The QO breaker I saw fail was a disconnect switch for an Air
303. The run from the battery bank was substantial, and the wire was
number 10. At the time, I calculated the amperage available (I
-V/R) and the short circuit current available was not close to the
5000 amp AIC of the breaker for its DC rating.
At 06:13 PM 5/16/2010, you wrote:
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
sseveral 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.
On May 15, 2010, at 9:43 , Drake Chamberlin wrote:
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.
The 48v is a max rating not a nominal rating.
So yes only good for 12 and 24v systems.
However with CBI breakers I don't understand why the need for QO
for DC anymore?
jay
peltz power
On May 15, 2010, at 6:28 AM, Rebekah Hren wrote:
Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648
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Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648
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