[RE-wrenches] ground fault troubleshooting

[Tom DeBates]

hello Wrenches,
  We recently had an interesting (amusing?) experience that I thought might be worth sharing and to get some feedback.
  I received a call from a fellow contractor that had a ground fault in his PV system (Wattsun DA tracker, 24 Siemens (Shell?)110, 1 string, Sunny Boy 2500). The GF fuse in the Sunny Boy had blown. Another installer and I went to his site to try to determine what the cause was. fortunately the Ground Fault article by Paul Mync had just been in Solar Pro and we used this as a template for troubleshooting the problem. To make a long story short, we spent the better part of a day troubleshooting and still could not solve the problem. What seemed to be happening was that we were getting a different ground fault current based upon how many modules we had eliminated for the string and it seemed to be approximately proportional. 
  A few days later our friend was going to run through the procdedure again and take better notes. Since I was not there, the details may be a bit sketchy, but basically are as follows. As he reconnected the positive(ungrounded) home-run at the module j-box, the lightning arrestor (Delta LA602DC), proceeded to "go off like a Roman candle". As he pulled the conductor off the terminal he got a nice arc between them. The obvious thing to do was to eliminate the arrestor.... that solved the problem. Upon further inspection, the arrestor had a crack in the case. Had the arrestor had a slight fault (due to moisture) initially that lead to leakage current based upon voltage applied and then finally "fully-faulted"?
  At least two lessons here:
1. When troubleshooting a GF, always eliminate any accessories from the system.
2. When dealing with a faulted array never assume that opening the grounded conductor will open the circuit. Just wondering...would a jumper form grounded conductor to ground had prevented the acring he experienced?
thanks,
tom

Tom DeBates

Habi-Tek

524 Summit St.

Geneva,IL. 60134

    630-262-8193

fax 630-262-1343


      
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