<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Small (QO or Airpax-type) breakers in a distribution bank should be front ended with a suitable DC master breaker or fuse that has the capability to interrupt the available fault current. Ideally, the series combination should be rated but at a minimum, a coordination study should be undertaken.</div><div><br></div><div>I like to have primary protection on each string, as close to the battery as possible - preferably bolted to the battery terminal. Cable limiters are nice, but a TPL style fuse is easier to get.</div><div><br></div><div><br></div><br><div><div>On May 16, 2010, at 16:13 , Kurt Albershardt wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Voltage is not the issue here, it is current, and battery fault currents can be staggering - far more than one would ever encounter in a typical AC system fed from a distribution transformer. I have seen a 200A Class T fail to act on an 48V inverter fault which resulted in welding the metal tabs of the fuse holder (which had been greased with copper-laden Penetrox E) to their sockets. That indicates a fault current well north of 200,000 amps, quite possibly several times that. A fire ensued, which triggered the gas protection system and fortunately resulted in almost no peripheral damage. It did cost about $10k to recharge and recertify the Inergen system. The inverter manufacturer was quite cagey on warranty replacement until they saw the photos - at which point a replacement miraculously arrived by overnight air.</div><div><br></div><div><br></div><br><div><div>On May 15, 2010, at 9:43 , Drake Chamberlin wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>
I did see a QO breaker fail to trip on a 24 volt DC system with only
battery voltage behind it. It burned a #12 wire completely in
two. <br><br>
<br>
<blockquote type="cite" class="cite" cite="">The 48v is a max rating not a
nominal rating.<br>
So yes only good for 12 and 24v systems.<br><br>
However with CBI breakers I don't understand why the need for QO for DC
anymore?<br><br>
jay<br><br>
peltz power<br>
On May 15, 2010, at 6:28 AM, Rebekah Hren wrote:<br>
</blockquote>
<x-sigsep><p>
<font color="#0000FF">Drake Chamberlin<br>
Athens Electric<br>
OH License 44810<br>
CO License 3773<br>
NABCEP </font><font size="1" color="#0000FF">TM
</font><font color="#0000FF">Certified PV Installer <br>
Office - 740-448-7328<br>
Mobile - 740-856-9648</font></p></x-sigsep></div></blockquote></div></div></blockquote></div></body></html>