[RE-wrenches] Sizing 3 phase OCPD - main

[Mark Frye]

Rebekah,
 
If you knew only the power and voltage, then you would use the root of 3 to
determine the amps. But since you know the amps, you don't need to use the
root.
 
The second equation would be the correct one.
 
Mark Frye 
Berkeley Solar Electric Systems 
303 Redbud Way 
Nevada City,  CA 95959 
(530) 401-8024 
 <http://www.berkeleysolar.com/> www.berkeleysolar.com  
 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Rebekah Hren
Sent: Wednesday, November 16, 2011 9:36 AM
To: RE-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] Sizing 3 phase OCPD - main


Hi wrenches, 


I have a question about sizing the main OCP breaker for a panel combining
the output of several true three-phase output inverters. To be precise - 10
of the  Refusol 20kW, which connect to  480V/277 Y with a max output of 24.1
amps, each inverter has a 3 pole breaker, line a, b, c and a neutral, which
doesn't apparently carry any current. 
Recommended interconnection breaker is 35 Amps. Ok fine, but what should the
main breaker and main panel busbar rating be? 
What I'm not sure about is if this is the right equation for the main
breaker in a panel combining all ten inverter outputs: 
10  x 24.1A x v3 x 1.25  = 521.8 A
or is this the right equation:
10 x 24.1A x 1.25 = 301.25 A
The busbar rating should be easy, once I get the main disco OCPD figured
out. 
Main OCPD + (10 x 35)  ? 120% busbar rating


Thanks for the help!
Rebekah Hren
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