Eric:
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.
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.
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).
Humbly,
William Miller
At 07:42 PM 11/14/2010, you wrote:
Thanks William and Daryl,
Here is Auroras backfeed stipulation from the installation manual:
"Installation and Operators Manual Page 98 of 108
(PVI-3.0/3.6/4.2-OUTD-x-US Rev: 2.1)
8.5 Input Source Backfeed Current
PVI-4.2(3.6, 3.0)-OUTD-x-US Grid Tied Inverters are provided with two
separate and
consecutive power stages:
Booster Stage (DC-DC converter) connected to DC Input Terminals.
Inverter Stage (DC-AC converter) connected to AC Output Grid Terminals.
The Booster Stage is provided with forward diodes that allows the current
(power)
flow only from DC Input terminals towards Inverter (Output) Stage.
In case of any fault on Inverter Stage, these diodes avoid any back-feed
current
phenomena towards input terminals.
In case of fault of the forward diode, the corresponding booster MOSfet goes
immediately and permanently in short circuit state and it avoids any current
propagation form output to input terminals.
Abnormal Fault tests conducted during UL1741 qualification show also that
these type
of faults produce the opening of internal grid disconnect relays and cause
the external
AC CB protection devices to trip, preventing any power flow from the grid.
In conclusion for PVI-4.2(3.6, 3.0)-OUTD-x-US-y models it is not possible
to have
any single fault responsible of Input source back-feed current flow. For
these models
the Back-feed current into DC Source is negligible."
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.
So whats the consensus?
--
Eric Thomas
Solar Epiphany LLC
(206) 919-3014
<http://www.solarepiphany.com>www.solarepiphany.com
_______________________________________________
List sponsored by Home Power magazine
List Address: [email protected]
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
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8.5.449 / Virus Database: 271.1.1/3257 - Release Date: 11/14/10
19:34:00
Please note new e-mail address and domain:
William Miller
Miller Solar
Voice :805-438-5600
email: [email protected]
http://millersolar.com
License No. C-10-773985
_______________________________________________
List sponsored by Home Power magazine
List Address: [email protected]
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
