Ray,<div><br></div><div>690 does offer the protection, it's just that most maufacturers haven't made it easy.</div><div><br></div><div>690.71 Installation</div><div class="pa-70-2011-58-para" style="margin-top:3.6pt;margin-bottom:3.6pt">
<p class="pa-70-2011-58-para" style="margin-left:7.2pt;margin-top:1pt;margin-bottom:1pt"><font><span style="line-height:normal;background-color:rgba(255,255,255,0)"><span style="font-weight:bold">(C)</span> <span style="font-weight:bold">Current Limiting.</span> A listed, current-limiting, overcurrent device shall be installed in each circuit adjacent to the batteries where the available short-circuit current from a battery or battery bank exceeds the interrupting or withstand ratings of other equipment in that circuit. The installation of current-limiting fuses shall comply with 690.16.<span></span></span></font></p>
</div><div class="pa-70-2011-58-para" style="margin-top:3.6pt;margin-bottom:3.6pt"></div><div><br></div><div><div style>The telcom industry has been doing this for years. Their norm is to have each string of batteries on a shelf, and terminate at a breaker. Each string then is combined at a bus bar or plate, to help ensure equal current on each string. The loads and charging sources all come to that same bus bar. It has some advantages, as individual strings can be monitored and serviced without taking the entire system down.</div>
</div><div style><br></div><div style><div>FWIW, OutBack makes a battery rack for AGM batteries with series string overcurrent and disconnects on every string. It's also to my knowledge the first UL1741 Listed device available -- the other stuff I've seen is either not listed, or is trading on old 508a standards. AGMs might not be for every installation, but for jobs where they are appropriate this could be a good, code-compliant solution.</div>
</div><div style><br></div><div style><br></div><div style>Phil Undercuffler</div><div style>OutBack Power</div><div><br></div><div><br></div><div><br><br>On Friday, April 5, 2013, Ray Walters wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div>I just finished a rewire and we kept
the Ananda power center, Allan <span><span>
:-) </span></span><br>
Back when we used class T fuses more they were always over sized
relative to Heinemann breakers.<br>
400 amp class T fuse = 250 amp breaker= 4/0 cable<br>
200 amp class T fuse = 175 amp breaker= 2/0 cable<br>
<br>
I still think class T fuses are superior in some ways to breakers:
they have better interrupt capacity and trip faster in a short
circuit condition.<br>
<br>
However, If you spend too much time thinking about and looking at
the trip curves, you'll break your brain and special order some
weird fuses and breakers. (anybody need a 350 amp class T fuse?)<br>
Just follow the inverter manufacturer's recommendations and all
will be well.<br>
On the other hand, William has brought up a topic I have harped on
for years: Having the OCPD in the cabinet doesn't protect the
majority of the circuit. Class T fuses at the battery terminals
do, but they're not rated for the corrosive environment. I have
thrown a few class T fuses away that had acid eating away at the
ends.<br>
I don't have the solution, but I will continue to point out that
this is a real problem. Dropping a wrench across the battery
terminals can lead to a spectacular failure that not only can
cause a fire, but might even cause a battery explosion, yet NEC
offers no protection. <br>
We use insulated wrenches from experience, and hope for the best.
<br>
<pre cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 4/5/2013 8:29 PM, William Miller wrote:<br>
</div>
<blockquote type="cite">
Friends:<br>
<br>
Good topic. Some questions:<br>
<br>
1. Most manufacturer's present an installation guide that shows
one OCPD
in the battery circuit and that is in the BOS cabinet. This means
the battery leads are unprotected. Do we need an OPCD at the
battery terminals?<br>
<br>
2. Class T fuses are generally recommended for this application.
The data shows them as "fast acting." Is this a
problem? Will they act too fast and open during normal surge
loads?<br>
<br>
Thanks in advance!<br>
<br>
William Miller<br>
<br>
<br>
<br>
<br>
<br>
<blockquote type="cite">Troy,<br>
<br>
Overcurrent device size is matched to the conductor size. The
inverse
time constant nature of an overcurrent device can typically
handle the
surge currents as long as conductor sizing has truly been done
correctly
for the conductor. Circuit breakers are preferred to fuses
because they
can be reset. <br>
<br>
There has been volumes written on this issue. The constant
current at
lowest battery voltage should be used, plus the ac ripple
content on the
battery circuit. This is usually a much larger conductor than
your
average designer will plan for. The best thing is to look at
Midnight,
Outback, and Schneider and see what size overcurrent devices
they require
for their products. That will give you a good clue as to how to
size the
conductor and overcurrent device.<br>
<br>
Bill.<br>
<br>
<b>From:</b> <a href="javascript:_e({}, 'cvml', 're-wrenches-bounces@lists.re-wrenches.org');" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a href="javascript:_e({}, 'cvml', 're-wrenches-bounces@lists.re-wrenches.org');" target="_blank">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b>Troy Harvey<br>
<b>Sent:</b> Friday, April 05, 2013 3:38 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> [RE-wrenches] Fuse sizing in battery circuits<br>
<br>
I've got a question about battery string fusing. Typically we
size the
wire from the batteries to the inverter based on continuous
rating
procedures (max power/efficiency)*125%. <br>
<br>
However a 6kW inverter, can peak at 12kW for 5-10 seconds,
doubling the
source current. That is no big deal for the wire, because it is
a short
time frame... little heat will be generated. However, in fusing
the
sub-strings, you need to account for that peak surge current so
you don't
blow fuses all the time. But if you put a 500-1000 amp fuse on a
4/0
wire, above the max surge draw of the inverter, the wire will be
under-protected for its ampacity rating. Any thoughts on the
catch-22?<br>
</blockquote>
<br>
<fieldset></fieldset>
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