed untill corrected here a while ago.) I still don't think it will matter in the residential loads. So long as one of your guys doesn't decide that all of this will be that, and all of those will be this. 'all ovens black/red - all lighting blue...' Then you might have a problem, you would have to mix it up a bit.

 

[George Stolz]

Each unit has a 3? panel???#4

Yep. So essentially, visualize four 2" feeders running up each wing (one each, in the middle of each unit) hitting feed-through 3? panelboards the whole way up.

2. You have no control of what the tenants will do.... What will be on and when.... And residential - most are non continuous...

That was my take on it. I was curious how many people would keep close track of the home runs, and shift each floor a phase, and how many would simply allow the home runs to be randomly connected to the phases and let chance do the balancing, given the multitude of unknowns.

One other item that comes to mind: If the loads are imbalanced, what will effects can be expected, if the neutral is the same size as the ungrounded conductors?

 

[celtic]

Each unit has a 3? panel???#4

Yep. So essentially, visualize four 2" feeders running up each wing (one each, in the middle of each unit) hitting feed-through 3? panelboards the whole way up.

No problem on the visuals....I had written that whole thing then thought...did he say 1? or 3?? ....and I wasn't gonna re-write it

In that case, you'd probably need some attempt at balancing based on the calculated loads....resulting in adjusting some circuits...probably easiest to do so on a per floor (row) or coloumn basis.

 

[George Stolz]

Bump. ...............

One other item that comes to mind: If the loads are imbalanced, what will effects can be expected, if the neutral is the same size as the ungrounded conductors?

 

[iwire]

As you know the neutral must be sized for the maximum possible imbalance so even if it was smaller then the phase conductors it will be big enough.

I don't see any real issues for an EC to worry about with the premise wiring system.

However if the utility supply is marginally sized you will see the voltage becoming imbalanced as well....in a dwelling unit that will not be an issue....if you had 3 phase motors to much voltage imbalance makes the motors run hot.

Also a severe enough current imbalance might be noticed by the power company and in their service agreement will very likely be some wording about the maximum current imbalance they have to supply. They could force the customer to balance the load or they could terminate service.