Metering calculation question

[cdw238]

Recently had a 480Y/277-volt, three-phase, four-wire feeder metered for one week. The following were the maximum load readings at each of the phases metered at 277-volts each.

Phase A (metered voltage 277-volts): 356A, 99.5 kVA Apparent Power
Phase B (metered voltage 277-volts): 309.5A, 85.7 kVA Apparent Power
Phase C (metered voltage 277-volts): 331A, 92.3 kVA Apparent Power

Power factor was right around 0.85 for each phase.

What is the correct way to calculate the overall load on the 480Y/277-volt system?

If I add together the three values for apparent power, I come up with a total of approximately 277.5 kVA for the 480-volt, 3-phase, 4-wire feeder which gives me approximately 333.8 Amps. I get this by the following:

227.5 kVA / 480-volts/ (sqrt of 3)

Is this correct?

 

[mull982]

Yes your calculations are correct

 

[markstg]

Recently had a 480Y/277-volt, three-phase, four-wire feeder metered for one week. The following were the maximum load readings at each of the phases metered at 277-volts each.

Phase A (metered voltage 277-volts): 356A, 99.5 kVA Apparent Power
Phase B (metered voltage 277-volts): 309.5A, 85.7 kVA Apparent Power
Phase C (metered voltage 277-volts): 331A, 92.3 kVA Apparent Power

Power factor was right around 0.85 for each phase.

What is the correct way to calculate the overall load on the 480Y/277-volt system?

If I add together the three values for apparent power, I come up with a total of approximately 277.5 kVA for the 480-volt, 3-phase, 4-wire feeder which gives me approximately 333.8 Amps. I get this by the following:

227.5 kVA / 480-volts/ (sqrt of 3)

Is this correct?

the overall maximum load on the system is 277.5 KVA as you have shown. But the current value of 338.8 A is the average amps of the system, as your measurements show A phase takes more, the others less. If your trying to add load, be careful about overloading phase A, even though phase B and C may not get overloaded.