The separately derived issue aside, enphase inverters have an internal DC system ground and a marked point from which a DC GEC must be installed. Typically grounding is being done in the manner stated in 690.47(C)(3) - a single conductor as both the DC GEC and EGC, meaning it has to be the larger of the two sizes required; for most enphase systems, based on the interconnection breaker size, the minimum EGC would typically be #12 (Table 250.122), but the minimum size for a DC EGC is #8. A #6 may be preferable under the array due to interpretations about the conductor being subject to damage.
Brian Mehalic NABCEP Certified Solar PV Installer™ R031508-59 IREC ISPQ Certified Affiliated Instructor/PV US-0132 PV Curriculum Developer and Instructor Solar Energy International http://www.solarenergy.org On Wed, Nov 28, 2012 at 10:56 PM, mac Lewis <maclew...@gmail.com> wrote: > Hello wrenches, > > What constitutes a separately derived system? Would you consider a > breaker tied enphase system a separately-derived system? Suddenly, > inspectors in our AHJ are considering all PV systems separately derived > systems and thus requiring applying GEC sizing (as opposed to EGC sizing) > from the inverter(s) to the tie in point. This does not jive with my > understanding. Would like to hear other thoughts about this. > > Here is the definition of a separately derived system as per 2008 NEC > Article 100 Definitions: > > *Separately Derived System*: *A premises wiring system whose power is > derived from a source of electric energy or equipment other than a service. > Such systems have no direct electrical connection, including a solidly > connected grounded circuit conductor, to supply conductors originating in > another system.* > > For your enphase systems do you size your ground from roof to the breaker > panel as an EGC or a GEC? > > > Thanks in advance for your thoughts. > > -- > > > > Mac Lewis > > * > > "Yo solo sé que no sé nada." -Sócrates > * > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > >
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