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

[William Miller]

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
>>><http://www.solarepiphany.com/>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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Please note new e-mail address and domain:

William Miller
Miller Solar
Voice :805-438-5600
email: william at millersolar.com
http://millersolar.com
License No. C-10-773985
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