DC GFCI [RE-wrenches]

Christopher Freitas - OutBack Power cfreitas at outbackpower.com
Fri Jan 11 15:48:20 PST 2002


Drake Chamberlin - Electrical Energy wrote:
> The ground fault detector is near the batteries not the array.  In the 
> event of a nail through a cable, shorting positive to ground, wouldn't 
> the circuit from the array continue to short even if the device were 
> tripped?

If the "nail through the cable connected postive to negative - yes 
current would still flow from the PV array and no hazard would be 
present (except for the nail itself).  There would not be a "ground 
fault" in essence.  The breaker on the battery may or may not trip (C40 
controllers have very fast electronic protection - faster than breakers) 
or the impedance of the cabling may also limit fault  currents.  Or the 
system might be batteryless.  

If the nail connected the positive or negative conductor to the 
grounding system then the DC-GFP would trip and the PV array would be 
disconnected from the rest of the system.  The DC bond from the negative 
to ground would be switched from low impedance (less than an ohm) to 
high impedance (50,000 ohms) to limit the current flowing in the fault 
and the grounding system.  

It is hard to imagine all of this in ones head - you need to draw it out 
to really see.  Kinda hard to do on a list...  

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas at outbackpower.com  www.outbackpower.com
Tel 360 435 6030  Arlington WA USA

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