Fronius IG Plus on the spec sheet also specs "Max. continuous utility
back feed current" as 0A.
-------- Original Message --------
Subject: Re: [RE-wrenches] Head Spinning..(Con) fused.
From: William Miller <will...@millersolar.com>
To: RE-wrenches <re-wrenches@lists.re-wrenches.org>
Date: 2010/11/14 12:54
Darryl:
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.
I think SMA is not the only transformer inverter with a no-backfeed
declaration.
William
At 05:48 AM 11/14/2010, you wrote:
I never thought I would disagree with William, I have the highest
admiration for him,
But the transformerless inverter has no seperation between grid and
array, no problem if everything is fused.
Darryl
--- On *Sat, 11/13/10, William Miller /<will...@millersolar.com>/* wrote:
From: William Miller <will...@millersolar.com>
Subject: Re: [RE-wrenches] Head Spinning..(Con) fused.
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Date: Saturday, November 13, 2010, 11:26 PM
Eric:
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.
The general rule is no system with two strings combined needs fuses.
Run the calcs as presented in the white paper for verification.
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.
William Miller
At 08:40 PM 11/13/2010, you wrote:
Wrenches,
Can anyone shed guidance on the following for me? Should these
strings be fused:
Total Modules: 44
Total Strings: 4 strings of 11
Total Inverters: 2
Modules: Silicon Energy 195 Watt @ 8A
Each string feeding an independent MPPT input on an Aurora PVI 4.2kW
Inverter (there are 2 / Aurora)
Inverter is transformerless (READ 690.35 (B))
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.
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."
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?
Or am I just up too late reading code....?
Thanks for being a resource.
--
Eric Thomas
Solar Epiphany LLC
(206) 919-3014
www.solarepiphany.com <http://www.solarepiphany.com/>
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