Separately-derived means that there is physical isolation between two circuits
in the same electrical system – usually this involves two circuits connected by
a transformer
The DC side is separately derived in a transformer-based PV inverter. Most
grid-tie inverters have a DC main bonding jumper internally. Other inverters
(esp. small stand-alone inverters) may not, and so a main bonding jumper will
need to be installed.
Jeffrey Quackenbush
NABCEP-certified PV Installer
________________________________
From: Dave Palumbo <d...@independentpowerllc.com>
To: 'RE-wrenches' <re-wrenches@lists.re-wrenches.org>
Sent: Tuesday, January 24, 2012 6:43 AM
Subject: Re: [RE-wrenches] Grounding Separately Derived AC System
Regarding NEC Article 250.30 does Informational Note #1 mean that a standard
(no battery) grid-tied PV system is not a Separately Derived System?
I’m primarily interested on the consensus view of Bonding the Neutral (grounded
conductor) to Equipment Ground in a 60 Amp Fused Disconnect located between the
240VAC inverter output and AC point of connection on the load side of the meter
in the service disconnect enclosure in a supply side connected PV system.
250.30 Informational Note 1 reads: “An alternate ac power source, such as an
on-site generator, is not a separately derived system if the grounded conductor
is solidly interconnected to a service-supplied system grounded conductor…” I
believe a PV system meets that description as the Neutral stays connected at
all times.
My interpretation is that a standard net-metered PV system is therefore not a
separately derived system and the Neutral should not have a bonding jumper to
equipment ground in the Fused Disconnect.
Is this the correct interpretation?
David Palumbo
Independent Power LLC
462 Solar Way Drive
Hyde Park, VT 05655
www.independentpowerllc.com
NABCEP Certified PV Installer
Vermont Solar Partner
24 Years Experience, (802) 888-7194
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