More String fusing: Fronius 5100 [RE-wrenches]

[Phil Undercuffler]

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William, 

The driving factors in series fuse/no series fuse is the number of strings
and module choice, not inverter.

For instance if using Sanyo 190 modules, which have a 3.75A Isc output and
15 amp series fuse rating, you can run 4 strings of modules without
requiring series fusing.  However, use BP 3125S modules (7.54A Isc and 15A
fuse rating) and you can only run 2 strings before triggering the series
fuse requirement.

This is allowed by NEC 690.9(A), Exception B.

John Wiles wrote a short paper on PV modules and series overcurrent devices
that explains more, although it can make your eyes cross.  Anyone that wants
it, request off list and I'd be glad to send a copy.  Also, Brian Farhi at
Fronius wrote a very handy fuse sizing Excel reference tool that I use
almost daily. 

Phil Undercuffler
Technical Support, ext. 238
p.undercuffler at conergy.us
 
Conergy Inc.
 
888-396-6611 toll free
505-473-3800 phone
505-473-3830 fax
www.conergy.us
 

-----Original Message-----
From: William Miller [mailto:wrmiller at slonet.org] 
Sent: Wednesday, August 03, 2005 2:21 AM
To: RE-wrenches at topica.com
Subject: More String fusing: Fronius 5100 [RE-wrenches]

Friends:

New project:  Bidding on a Fronius 5100 install.  It says right in the
manual that you can connect up to 3 strings to the 5100 (and other models,
and up to 4 strings in even other models).  I see no fuses in the pictures.
Isn't this an NEC violation?????

William Miller

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