<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div><span>If neutrals are connected together on either side of a transformer, then there no longer is complete physical isolation. The ungrounded conductors would be isolated, but not the grounded conductors.</span></div><div><span><br></span></div><div><span>My interpretations is that there wouldn't have to be loads on either side for a system to be separately derived – there just has to be a current-carrying circuit on either side.</span></div><div><span><br></span></div><div><span>Yes. 690 is very clear about bonding between the DC and AC sides of an inverter, independent of what is in 250 (and I'm glad they've clarified the language on this in recent editions).</span></div><div><br></div><div>Jeffrey Quackenbush</div><div>NABCEP-certified PV Installer</div><div><div><div class="yui_3_2_0_33_132747457788569"
style="font-family: 'times new roman', 'new york', times, serif; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-size: 12pt; "><div>Peripatetic Solar Technician</div></div></div></div><div><br></div> <div style="font-size: 12pt; font-family: 'times new roman', 'new york', times, serif; "> <div style="font-size: 12pt; font-family: 'times new roman', 'new york', times, serif; "> <div dir="ltr"> <font size="2" face="Arial"> <hr size="1"> <b><span style="font-weight:bold;">From:</span></b> Ray Walters <ray@solarray.com><br> <b><span style="font-weight: bold;">To:</span></b> RE-wrenches <re-wrenches@lists.re-wrenches.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Wednesday, January 25, 2012 12:20 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: [RE-wrenches] Grounding Separately Derived AC System<br> </font> </div> <br>
<div id="yiv2087226859">
<div>
I can see the confusion over this. We've had this discussion for
almost a decade, and its been made more clear by improved language
and by interpretation by folks like John Wiles and Bill Brooks. The
definition of separately derived system is just not quite clear
enough still. Despite this confusion however, 250.30 which Dave
referenced in his original question is titled:<br>
" Grounding Separately Derived <u>Alternating Current</u>
Systems", so it doesn't apply to DC at all. (whether or not we
consider the DC side to be separately derived) So just to re-answer
Dave's original question: 250.30 does Not apply to grid tied PV.<br>
<br>
After rereading several parts of the code, I can totally see
Jeffrey's interpretation of the DC side being isolated by the
inverter's transformer (and therefore separately derived). However,
I was taught that a separately derived system has not only its own
isolated source, but it feeds it's own isolated loads (its a
complete premises wiring system). As soon as neutrals are connected
together, it's not separately derived. They need to clear up this
question with some language in 690, 705, or in 100, the definition
of separately derived system. <br>
In the end, I don't believe it matters whether we consider the DC
side to be separately derived or not, as 250.30 only applies to AC,
and 690 is now fairly clear about bonding and grounding requirements
regardless. <br>
<br>
Ray Walters<br>
<br>
On 1/24/2012 9:10 PM, JRQ wrote:
<blockquote type="cite">
<div style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-size: 12pt; font-family: 'times new roman', 'new york', times, serif; ">
<div><span>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</span></div>
<div><span><br>
</span></div>
<div><span>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.</span></div>
<div><span><br>
</span></div>
<div><span>Jeffrey Quackenbush</span></div>
<div>NABCEP-certified PV Installer</div>
<div><br>
</div>
<div style="font-size: 12pt; font-family: times, serif; ">
<div style="font-size: 12pt; font-family: times, serif; ">
<div dir="ltr"> <font face="Arial" size="2">
<hr size="1"> <b><span style="font-weight:bold;">From:</span></b>
Dave Palumbo <a rel="nofollow" class="yiv2087226859moz-txt-link-rfc2396E" ymailto="mailto:dave@independentpowerllc.com" target="_blank" href="mailto:dave@independentpowerllc.com"><dave@independentpowerllc.com></a><br>
<b><span style="font-weight:bold;">To:</span></b>
'RE-wrenches' <a rel="nofollow" class="yiv2087226859moz-txt-link-rfc2396E" ymailto="mailto:re-wrenches@lists.re-wrenches.org" target="_blank" href="mailto:re-wrenches@lists.re-wrenches.org"><re-wrenches@lists.re-wrenches.org></a>
<br>
<b><span style="font-weight:bold;">Sent:</span></b>
Tuesday, January 24, 2012 6:43 AM<br>
<b><span style="font-weight:bold;">Subject:</span></b>
Re: [RE-wrenches] Grounding Separately Derived AC System<br>
</font> </div>
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<div class="yiv2087226859WordSection1">
<div class="yiv2087226859MsoNormal">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?</div>
<div class="yiv2087226859MsoNormal"> </div>
<div class="yiv2087226859MsoNormal">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 <u>supply side connected PV system</u>.
</div>
<div class="yiv2087226859MsoNormal"> </div>
<div class="yiv2087226859MsoNormal">250.30
Informational Note 1 reads: “<i>An alternate ac
power source, such as an on-site generator, is <u>not</u>
a separately derived system if the grounded
conductor is solidly interconnected to a
service-supplied system grounded conductor…” </i> I
believe a PV system meets that description as the
Neutral stays connected at all times. </div>
<div class="yiv2087226859MsoNormal"><i> </i></div>
<div class="yiv2087226859MsoNormal">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.</div>
<div class="yiv2087226859MsoNormal"> </div>
<div class="yiv2087226859MsoNormal">Is this the correct
interpretation?</div>
<div class="yiv2087226859MsoNormal"> </div>
<div class="yiv2087226859MsoNormal">David Palumbo</div>
<div class="yiv2087226859MsoNormal">Independent Power
LLC </div>
<div class="yiv2087226859MsoNormal">462 Solar Way Drive</div>
<div class="yiv2087226859MsoNormal">Hyde Park, VT 05655</div>
<div class="yiv2087226859MsoNormal"><b><i><a rel="nofollow" target="_blank" href="http://www.independentpowerllc.com">www.independentpowerllc.com</a>
</i></b></div>
<div class="yiv2087226859MsoNormal">NABCEP Certified PV
Installer</div>
<div class="yiv2087226859MsoNormal">Vermont Solar
Partner</div>
<div class="yiv2087226859MsoNormal">24 Years
Experience, (802) 888-7194 </div>
<div class="yiv2087226859MsoNormal"> </div>
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