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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