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

[August Goers]

Hi Mac,



I think the answer to your "separately derived system" question is in the
code snippet you pasted in below. Clearly, your Enphase grid tied system
has a direct electrical connection to the utility. A generator system that
runs while the grid is down would be an example of a separately derived
system since it will always have a transfer switch to separate the
electrical connections. In other words, the grid tied solar system is
designed to work in unison with the grid while a separately must only
operate independently. At least that is how I try to explain it to
inspectors around here.



I believe Brian Mehalic's email clearly speaks to why you still need a GEC
for the Enphase based system. Incidentally, we're starting to work with
listed ACPV modules and transformerless (non-isolated) inverters which
don't have a DC GEC requirement. This is a major benefit to help reduce
installed costs.



Best,



August





August Goers



Luminalt Energy Corporation

1320 Potrero Avenue

San Francisco, CA 94110

m: 415.559.1525

o: 415.641.4000

august at luminalt.com



*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *mac Lewis
*Sent:* Wednesday, November 28, 2012 7:56 PM
*To:* RE-wrenches
*Subject:* [RE-wrenches] EGC vs GEC, separately derived system



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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