Calculating percentage unbalance current in a panelboard/ system.

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jojo

Member
Location
Philippines
Occupation
Electrical Engineer
Hello, I just want to ask advice if I did this correctly. The system is 480Y/277V 3P, 4W having a phase currents: A=57.03amps (15.8kW), B=38.01amps (10.53kW) and C=38.93amps (10.78kW). Total connected load is 44.66amps (37.11kW). I want to know the percentage unbalance current.

Here's what I did:
% unbalance = [(maximum deviation from average)/ Average] x 100%
Average= (57.03A + 38.01A + 38.93A)/ 3 = 44.66A
Max deviation from average = 57.03A - 44.66A = 12.37A

%unbalance = (12.37A/ 44.66A)*100% = 27.70%

I know already that the max unbalance in the system/panelboard should be less than 10%. Please advise. Thanks in advance for your help. =)
 

robbietan

Senior Member
Location
Antipolo City
Hello, I just want to ask advice if I did this correctly. The system is 480Y/277V 3P, 4W having a phase currents: A=57.03amps (15.8kW), B=38.01amps (10.53kW) and C=38.93amps (10.78kW). Total connected load is 44.66amps (37.11kW). I want to know the percentage unbalance current.

Here's what I did:
% unbalance = [(maximum deviation from average)/ Average] x 100%
Average= (57.03A + 38.01A + 38.93A)/ 3 = 44.66A
Max deviation from average = 57.03A - 44.66A = 12.37A

%unbalance = (12.37A/ 44.66A)*100% = 27.70%

I know already that the max unbalance in the system/panelboard should be less than 10%. Please advise. Thanks in advance for your help. =)

that is correct.

however, I find it a bit strange that electrical systems use current unbalance as a limit for operation/safety. In the utility, we use the same formula to calculate for voltage unbalance (max of 2.5%)
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Balance is based on the connected loads, but there is no way to know what loads will be in use at any given time. There should be no operational issues or safety hazards even when you have load on only one phase.
 

jojo

Member
Location
Philippines
Occupation
Electrical Engineer
Correct, I agree with you don. It also won't happen that the loads will be utilize at the maximum, so there will be sort of load unbalance. But in load calculation, we are balancing it so that the loads are equally divided. That's why I thought of calculating % current unbalance.

Thanks don, I really appreciate your help.
 

tkb

Senior Member
Location
MA
I have tried this formula and don't see how multiplying it by 100% affects the result.
Shouldn't it be multiplied by 100 and not 100%?

Using 100% in Excel works when you format the cell as a percentage.
 
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jojo

Member
Location
Philippines
Occupation
Electrical Engineer
hello tkb. the reason we're multiplying it by 100% because the value of "[(maximum deviation from average)/ Average]" in the equation is in decimal. to change it to percent, we have to multiply it by 100.
 
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