Ground fault [RE-wrenches]

Bill Brooks billb at endecon.com
Mon Nov 18 21:20:37 PST 2002


William,

I think Allan's reply nailed it. There is no way that big of array could be
less than 30 amps. Check your Isc against irradiance on the array. I think
you will find a different story.

Bill.

-----Original Message-----
From: William Miller [mailto:wrmiller at slonet.org]
Sent: Friday, November 15, 2002 10:43 PM
To: RE-wrenches at topica.com
Subject: RE: Ground fault [RE-wrenches]


Bill:

I don't believe your assumptions are correct here.  The measured SC current
is no greater than 30 amps, conservative for the SB50.  Secondly, there was
indeed a wiring fault.  One of the positive leads running to the SB50 was
found to be pinched, the jacket pierced and the conductor touching the
metal framework with signs of heat.

William

At 03:58 PM 11/15/02 -0800, you wrote:
>Jeff,
>
>Installers, not fully understanding the designs they are
>working with feel like they can operate the equipment at, near, or slightly
>above the published rating think that "there must be a safety margin in
>here."
>
>All these bad assumptions result in smoke. My guess is that the unit was
>overpowered in the fall of the year when the sun was hitting the modules
>straight on, voltage was higher because of the cooler weather, and the
>controller ran out of current/temperature headroom and something gave up.
>
>The ground fault is likely the result of the board insulation disappearing.
>All speculation, but don't fault the wiring until you find the bad wire.
>Equipment fails more often unless the installer is careless.
>
>By the way, intermittent insulation faults are extremely common with
damaged
>wiring. The initial voltage check certainly is an absolute must, but an
>insulation test taking all your wiring to 500V is a much better test. This
>is commonly done in large commercial industrial projects but is rarely done
>on small commercial and residential electrical projects (doesn't make it
any
>less important however). Even this test does not solve all problems. That
is
>why GFPs are so valuable. They will catch that intermittent fault when
these
>other methods fail.
>
>Bill.
>
>
>
>
>
>-----Original Message-----
>From: Jeffery Wolfe, Global Resource Options
>[mailto:jeff at globalresourceoptions.com]
>Sent: Friday, November 15, 2002 3:33 PM
>To: RE-wrenches at topica.com
>Subject: RE: Ground fault [RE-wrenches]
>
>
>>From what I've heard, most of these problems, including the one we've been
>discussing, happen at install. I think a voltage check would have caught
>this one.
>
>Jeff
>
>-----Original Message-----
>From: Bill Brooks [mailto:billb at endecon.com]
>Sent: Friday, November 15, 2002 2:10 PM
>To: RE-wrenches at topica.com
>Subject: RE: Ground fault [RE-wrenches]
>
>
>
>Jeff,
>
>A Voc test on your wiring is only going to find gross wiring mistakes. A
GFP
>works 24-7 to find those faults that don't show up until later.
>
>Bill.
>
>-----Original Message-----
>From: Jeffery Wolfe, Global Resource Options
>[mailto:jeff at globalresourceoptions.com]
>Sent: Thursday, November 14, 2002 5:38 PM
>To: RE-wrenches at topica.com
>Subject: RE: Ground fault [RE-wrenches]
>
>
>I'm not ready to add PVGFP's to all my installs. I think that's overkill,
>and not addressing the problem of adequate installation (by whoever
installs
>the panels).
>***snip***
>
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William Miller
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