[RE-wrenches] Sizing 3 phase OCPD - main

[Darryl Thayer]

Hi rebecca, I assume the inverters are all true 3 phase, to check 20 kW/480/1.73 = 24 amps this is what you expect on each leg.  You have 10 of these therefore 240 amps on each leg.  Solar is continous so you need x1.25 this is of course 301 amps you need to select a 301 breaker, but I think NEC 240.6 will allow a 300 amp.  ((sorry I do not have my code book and I am on the road))  
Good Luck
Darryl 


________________________________
From: Mark Frye <markf at berkeleysolar.com>
To: 'Rebekah Hren' <bekahhren at yahoo.com>; 'RE-wrenches' <re-wrenches at lists.re-wrenches.org>
Sent: Wednesday, November 16, 2011 11:43 AM
Subject: Re: [RE-wrenches] Sizing 3 phase OCPD - main


 
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 
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 √3 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 
_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20111116/f662a5cc/attachment-0004.html>