OCPD/Feeder Calc 3P

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Cletis

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Sorry, but this is a continuation from another thread. I was very rushed and posted the wrong info. Trying to size feeders and OCPD to a 3 phase sub panel to power these 2 machines. Here is correct info below

Machine 1 10,400VA (Actual Draw peak is 46amps/39amps)

Machine 2 10,400VA (Actual Draw same as above) Both 208V Single Phase

Phase A 10,400VA
Phase B 5,200VA
Phase C 5,200VA

Looking for below

Min Size Feeder
Min Size OCPD
 
As I recall in the other thread you had said nameplate values were 50A and 55A. Now you're saying 50A each.

Your A-phase VA is correct, but you can't divide by 2 where there isn't matching current from other phase. Currents are 86.6A, 50A, and 50A respectively.

Assuming neither is a continuous load, you're looking at #6CU/#4AL and 90A OCPD.
 
Using the VA the load is 50 amps which, according to my calculator, would give you a 87 amp load on the shared phase. Obviously, using your "amps" the load would be less.
 
Smart $ said:
As I recall in the other thread you had said nameplate values were 50A and 55A. Now you're saying 50A each.

Your A-phase VA is correct, but you can't divide by 2 where there isn't matching current from other phase. Currents are 86.6A, 50A, and 50A respectively.

Assuming neither is a continuous load, you're looking at #6CU/#4AL and 90A OCPD.
Click to expand...

Excuse the mess before. I was very hasty in posting the info, since then I sorted it all out and this is correct info.

Yes, would you mind posting your math on 86.6, 50, 50? I have a #1 Al 4 wire off a 3 pole 100 for 1 SET of machines, it's the other identical set we may be limited to a 90 3 pole off a #2 Al potentially I'm concerned about. 86.6A on a 90 is cutting it pretty darn close for me but with the lower actual readings of 46/39 and 214V at panel i'm thinking it may run a few amps less in reality. They are currently running on a number #8 Cu on 50 amp 2 pole breakers and they are running fine for years he said off those so
 
Been years since I'v done the math... I cheat & use a program that does it for me :)
As for the load, I appreciate your concern and would probably feel the same but keep in mind
(a) it's been running on a 50 amp breaker, (b) Code is "minimum" requirement but is supposedly safe. For comforts sake you might monitor the actual load for a short while.
It appears you might see some low numbers.
 
Cletis said:
Excuse the mess before. I was very hasty in posting the info, since then I sorted it all out and this is correct info.

Yes, would you mind posting your math on 86.6, 50, 50? I have a #1 Al 4 wire off a 3 pole 100 for 1 SET of machines, it's the other identical set we may be limited to a 90 3 pole off a #2 Al potentially I'm concerned about. 86.6A on a 90 is cutting it pretty darn close for me but with the lower actual readings of 46/39 and 214V at panel i'm thinking it may run a few amps less in reality. They are currently running on a number #8 Cu on 50 amp 2 pole breakers and they are running fine for years he said off those so
Click to expand...
The 50's are easy. There is no math involved.

The 86.6 is just 50A times square root of 3.
 
augie47 said:
Been years since I'v done the math... I cheat & use a program that does it for me :)
As for the load, I appreciate your concern and would probably feel the same but keep in mind
(a) it's been running on a 50 amp breaker, (b) Code is "minimum" requirement but is supposedly safe. For comforts sake you might monitor the actual load for a short while.
It appears you might see some low numbers.
Click to expand...

Wanna Share your program ?

How would loads change per phase if I land the 2-2pole breakers on 1(A),3(B),5(C),7(A) v.s. 1(A),3(B) and 2(A),4(B) (Phase C nothing)??
 
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