DC GFCI [RE-wrenches]

[Bill Brooks]

Travis,

On a line-to-ground fault, the grounding path is removed and therefore the
return path for the fault current is broken. Again, it doesn't solve all
faults, just those that are more likely to happen. Historically, ground
faults have been the source of failures of older arrays and various wiring
mistakes.

If you bolt the positive and negative together (e.g. with a metal staple
through both--good reason never to use metal staples), the GFP may not
detect this fault, but the inverter likely will because most inverters
detect array shorts. If it is a battery-based system, the reverse current
from the battery will normally trip the main breaker.

Can you think of a fault that isn't covered? I'm sure there are some high
impedance line-to-line faults that might go undetected, but they will likely
deteriorate into one of these other faults and cause a trip. All-in-all, the
GFP fills a major gap in detection of faults that normal overcurrent
protection is likely to miss.

Bill.



-----Original Message-----
From: Travis Creswell, Ozark Solar [mailto:ozsolar at ipa.net]
Sent: Friday, January 11, 2002 12:33 PM
To: RE-wrenches at topica.com
Subject: Re: DC GFCI [RE-wrenches]


I never did understand what it's protecting.  I don't remember anything
about a Canadian lab questioning them.  That does sound an awful lot like
what I posted, though.

The main problem I saw, and still do see with them was as such;

A fault happens somewhere in between the inverter and the roof mounted
panels.  The GFP detects this fault and opens the circuit.   Since the
panels are still producing power the fault is still merrily smoldering away
on the roof or in the attic until sunset.  Hopefully the customer notices
the breaker is tripped before the house catches fire.

Wow, now that's helpful a device.

Travis Creswell
Ozark Energy Services, Inc.
----------
>From: Drake Chamberlin - Electrical Energy <solar at eagle-access.net>
>To: RE-wrenches at topica.com
>Subject: DC GFCI [RE-wrenches]
>Date: Fri, Jan 11, 2002, 1:08 PM
>

>Long ago, someone on the list mentioned that personnel in a Canadian Lab
>felt that the DC GFCI, mounted near the batteries, for roof mounted systems
>wasn't an effective safety device.
>
>Does anyone remember the reference on that?
>
>Thanks,
>
>Drake
>
>

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