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<font size=3>Eric:<br><br>
Thanks for the research. I confess that I commented on an inverter
system I knew little about. My thanks to Darryl for keeping me
honest, and for the kind words. I had assumed that all modern
inverters are certified to prevent back feed, but this needs to be
checked for each new inverter.<br><br>
I'm not sure the language below is the same as an independent
verification that back feed will not occur. You may need to ask
your AHJ what they will accept.<br><br>
The limit on allowable back current is the fuse sizing specified by the
module manufacturer. This relates to how much fault current the
internal module wiring can handle before it fails (and possibly catches
fire).<br><br>
Humbly,<br><br>
William Miller<br><br>
<br><br>
<br><br>
At 07:42 PM 11/14/2010, you wrote:<br>
<blockquote type=cite class=cite cite>Thanks William and Daryl,<br><br>
Here is Auroras backfeed stipulation from the installation
manual:<br><br>
"Installation and Operator’s Manual Page 98 of 108<br><br>
(PVI-3.0/3.6/4.2-OUTD-x-US Rev: 2.1)<br><br>
<b>8.5 Input Source Backfeed Current</b><br><br>
PVI-4.2(3.6, 3.0)-OUTD-x-US Grid Tied Inverters are provided with two
separate and<br>
consecutive power stages:<br><br>
• Booster Stage (DC-DC converter) connected to DC Input Terminals.<br>
• Inverter Stage (DC-AC converter) connected to AC Output Grid
Terminals.<br><br>
The Booster Stage is provided with forward diodes that allows the current
(power)<br>
flow only from DC Input terminals towards Inverter (Output) Stage.<br>
In case of any fault on Inverter Stage, these diodes avoid any back-feed
current<br>
phenomena towards input terminals.<br><br>
In case of fault of the forward diode, the corresponding booster MOSfet
goes<br>
immediately and permanently in short circuit state and it avoids any
current<br>
propagation form output to input terminals.<br><br>
Abnormal Fault tests conducted during UL1741 qualification show also that
these type<br>
of faults produce the opening of internal grid disconnect relays and
cause the external<br>
AC CB protection devices to trip, preventing any power flow from the
grid.<br><br>
In conclusion for PVI-4.2(3.6, 3.0)-OUTD-x-US-y models it is not possible
to have<br>
any single fault responsible of Input source back-feed current flow. For
these models<br>
the Back-feed current into DC Source is negligible."<br><br>
According to this, the inverter will not backfeed even under most fault
conditions. My biggest concern is the four independent strings shorting
together somehow. I guess technically 4 strings of 8A for a total of 32A
doesn't exceed the ampacity of 10AWG XHHW-2....until you derate it for
roof temps. <br><br>
So whats the consensus?<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>
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<u>Please note new e-mail address and domain:<br><br>
</u>William Miller <br>
Miller Solar<br>
Voice :805-438-5600<br>
email: william@millersolar.com<br>
<a href="http://millersolar.com/" eudora="autourl">http://millersolar.com<br>
</a>License No. C-10-773985<br>
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