[RE-wrenches] how would you measure a partial short circuit

[Bill Brooks]

Nick,

 

How can you conclude that there was nothing wrong in regard to ground
faults. What was your reasoning that lead you to that conclusion. I think
there is doubt on your conclusion unless half the wiring in the second
string is backwards.

 

Bill.

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Nick Vida
Sent: Thursday, June 30, 2011 8:36 PM
To: wrenches
Subject: [RE-wrenches] how would you measure a partial short circuit

 

Hi wrenches.

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. 
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.
Do any of you have any thoughts on how one would measure for such a thing?

nick vida

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