PV combiner box protection [RE-wrenches]

[Brad Bassett]

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Good thoughts about existing poorly wired systems. I'm sure there will 
be many posts about it. This post is about using QO breakers with 12 
volt systems. My experience is that the plug in breakers do not maintain 
good contact at 12v. I lived with a number of QO breakers and different 
load centers on my original 12 v system and I was constantly having to 
unplug and replug the breakers (or at least push them around a lot, it 
became a daily habit) to keep the contact adequate. Maybe a good dose of 
anti-ox would help? 

QOU feed through breakers (with screw lugs on both ends) are of course 
OK but don't fit the cheap standard load centers.

Brad


Solar Ray wrote:
> 
> Hi Phil;
> 
> All I can tell you is that many people are not going to be able to 
> afford 
> your way, and they're going to keep daisy chaining to infinity. I'm 
> trying 
> to offer a compromise that is safe and reasonable even if its not to 
> code. 
> 12 volt systems usually aren't to code anyway because so much of the 
> equipment( controllers, pumps, etc. are not
> UL listed) What I propose for these compromise systems is a  15 amp QO 
> breaker and box at the pole, array wiring with 12 -2 TC, and less than 
> 10 
> amps total array current per 15 amp breaker. We then bring the combined 
> current from the pole into the system with larger wire, again I size for 
> 
> ampacity and energy savings, not blindly to the 2% rule.(see my previous 
> 
> posts on wire sizing for watts lost, not voltage)
>   In poor communities, third world etc. this is light years beyond what 
> they are normally doing. I see salvage NMB wire twisted straight around 
> battery posts, etc.(no fuses, no controller) I'm not saying all you 
> California Grid tie guys should abandon the NEC, I'm just trying to 
> bring a 
> few of these really dangerous  out there systems under control. If some 
> retired person dies in a solar electric related fire, its going to look 
> bad 
> for all of us regardless of how poorly it was wired .
> Oh as an aside, the non-installer dealers are really contributing to 
> these 
> unsafe systems, by selling panels and batteries without any design help 
> or 
> fusing.
> 
> Bottom line: some fusing is better than nothing
> 
> Ray
> 
> PS If we really wanted to take care of the problem, we should push for 
> some 
> grant funding to go out and bring all these marginal systems into the 
> fold 
> before something happens. A little TLC now would be cheaper than a 
> damage 
> control PR campaign.
> 
> > >Come on, you're really going to bring
> > > each 50 watt module in a 12 volt system in on a separate wire and 
> > > breaker?
> > >
> > > Ray
> >
> >Yes, but not necessarily like you may think.  A 50 watt module = 3 amps 
> >at
> >12v.  That means #10 wire is good for about 50-60'.  In a system with 
> >less
> >than 2-300 watts of array, I'd consider running separate feeds back to a
> >Square D 6-12 box located at the power system (which could also serve as
> >array disconnect), or 1/4" ABC fuses at the array.  More array than 
> >that, or
> >the array run is further than 60'?  Consider adding MPPT.  And if you 
> >add
> >MPPT it's only a small jump to a higher voltage array.
> >
> >When you consider the cost of the raintight J-box at the array, the cost 
> >of
> >the splitbolts and splicing tape, and the labor getting a half-dozen 
> >wires
> >into that splitbolt and protected, and the labor it takes to undo that
> >splitbolt and splicing tape the first time you want to check module 
> >output,
> >I just don't see that much $$$ saved by eliminating the  series fusing.
> >
> >Phil
> 

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