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 <ma...@berkeleysolar.com>
To: 'Rebekah Hren' <bekahh...@yahoo.com>; 'RE-wrenches'
<re-wrenches@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-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Rebekah
Hren
Sent: Wednesday, November 16, 2011 9:36 AM
To: RE-wrenches@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
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