Total Load Calculation on existing building

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jscott615

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Hi-

I am trying to calculate the total load on a building. The building is using a 208/120 3PH 4W system. A phase is drawing 42A on the primary feeder. B phase is drawing 63A. C phase is drawing 30A.

To me, it seems you just add A+B+C and you get the total for the building. However, I have seen all kinds of formulas using power factors and other variables. I am just starting to learn more about theory, and I want to make sure I learn the right way.

Thanks for any help, it's greatly appreciated.
 
jscott615 said:
Hi-

I am trying to calculate the total load on a building. The building is using a 208/120 3PH 4W system. A phase is drawing 42A on the primary feeder. B phase is drawing 63A. C phase is drawing 30A.

To me, it seems you just add A+B+C and you get the total for the building. However, I have seen all kinds of formulas using power factors and other variables. I am just starting to learn more about theory, and I want to make sure I learn the right way.

Thanks for any help, it's greatly appreciated.
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I suggest you read 220.87 NEC 2008 if you do not know what equipment and loads are already in there. This tells you how to determine existing loads.
 
jscott615 said:
Hi-

I am trying to calculate the total load on a building. The building is using a 208/120 3PH 4W system. A phase is drawing 42A on the primary feeder. B phase is drawing 63A. C phase is drawing 30A.

To me, it seems you just add A+B+C and you get the total for the building. However, I have seen all kinds of formulas using power factors and other variables. I am just starting to learn more about theory, and I want to make sure I learn the right way.

Thanks for any help, it's greatly appreciated.
Click to expand...

I was ready to respond until I saw you said you wanted to learn the right way, in case I give you some bad money forgive me. Normally with recorded meter readings lets say for a day or more you can get an accurate picture of th electrical activity in the building. In your case with those measurements, we see that we have an unbalanced system but we can still make an assumption. Since your B phase is most loaded lets assume if the system were balanced all the phases would be loaded similarly 63A. From there you can calculate KVA. Other ways I have seen some do is to average the currents on each phase then calculate KVA.
 
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