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<div class="moz-cite-prefix">Phil,<br>
<br>
Thanks for the code references, they are very useful and point out
an area where I fear many installations of battery based inverters
are deficient. You are right the manufacturers have not made this
easy!<br>
<br>
First, data on the short circuit current available from most
batteries isn't easily available, if available at all. Concorde
publishes short circuit current numbers for the SunExtender
batteries. Neither Trojan, Rolls/Surrette, nor Outback publishes
short circuit current data for their batteries. Full River
publishes an internal resistance number that can be used to
estimate the short circuit current. Taken as a whole, battery
manufacturer's certainly haven't made it easy to comply with
690.71<br>
<br>
Second, sometimes interrupting capacity data on the breakers being
used in BOS equipment is also missing. Take a look at Outback's
catalog and try to find the AIC for the breakers used to protect
the inverter wiring. Is it published anywhere else? Should a
system designer have to buy the Outback breaker, find out who
manufactured it, and then search for the correct ratings in the in
the breaker manufacturer's catalog? Obviously not. <br>
<br>
Third, BOS manufacturers often connect circuit breakers for charge
controllers or dc utilization circuits that have AIC ratings of
only 5000 amps directly to the battery. So while the inverter may
be protected with a breaker having an AIC rating 25,000 or 50,000,
other devices don't. BOS manufacturer's should include on the dc
breaker panel data showing the <big>lowest</big> AIC breaker that
is connected directly to the battery. Then installers would have
at least half of the information needed to decide when a fuse is
needed to backup the dc breakers. And shouldn't the instructions
for BOS equipment point out that a fuse may be necessary at the
battery.<br>
<br>
The short circuit current from a single string of golf cart
batteries or L16 batteries is probably less than 5000 amps.
Fuse(s) are probably needed in most installations with larger
batteries or battery systems with multiple strings of batteries.
2011 NEC 240.21(H) allows overcurrent protection to be installed
as close as practical to battery terminals - even in classified
locations. <br>
<br>
<pre class="moz-signature" cols="72">Kent Osterberg
Blue Mountain Solar, Inc.
<a class="moz-txt-link-abbreviated" href="http://www.bluemountainsolar.com">www.bluemountainsolar.com</a>
</pre>
<br>
On 4/6/2013 7:29 AM, Phil Undercuffler wrote:<br>
</div>
<blockquote
cite="mid:CAPLQxEL9K1yPVccqJ0J671gy+JLZDGUvzhvupL_s9e3ymAf55Q@mail.gmail.com"
type="cite">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><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 moz-do-not-send="true"
href="javascript:_e({}, 'cvml',
're-wrenches-bounces@lists.re-wrenches.org');"
target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a moz-do-not-send="true" 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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