how do you balance loads on a three phase feeder,feeding 13 subpanels?
- Thread starter zappy
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Then as Gus implied, you have three combinations of 120/208V 1? 3W: A-N-B, B-N-C, and C-N-A.
13 ? 3 = 4 whole + 1 remainder
...and you simply choose which combination you put the remainder on.
Is there a house panel wired 120/208V 1?? If there is, putting the "remainder" on a different combination will help the balancing.
beanland
Senior Member
- Location
- Vancouver, WA
Consider panel rating and load served
Consider panel rating and load served
Take it one step further because all panels are not created equal. If all the panels are 200A split-phase and carry the same load then 5-4-4 seems reasonable. But, to really balance the load, you want panel rating, or better yet, actual panel load, balanced.
Consider panel rating and load served
Take it one step further because all panels are not created equal. If all the panels are 200A split-phase and carry the same load then 5-4-4 seems reasonable. But, to really balance the load, you want panel rating, or better yet, actual panel load, balanced.
Good point!!!
copper chopper
Senior Member
- Location
- wisconsin
yea hard call to make, cheap fix is just to even the numbers out on each phase, expensive ( but the right way) is to get recording equipment and hook it up to each apartment to see what there amperage draw is and on what phases to really do the job right or if all the apt. owners are willing to give you a copy of there last 3 months electric bill you can find the largest usage that way.
Good idea.
Good idea.
No one is living in this building at the moment. Why is it that critical to balance the loads so precise?
Good idea.
No one is living in this building at the moment. Why is it that critical to balance the loads so precise?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
An electric bill will not show you how much current is on any one phase.
Trying to balance a panel in residential environments is at best going to get you in the ball park but it will not ever stay there as the loads will change at any given point in time, the best you could do is try to balance the heavy L-N loads across the phases as much as possible in each unit then as Augie pointed out, put the units 4,4,5 at the service gear if even possible as many meter packs will have the meters connected across the phase buss already.
Keep in mind that because of loads being single phase then the neutrals will always be considered as a current carrying conductor if any de-rating is done for conduits for multi-wire circuits.
Also any 240 volt heating appliances such as water heaters, dryers and ranges will be operating at lower kw ratings as well as any electric heating that is rated at 240 volts.
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hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
It's not, because it is almost impossible to get it exactly, but the utility just wants it as close as you can get it because they will size the transformer smaller then the load and if too much is placed across one set of phases it can cause the transformer to run hotter then normal which will shorten it's life, but they know you will not be able to get is perfect or will it stay there from time to time as loads are turned on and off.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If all of the apartments are relatively the same then I agree with Hurk it's not and any attempt beyond Gus's suggestion (5-4-4) is futile. It's possible that at any given time one or more apartments will be empty and have no load at all.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
If the units are independently metered, thinking about how to divvy up the loads is not required. Modular meter stacks do it for you.
- Location
- Massachusetts
More precisely the guy ordering them has decided for you. You can order them as needed if you had some sort of odd loads.
But I do agree with you, all the ones I have worked with simply rotated the pairs evenly as possible.
kwired
Electron manager
- Location
- NE Nebraska
It is not in most cases. If the supply has limitations then it can be critical. You could have a case where utility can tolerate more imbalance but maybe a back up source can not. There does become a point where you do not want to have too much imbalance either. Say you have all the load on two phases - then you likely need larger panels, conductors, transformers, etc than if you had the load balanced or at least close to being balanced over three phases.
50 KVA balanced over three phases of a 120/208 is about 139 amps per phase. If you put same load across only two phases you will draw 240 amps per phase.
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