[RE-wrenches] AC breakers used in DC applications

[R Ray Walters]

I've also seen failures/ nuisance tripping due to loose connections at the breaker. The heat then wreaks havoc on the breaker internals.

R. Walters
ray at solarray.com
Solar Engineer




On May 17, 2010, at 8:23 AM, jay peltz wrote:

> HI Drake
> 
> I don't know if this could apply to your situation, but I've seen the QO/QOU fail from debris getting into the breaker itself.
> Around here there are insects that deposit mud into small openings, like on those breakers.
> I've seen this cause the breakers to fail.
> 
> jay
> 
> peltz power
> On May 17, 2010, at 7:02 AM, Drake Chamberlin wrote:
> 
>> 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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