[RE-wrenches] ground fault troubleshooting

[Bill Brooks]

Tom,

 

Your dc clamp-on meter would have saved you from removing a conductor that
had current on it. It is likely a lightning event caused the LA602 to do its
job-thus the cracked case. The dc clamp-on meter would have shown the
current flowing into the SOV and on to ground.

 

Bill.

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Tom DeBates
Sent: Monday, April 05, 2010 7:04 PM
To: re-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] ground fault troubleshooting

 


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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