<div dir="ltr"><div>I look at batteries the same way as modules each string gets it own protection, its good for trouble shootings and for safety. we use the magnum Energy Class T fuse and holder, its cheap and works very well. If you have ever seen a short of a battery bank you would always install fuses right there at the bank and even just one bank <br>
</div>Jerry<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Feb 6, 2014 at 3:20 PM, Jason Szumlanski <span dir="ltr"><<a href="mailto:jason@fafcosolar.com" target="_blank">jason@fafcosolar.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_default" style="font-family:verdana,sans-serif">Allan's assessment matches my experience.</div>
<div class="gmail_default" style="font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif">
Interesting note: Outback's IBR enclosures include string-level overcurrent protection "for added safety" according to their data sheet.</div><div class="gmail_default" style="font-family:verdana,sans-serif">
<br></div><div class="gmail_default"><font face="verdana, sans-serif"><a href="http://www.outbackpower.com/downloads/documents/integrated_battery_rack/spec_sheet.pdf" target="_blank">http://www.outbackpower.com/downloads/documents/integrated_battery_rack/spec_sheet.pdf</a></font><br>
</div><div class="gmail_default" style="font-family:verdana,sans-serif"><br></div><div class="gmail_default"><font face="verdana, sans-serif"><a href="http://www.outbackpower.com/downloads/documents/integrated_battery_rack/integrated_battery_rack_installation_manual.pdf" target="_blank">http://www.outbackpower.com/downloads/documents/integrated_battery_rack/integrated_battery_rack_installation_manual.pdf</a></font><br>
</div><br><br><div><div style="font-size:13px;font-family:Verdana,Arial,Helvetica,sans-serif"><div style="margin:0px 0px 8px"><p style="margin:0px"><span><span>Jason Szumlanski</span></span><br>
</p><div style="clear:both"></div></div><img src="https://wisestamp.appspot.com/pixview.gif?p=chrome&v=3.31.0&t=1391728562839&u=eb875d38140ce271" height="1" width="1"></div></div><div><div class="h5"><div class="gmail_extra">
<br>
<br><div class="gmail_quote">On Thu, Feb 6, 2014 at 6:06 PM, Allan Sindelar <span dir="ltr"><<a href="mailto:allan@positiveenergysolar.com" target="_blank">allan@positiveenergysolar.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>Dave,<br>
I'm not really clear what your question is, but let me take a stab
at it anyway.<br>
<br>
Parallel strings of batteries are routine in PV systems; indeed,
far more common than single strings of large cells. Seldom are the
individual strings separately fused, and I have never seen it
required as a Code issue. The entire battery bank as a single
entity is considered a single current source. Overcurrent
protection is sized in accordance with the battery cable size - or
rather vice versa: the overcurrent protection is sized to the
requirements of the inverter(s) and the cables are sized to the
overcurrent protection.<br>
<br>
Having said that, there are at least two cases where it's a good
idea to account for it, whether or not addressed in the Code:<br>
1) In smaller systems, such as with two or three strings of common
batteries, you will eventually have a cell failure. When that
happens, the amps increase on the other remaining strings. So it
is good practice to oversize series and parallel interconnects for
that eventuality.<br>
2) For similar reasons, in large battery banks we have sometimes
added Class T fuses, appropriately sized to the application, to
the B+ output of each string before combining them on a bussbar.
These fuses serve only as catastrophic protection in case the
entire load tries to exceed the ampacity of one set of cells and
thus one set of cables.<br>
<br>
When we have done what I think you have described - two parallel
48V strings of 4 12V batteries each - we combine them with cables,
without additional string-level protection. That is in accordance
with manufacturers' instructions.<br>
<br>
Allan<br>
<br>
<div>
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<u></u>
<u></u>
<div>
<p class="MsoNormal"><b>Allan <span>Sindelar</span></b><br>
<span style="font-size:10pt"><a href="mailto:Allan@positiveenergysolar.com" target="_blank"><u><span style="color:rgb(0,0,153)">Allan@positiveenergysolar.com</span></u></a></span><br>
<span style="font-size:10pt">NABCEP Certified PV
Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder, <b>Positive Energy, Inc.<u></u><u></u></b></span></p>
<p class="MsoNormal"><span style="font-size:10pt">A
Certified B <span>Corporation<sup><span style="font-size:7.5pt">TM</span></sup></span><br>
<u></u><u></u>3209
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On 2/6/2014 3:23 PM, Dave Click wrote:<br>
</div></div></div><div><div>
<blockquote type="cite">All,
<br>
<br>
I think that in the past, list discussions have talked about
fusing of parallel battery circuits as a best practice, but it's
required per 690.9 right? (text below from 2008 NEC)
<br>
<br>
Also, if someone (don't look at me) really wants to use 2 parallel
circuits of 12V batteries, what equipment is recommended to
provide overcurrent protection? The installer is using Outback
hardware (FW500?) and has two battery circuits combined in the
battery enclosure and run to a Big Bus feeding the two 125A dc
disconnects for two GVFX3648s. If you've read this far, this area
is more your wheelhouse than mine. Thanks in advance!
<br>
<br>
<br>
690.9 Overcurrent Protection
<br>
(A) Circuits and Equipment. Photovoltaic source circuit,
photovoltaic output circuit, inverter output circuit, and storage
battery circuit conductors and equipment shall be protected in
accordance with the requirements of Article 240. Circuits
connected to more than one electrical source shall have
overcurrent devices located so as to provide overcurrent
protection from all sources.
<br>
<br>
Exception: An overcurrent device shall not be required for circuit
conductors sized in accordance with 690.8(B) and located where one
of the following apply:
<br>
(a) There are no external sources such as parallel-connected
source circuits, batteries, or backfeed from inverters.
<br>
(b) The short-circuit currents from all sources do not exceed the
ampacity of the conductors.
<br></blockquote></div></div></div></blockquote></div><br></div></div></div></div>
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