[RE-wrenches] AC breakers used in DC applications

[Drake Chamberlin]

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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