TCB10 Failure was (QO Breakers and Panels) [RE-wrenches]

[Travis Creswell, Ozark Solar]

Bill has a point here. And I have was I suspect is evidence but the doesn't
release Pulse from what appears to be a manufacturing defect.  They or Trace
still owes me a new combiner box!  Maybe I applied it wrong and I can accept
that but hopefully all of us can learn from it.

This summer I reworked a battery less water pumping system for the USFS. 
The array consisted of twenty 50 watt DuraVolts which basically are Kyocera
LA51's with a stainless steel back and a clear tedlar front instead of
glass.  There was 4 sets of 5 in series.  Power point voltage is right at 85
volts but the system almost always runs at 75 volts due the AY McDonald pump
controller.  OCV @ 77F is 21.2x5=106 volts, SSC is < than 13 amps.  This is
from various spec sheets that I have found and some of you sent me.  On a
side note it turned out we were dealing with 2nd generation models and they
did not have the high failure rate (100%) of the originals.

Back to the failure part of the story.  I didn't see it happen but the
combiner box that I added caught on fire.  The system had no combiner box
lightning protection before that point. The fire appears to have started on
the back and last for a while.  It was still sparking/smoking when the USFS
employee checked on it.  He had to cut the wires in the pull boxes near the
base of the trackers to stop it.  No signs of lightning damage anywhere. 
The LA-302-DC is shows no external damage nor does the TVSS (ZNR's) built
into the terminal board of the TCB10.

This device is rated for 125 volts DC.  I installed the TCB10 combiner box
in mid summer and it failed by  early fall.  From that it can be assumed
that it never got anywhere near cold enough to get the OCV of the array up
to 125v.  I emailed JPG.s to Allen Lowe of Trace and he had no idea what
happened and suggested maybe a loose wire.  I don't think that was it as the
fire started on the back of the board.  

A Pulse rep. who no longer works there but was the only person from Pulse I
could get with.  He is on this list and I let him identify himself if he
wants to but you all probably already figured out.  His reply was that the
unit was designed for 4 modules in series not 5 and so he felt the over
voltage got it.  But I don't think so as I don't see how the volts got
anywhere near 125.

And please feel free to tell me I misapplied it along with the definition do
we can all learn from my mistake.

Travis Creswell
Ozark Solar
----------
>From: Bill Brooks <billbrooks7 at earthlink.net>
>To: RE-wrenches at topica.com
>Subject: RE: QO Breakers and Panels [RE-wrenches]
>Date: Tue, Mar 6, 2001, 10:43 PM
>

 One of the real hazards we have is
>counter-intuitive--since we have a limited current source (PV array) it does
>not tend to fuse wires and do things as are cited below. It just burns and
>burns until there is not longer any fuel. It can take a long time to use up
>all the fuel in many systems were we have plastics and EVA and wire
>insulation, etc....

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