PV combiner box protection [RE-wrenches]
Ray Walters
ray at solarray.com
Thu Jun 24 10:53:56 PDT 2004
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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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