Another 3 phase load calculation question.

Merry Christmas

mike1061

Senior Member
Location
Chicago
I’m not confident I’ve done the service load calculation right. The catering place is in Chicago. It has a 3 phase 400 amp 240 volt service. The two 120 legs have a 400 amp fuse, while the high leg had a 250 amp fuse. He has blown mains before. The reason I’m involved is because he wants to add two more ovens, which are included in the the calculation. I’ve entered the data to a spreadsheet. I’ve taken all the amperage, voltage and phase from the name plates. Some don’t have one, so I guessed. I’ve entered the 120 volt on one leg only (volts x amps = volt amps . The 240 single phase Is entered volts x amps and entered one two legs. The 3 phase is volts x amps x 1.73 and is entered on all three legs. That is correct, right? On my trying to be balanced spreadsheet the highest leg is 167,685.2 volt amps. That would be equal to 1,397.37 amps. Even accounting for the two ovens that are not installed yet and the 2 va per square foot. How can he be operating without blowing mains every day? The coils for all the equipment is filthy and they run with little time off.
Can a couple people look at my calculation and see if it seems reasonable?
Thanks
Mike
 

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wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I’ve entered the 120 volt on one leg only (volts x amps = volt amps . The 240 single phase Is entered volts x amps and entered one two legs. The 3 phase is volts x amps x 1.73 and is entered on all three legs. That is correct, right?
Those are the correct calculations for total VA for each load, but I would think when entering the 240V single phase load on two legs, you enter half the total VA on each leg. Likewise for the 240V three phase loads on 3 legs, you enter one third on each leg.

Cheers, Wayne
 

mike1061

Senior Member
Location
Chicago
Those are the correct calculations for total VA for each load, but I would think when entering the 240V single phase load on two legs, you enter half the total VA on each leg. Likewise for the 240V three phase loads on 3 legs, you enter one third on each leg.

Cheers, Wayne
Thanks.
Edited to add:
So for the 3 phase I’d do, volts x amps x 1.73 divided by 3?
 
Last edited:

mike1061

Senior Member
Location
Chicago
Those are the correct calculations for total VA for each load, but I would think when entering the 240V single phase load on two legs, you enter half the total VA on each leg. Likewise for the 240V three phase loads on 3 legs, you enter one third on each leg.

Cheers, Wayne
I understand why. I just did some math examples. I’ve done that wrong every time so far. Man am I mad.
 
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