DC GFCI [RE-wrenches]

[Drake Chamberlin - Electrical Energy]

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At 11:48 PM 01/11/2002 +0000, you wrote:

>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).

The nail head could get hot.  If there is a fire danger from an array, it 
could manifest here.


>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.

Yes, I agree that the C-40 would probably act before the fuse.


>  Or the
>system might be batteryless.

Batteryless systems might be another issue.  I don't know.


>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


May be I'm not seeing it, but it seems to me that if the array negative 
became grounded, that ground would connect to the battery ground via the 
required grounding system.  The system negative connects to the ground rod, 
structural building metal and water piping.  To me it looks like a current 
path to ground would exist, completing the circuit.

Drake

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