[RE-wrenches] EGC vs GEC, separately derived system

[Brian Mehalic]

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 <maclewis1 at 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
> *
>
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