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<br>
OK, nevermind... That'll teach me to respond before I know the
question even after reading it<br>
more than 3 times.<br>
<br>
For some reason I read the Voc's as being close in voltage as you
said here, Nick.<br>
<br>
But yes, 247V Vs. 437V would certainly cause a back feed !<br>
<br>
Must be late.<br>
<br>
boB<br>
<br>
<br>
<br>
<br>
<br>
On 7/1/2011 12:12 AM, boB Gudgel wrote:
<blockquote cite="mid:4E0D7378.6070909@midnitesolar.com" type="cite">
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On 7/1/2011 12:07 AM, boB Gudgel wrote:
<blockquote cite="mid:4E0D7232.80905@midnitesolar.com" type="cite">
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On 6/30/2011 11:35 PM, boB Gudgel wrote:
<blockquote cite="mid:4E0D6ABF.7030001@midnitesolar.com"
type="cite">
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On 6/30/2011 8:35 PM, Nick Vida wrote:
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cite="mid:1309491359.76072.YahooMailRC@web112306.mail.gq1.yahoo.com"
type="cite">
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<div style="font-family: Courier
New,courier,monaco,monospace,sans-serif; font-size: 12pt;">
<div>Hi wrenches.<br>
<br>
I had an interesting case today that I have been
thinking about since it happened. I dont have all the
details because the homeownter had to leave before I was
done with the service call, but here is what I do know.
SB5000 with 2 strings of 15 modules. String one was 437
vdc, and string 2 was 247vdc. I decided to look for a
ground fault, and I turned off the inverter. I measured
for ground faults and found no evidence of anything
wrong in that regard. As the homeowner was out of time
and wanted me to go, I re-landed the wires in the dc
disco, and when I replaced the fuses, I noticed a minor
arc when one of the fuses was going it. Although I had
no time to measure it, I think that there might be a
partial short circuit, possibly with one complete string
and some panels of the other string, and the remaining
panels on the second string. My mind was racing with how
I could have measured for a partial short circuit
without seeing it as an arch. I can imagine such a thing
on a bigger system being a dramatic electrical event. <br>
needless to say, I cant wait to get back there and go
through the signal path properly and find out what the
electrician did. And of course i realized that replacing
the fuses in such a questionable situation was probably
not the best idea.<br>
Do any of you have any thoughts on how one would measure
for such a thing?<br>
<br>
nick vida</div>
</div>
</blockquote>
<br>
<br>
"<span style="font-family: "Courier New";"> I
noticed a minor arc when one of the fuses was going it."<br>
<br>
</span></blockquote>
<br>
I see what you were saying. When the fuse was going "IN" ...
Into the fuse holder.<br>
<br>
Could it be that the inverter was connected (but turned off
otherwise) and it arced as the inverter input capacitors were
charging up ?<br>
<br>
If so, then the current would die to nothing soon after the fuse
was in place. A clamp meter would show<br>
that too.<br>
<br>
</blockquote>
<br>
<br>
ONE more thing on this... Because the strings were at slightly
different VOC's, it's possible that the<br>
higher Voc string will back feed the lower voltage string and you
may very well see a small arc if the fuse<br>
is connecting the two strings together. No ground fault needed
for that to happen.<br>
<br>
boB<br>
<br>
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