[RE-wrenches] Head Spinning..(Con) fused.

Dave Click daveclick at fsec.ucf.edu
Sun Nov 14 17:20:41 PST 2010


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 <william at millersolar.com>
To: RE-wrenches <re-wrenches at 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 /<william at millersolar.com>/* wrote:
>>>
>>> From: William Miller <william at millersolar.com>
>>> Subject: Re: [RE-wrenches] Head Spinning..(Con) fused.
>>> To: "RE-wrenches" <re-wrenches at 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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>>> _Please note new e-mail address and domain:
>>>
>>> _William Miller
>>> Miller Solar
>>> Voice :805-438-5600
>>> email: william at millersolar.com
>>> http://millersolar.com
>>> <http://millersolar.com/>License No. C-10-773985
>>>
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>>
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>
> _Please note new e-mail address and domain:
>
> _William Miller
> Miller Solar
> Voice :805-438-5600
> email: william at millersolar.com
> http://millersolar.com
> <http://millersolar.com/>License No. C-10-773985
>
>
>
> _______________________________________________
> List sponsored by Home Power magazine
>
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