[RE-wrenches] DC Bonding battery systems

[Darryl Thayer]

Hi Bill, I have thought about it also.  The ground fault detection
interruption system does elevate one of the conductors to voltage.  This
makes it hazardous.  However, it also protects from a PV hot to ground arc
fault.  There are three types of arc faults in PV systems, the ground fault
arc, the series arc fault, and the parallel arc fault.  It is the parallel
arc that was addressed in the 2017 NEC via module-level shutdown.  The
intent of 690.11 can not be addressed without 2017 690.12.b(2) where the
detection of an arc must shutdown the array currents.

On Mon, Jul 22, 2019 at 3:42 PM William Miller <william at millersolar.com>
wrote:

> Wrenches:
>
>
>
> Here is a question that has bothered me for some time:  If one is using a
> GFD (ground fault detection) breaker on a PV feeder(s) to a battery
> inverter system, the state of the industry is to use a breaker with an
> extra 0.5 or 1 amp pole.  This section of the breaker connects, or bonds
> the DC negative, or grounded conductor, to the grounding system.
>
>
>
> In order for the GFD breaker to work one needs to isolate the grounded bus
> bar (negative).  If there is a ground fault the breaker opens and breaks
> the bond.
>
>
>
> This goes very much against my conceptualization of how a bonding system
> should work.  The bond should never be broken, particularly when there is a
> fault in the system.  When this breaker opens, either manually or by an
> overcurrent condition on any pole, the DC bond is removed for all portions
> of the DC system.
>
>
>
> There is a prominent personality in the industry that often presents
> academic opinions on solar related electrical issues in articles and in
> seminars.  This person claimed to have invented this GFD system, but when
> pressed to comment on the concerns mentioned above, changed the subject.
>
>
>
> I believe ground fault protection is important.  I just don’t believe the
> method the industry has offered is really effective in solving the issues
> presented in a ground fault scenario.
>
>
>
> I believe similar issues present on non-battery PV systems with the simple
> fuse in the ground system found on many inverters.  I know some
> troubleshooting guides warn of energized parts in ground fault conditions.
>
>
>
> Have any of you thought about these concerns?  Are my concerns valid?
> What are your policies on this subject?
>
>
>
> Thanks in advance for any insight.
>
>
>
> William Miller
>
>
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com
>
> CA Lic. 773985
>
>
>
> Quote of the month:  “As they age, batteries transition from energy
>
> storage devices to energy consuming devices.“ W. Miller
>
>
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