Ground fault [RE-wrenches]

[William Miller]

Colleagues:

Over the last weekend I received a call from a client reporting that an RV
products SB50 that I installed for him had "burned up."   I went out first
thing Monday to look at it and almost pooped my pants. The unit had burnt
inside to a crisp and damn near sent his warehouse up in flames.  This was
some serious fire and it scared me.

We have performed some analysis on what caused the problem and posted a
pretty comprehensive report on our web site (url in my signature lines
below.  Click on Case Studies.  The photos and diagrams are somewhat large
to show adequate detail, so download this when you have the time).

Part of the problem may be that the client keeps adding legacy Cariso PV
modules.  He wants to increase his charging and may well have exceeded the
capability of the SB50.  One reason he adds modules is that he may not be
getting a realistic charge rate because the ground fault we discovered may
have been siphoning off amps for some time.  The problem may existed for
some time and came to a head when we finally received rain here after a
long dry summer.  The ground conductivity may have increased enough to
bring this problem to a critical point.

The only reason the fire did not spread is that the client put a sheet
metal cover over the equipment to prevent water damage in the case of a
roof leak.

I believe there are two lessons to be learned:  Ground fault breakers may
be more valuable than I could have imagined, and sheet metal backing is a
valuable addition to any installation.  These are both ideas discussed
here, and they may warrant further discussion.

I was off the hook on this installation because the client wired his own
arrays.  Having said this, it would be very easy for anyone to create this
kind of fault.  Using tray cable, for example, one could easily pinch a
positive wire in a rack foot when lowering a rack.  All of this scares me
and makes me want to perform all of my installs like delicate surgery.

Comments are appreciated. I especially want to hear if anyone agrees or
disagrees with the premise that a GFI would have prevented the failure.  If
so, the point is not to require a GFI when the arrays are on the roof of a
dwelling, but when any of the circuitry is IN or runs through the dwelling.

Thanks for reviewing this case and commenting.

William Miller

__________________________________________________________________
William Miller
Miller Power and Communications
PO Box 50, Santa Margarita, CA 93453
Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
email: wrmiller at slonet.org
http://millerpowerandcomm.com
License No. C-10-773985
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