[RE-wrenches] Finding ground faults

[Darryl Thayer]

Bob I had a tough find one time, when it rained I would have GF when it would dry out no GF 
I turned off main DC disconnect, I turned off each circuit breakers for the strings, I opened the grounded conductor of the strings, I connected my Megger at 500 volts I think It might have been maybe 1000 volts, after the fault cleared, the megger found one string that was bad and I located the problem in a J box 
 

________________________________
 From: Steve Higgins <shiggins at outbackpower.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org> 
Sent: Wednesday, May 23, 2012 11:27 AM
Subject: Re: [RE-wrenches] Finding ground faults
  

 
Bob,  
  
Be careful with that GFDI... It's most likely wired on the output of the controllers, on the battery side.   
  
This can trip if a ground fault is occurring, or if you are exceeding 80 amps of current.   With 8, 3 module strings, an edge of cloud event you could have the 80amp portion of that breaker tripping rather than the GFDI.  
  
Steve Higgins 
Sales Application Engineering Mgr 
Direct 360-618-4313 
Outback Power Technologies  
5917 195th Street NE Arlington, Washington 98223 
   



________________________________
 From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Bob Clark
Sent: Tuesday, May 22, 2012 7:37 PM
To: re-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] Finding ground faults

  
Wrenches: 
  
Sorry to bring up this situation again, but I could not find a previous discussion thread that talked about step-by-step procedures for tracking down ground faults (I believe it was John Berdner who provided the bulk of the writing in that regard and it related to high voltage strings—not that 75-85 volts per string is all that low). 
  
We have an Outback FLEXpower Two system with 8, 3-module strings (Silicon Energy 190W, 25.3Vmp, 7.5 Imp) combined in a Midnite Solar MNPV12 combiner with breakers.  The cables from the array are routed to two different Wiley 4-string pass-through boxes (located under the two center strings) and then off of the roof and into the PV combiner. 
  
Up until this week the system has seen several weeks of awesome power production.  Yesterday, the rains came and the GFDI breaker tripped.  Every time it rains, the little green breaker on the GFDI trips off.  That tells me that the ground fault is occurring in a place where at least one of the conductors on one of the strings (possibly more) is getting wet and conducting current to ground. 
  
It would seem to me that the most likely place for moisture to cause a ground fault to occur in this system would be in the pass-through boxes.  This would mean removing the central modules to access the pass-through boxes. 
  
Any of you who have mounted the Silicon Energy modules know that the cables are contained in trays along the side of the modules until they are routed through conduit to the pass-through boxes.  So, if there is current going to ground from any of these cables, it could even be occurring in any of the 9 trays along side of the modules.  I do not like the idea of tracking down a ground fault in one of these trays as they are all interconnected. 
  
How best (and safely) to track down where the ground fault is occurring?  Any advice as to the best and safest way to track down the ground fault(s) would be greatly appreciated. 
  
Bob Clark 
SolarWind Energy Systems, LLC   
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