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On 6/30/2011 10:48 PM, Marv Dargatz wrote:
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<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">Come on, Bob.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
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color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">It’s a ground fault in the
array. Just one more example why ungrounded arrays are
FAR safer.<o:p></o:p></span></p>
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<br>
<br>
Could also possibly disconnect the arrays at both ends and use a
voltmeter<br>
to measure resistance to ground to find it if that's what the
problem is.<br>
<br>
Or use a current limited supply and measure voltage drops to zoom in
on the problem.<br>
<br>
boB<br>
<br>
<br>
<br>
<br>
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<p class="MsoNormal"><span style="font-size: 10pt;
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<p class="MsoNormal"><span style="font-size: 10pt;
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color: rgb(31, 73, 125);">Marv<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt;
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Support, North America<o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="font-size: 10pt;
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"Calibri","sans-serif"; color:
rgb(31, 73, 125);">SolarEdge Technologies, Inc.<o:p></o:p></span></b></p>
<p class="MsoNormal"><span style="font-size: 11pt;
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+530.798.6770<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size: 10pt;
font-family:
"Tahoma","sans-serif"; color:
windowtext;">From:</span></b><span style="font-size:
10pt; font-family:
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windowtext;">
<a class="moz-txt-link-abbreviated" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a class="moz-txt-link-freetext" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On
Behalf Of </b>boB Gudgel<br>
<b>Sent:</b> Thursday, June 30, 2011 10:19 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Cc:</b> Nick Vida<br>
<b>Subject:</b> Re: [RE-wrenches] how would you
measure a partial short circuit<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">On 6/30/2011 8:35 PM, Nick Vida wrote: <o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom: 12pt;"><span
style="font-family: "Courier New";">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<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom: 12pt;"><br>
I'd probably use a DC clamp on ammeter. Clamp on and
measure the top and bottom current of each string... What
comes in ~should~ come out.<br>
<br>
If it's much different on one end vs. the other end of one
string, maybe that string is conducting around the path
somehow. Remember that<br>
sometimes just turning the clamp around and measuring the
opposite polarity may measure slightly differently than the
opposite polarity and<br>
that zero calibration is usually necessary.<br>
<br>
boB<br>
<span lang="JA">鮑勃</span> <br>
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