PV combiner box protection [RE-wrenches]

[Phil Undercuffler]

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California Grid tie guy?  Man, Ray, that's hitting below the belt! ;-)

Actually, I live in Madrid, New Mexico--the closest thing this country has
to the third world next to Taos.  I've lost count of the systems I've done
for neighbors with next to nothing to their names.

But let's look at nuts and bolts.

Hypothetical situation:  Extremely poor couple, living in a bus.  300 watts
of array, 50 watt modules, pole mounted, 30'from batteries.  12v system
required, in order to run the stereo in the bus.

Using your proposal, 12-2 TC would run from each trio of daisy chained
modules to one of two QO breakers in a 2 pole NEMA 3 disconnect.  From
there,  #4 USE (no conduit in this neighborhood!) runs to a second
disconnect protecting the controller.

1 QO 3R box     60.01
1 QO indoor box 31.52
3 QO breakers   23.82
60' #4 wire     32.40
Total:          $147.75

My proposal:  12/2 tray cable from each module back to one of 6 input
breakers in a QO 6-12 disconnect mounted near the batteries, serving as
array disconnect and series fusing.

180' 12/2 TC    43.20
1 QO 6-12       40.01
6 QO breakers   47.64
Total:          $130.85

All prices dealer cost quoted from Summit Electric, a local supplier.
Neither proposal includes the 12/2 TC used for array wiring, nor do they
include controller overcurrent protection from the battery.  Wires sized for
3% voltage drop.

My point is not to beat a non-breathing equine, but to remind us all that
code compliant does not necessarily mean more expensive.

PS--beyond 300 watts, their array is larger than the one my wife and I lived
very nicely with, thank you very much, and their cries of poverty become
much dimmer in my ears.  And they should be 24 volts anyway.

Phil Undercuffler ext.238
Technical Support
phil at dankoffsolar.com

Dankoff Solar Products
    
The Premier Manufacturer and Distributor of Solar Water Pumps, and
Wholesale Distributor of Solar Electric, Wind, and Solar Heating Equipment

888-396-6611 toll free
505-473-3800 phone
505-473-3830 fax
www.dankoffsolar.com





on 6/24/04 11:53 AM, Ray Walters at ray at solarray.com 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.
> 

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