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

[Darryl Thayer]

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

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