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<font size=3>Darryl:<br><br>
If Aurora can not verify that their inverters will not backfeed the DC
circuitry, then the circuits must be fused. This too is specified
in Berdner's study. We are in agreement.<br><br>
I think SMA is not the only transformer inverter with a no-backfeed
declaration.<br><br>
William<br><br>
<br><br>
At 05:48 AM 11/14/2010, you wrote:<br>
<blockquote type=cite class=cite cite>I never thought I would disagree
with William, I have the highest admiration for him, <br>
But the transformerless inverter has no seperation between grid and
array, no problem if everything is fused. <br>
Darryl<br>
--- On <b>Sat, 11/13/10, William Miller
<i><william@millersolar.com></i></b> wrote:<br>
<blockquote type=cite class=cite cite><br>
From: William Miller <william@millersolar.com><br>
Subject: Re: [RE-wrenches] Head Spinning..(Con) fused.<br>
To: "RE-wrenches"
<re-wrenches@lists.re-wrenches.org><br>
Date: Saturday, November 13, 2010, 11:26 PM<br><br>
Eric:<br><br>
The best resource I have found on this subject is the white paper that
John Berdner wrote. I have a copy on my web site: millersolar.com
under Resources.<br><br>
The general rule is no system with two strings combined needs
fuses. Run the calcs as presented in the white paper for
verification.<br><br>
Just because circuits share a J-box or conduit is not a reason to
fuse. Actual connection into an inverter is required before the
number of strings is tabulated.<br><br>
William Miller<br><br>
<br><br>
<br>
At 08:40 PM 11/13/2010, you wrote:<br>
<blockquote type=cite class=cite cite>Wrenches,<br><br>
Can anyone shed guidance on the following for me? Should these strings be
fused:<br><br>
Total Modules: 44<br>
Total Strings: 4 strings of 11 <br>
Total Inverters: 2<br><br>
Modules: Silicon Energy 195 Watt @ 8A<br>
Each string feeding an independent MPPT input on an Aurora PVI 4.2kW
Inverter (there are 2 / Aurora)<br>
Inverter is transformerless (READ 690.35 (B))<br><br>
Each strings passes through a shared SolaDeck jbox, no combining, and
head directly to their own dedicated GE THN2261RDC DC Disconnect before
entering a dedicated MPPT input on the inverter.<br><br>
My big question is 690.9 (A) exception (b) which states I don't need ocpd
as long as "The short circuit currents from all sources do not
exceed the ampacity of the conductors."<br><br>
Because all four strings pass through the same jboxs and conduit before
reaching their disconnect and could potentially short together, should I
fuse each string? <br><br>
Or am I just up too late reading code....?<br><br>
Thanks for being a resource.<br><br>
-- <br>
Eric Thomas<br>
Solar Epiphany LLC<br>
(206) 919-3014<br>
<a href="http://www.solarepiphany.com/">www.solarepiphany.com</a><br><br>
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19:34:00</blockquote><u>Please note new e-mail address and
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<u>Please note new e-mail address and domain:<br><br>
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