[RE-wrenches] Grounding Separately Derived AC System

[JRQ]

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 <dave at independentpowerllc.com>
To: 'RE-wrenches' <re-wrenches at 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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