[RE-wrenches] DC Bonding battery systems

[William Miller]

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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