Higher than 48 nom Arrays (was Different perspectives,) [RE-wrenches]

[Christopher Freitas --- OutBack Power]

There are actually several different ratings on the OBPV breakers we use 
in our PSPV combiner boxes. The one printed on the front is just one of 
its multiple listings.  

The 80 vdc 7500 amp interrupt rating is the UL489 approval - essentially 
the "branch circuit" rating for use as a load breaker or other general 
purpose application.  This is a pretty tough standard for breakers. It 
applies to use of the breaker with battery systems for instance.  

The combiner box is actually what is called a supplementary application 
- meaning the UL489 approval of the breakers is not required.  In this 
case a lower rating for interrupt is acceptable.  The applicable rating 
for this application is the 125 vdc 2000 amp rating that is marked on 
the side of the breaker.  Even this rating is overkill as the PV array 
can not produce anything near these kinds of currents - PV is a pretty 
wimpy power source from a breaker perspective. 

As far as using these breakers with 72 vdc applications - I have no 
problem with it - even though the open circuit voltage of the PV array 
in cold temps can exceed 125 vdc - these breakers will handle it - and 
the factory testing I have reviewed and personal experience with these 
breakers confirms this.

Also - its funny how we as an industry are concerned with exceeding the 
125 vdc rating on a DC breaker by a few volts - but we think nothing of 
exceeding the 120 VAC rating on AC breaker with a generator putting out 
140 vac unloaded?  Seems strange hugh?  Even a utility grid can be 132 
vac (especially when an inverter is backfeeding the breaker as in a 
grid-tie application). 

I guess it must be that the PV output is more dangerous than AC power 
from a utility grid?

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com  
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030  


Travis Creswell wrote:
> I must admit that I'm a little nervous about wiring the array for 72
> volts.  Could you address the issue of the Outback's DC breakers AIC
> rating of 7.5k amps at 80 volts.  What is the AIC rating at 105 or
> higher?  This is an easily attainable MPP voltage during cold weather.
> I've seen solar equipment supposedly rated at 125 VDC fail at 100 volts
> or less is why I ask.

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