SIZING OF MAIN CIRCUIT BREAKER FOR A PANEL

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TMMB

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I have a panel board 220/380 V includes 28 Branch Circuit Breakers (controlling 28 Nos. FAN) , each FAN, 625 VA, 220 V, single Phase , the branch circuit breaker for each FAN is 20 A , how i can sizing the main circuit breaker for the panel board as per NEC
 
TMMB said:
I have a panel board 220/380 V includes 28 Branch Circuit Breakers (controlling 28 Nos. FAN) , each FAN, 625 VA, 220 V, single Phase , the branch circuit breaker for each FAN is 20 A , how i can sizing the main circuit breaker for the panel board as per NEC
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Sounds like three phase. 625va x 28ea / 220v / 1.73 = 45.9 total balanced amps per phase x 1.25 if they are running for 3 hours or more at a time. Plus whatever fudge factor you want to put on it for future expansion or unbalanced load.
 
Strathead said:
Sounds like three phase. 625va x 28ea / 220v / 1.73 = 45.9 total balanced amps per phase x 1.25 if they are running for 3 hours or more at a time. Plus whatever fudge factor you want to put on it for future expansion or unbalanced load.
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It's actually 380V three phase, or 17.5kVA/(380*1.73) = 26.6A

The 220 is phase to line voltage.
 
Darn it! :weeping: If I hadn't taken the extra time to make the 380 bold and red text, I would have posted first, and gotten all the credit. :lol:
 
Dears

My question: How i can sizing the main circuit breaker. take in consideration the demand factor for 28 nos. fans
 
There is no demand factor that would apply here. For all we know, all 28 fans could be running at the same time. But that does not really matter anyway. You have a load that is under 30 amps, and you have a need for 28 separate 20 amp breakers. You are not going to find a panel that has that many breakers and that has a rating any lower than 30 amps. So even if you could apply a demand factor, you will still need to get a panel rated 50 or 60 amps or more.
 
if the nos. of fans is 14 , what is the size of the main circuit breaker ?
 
We have shown you how to do the math. How about you telling us what you think the answer should be?
 
TMMB said:
if the nos. of fans is 14 , what is the size of the main circuit breaker ?
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You load would be closer to 13 amps. Keep in mind your motors are single phase
so at 14 your phases won't be evenly divided but you are still talking about a relative small main.

side note.. how do we justify the 20 amp breaker as a SCGF protector on an a 3 amp load ?
 
as per project specification the min. cable size can be used for each Fan is 4 mm2 (12 AWG), so we use 20 A to protect the cable and for fan there is normal protection
 
TMMB said:
as per project specification the min. cable size can be used for each Fan is 4 mm2 (12 AWG), so we use 20 A to protect the cable and for fan there is normal protection
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FWIW: IMO, your 20 amp breakers are oversized for short-circut-ground-fault protection as specified in 430.52
 
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