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<div class="moz-cite-prefix">Hi Phil;<br>
<br>
I'm not sure what 690.71 adds over the long standing requirements
of 110.9 and 240.86. We've always complied with the interrupt
rating requirements. Old Ananda power centers had QOU breakers
that only had an interrupt rating of (I believe) 5000 amps DC, so
a class T fuse was added to the circuit as well. The power center
is always installed 'adjacent to the batteries', so we've always
met that requirement as well.<br>
Nothing in the NEC specifies an actual distance to the batteries
the OCPD needs to be, and it doesn't specify that each series
string have separate OCPDs. <br>
I'm glad to hear that Outback has a solution; Midnite has also had
that type of protection available in their battery enclosures for
some time as well. None of this deals with the truly high fault
currents available from industrial fork lift batteries though.
When using AGMs, you can just put a class T fuse on the battery
terminal.<br>
The only battery I've ever seen that actually protected against a
short circuit across its own terminals was in my kid's Barbie
Jeep. It had a fuse integrated right into the top of the sealed
battery. Maybe as the industry progresses towards other battery
chemistries, we will see more integrated OCPDs that are only found
on kid's toys today.<br>
<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 4/6/2013 8:29 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>
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