<div dir="ltr"><div class="gmail_default" style="font-family:verdana,sans-serif">I thought one of the the rationale for the upsized conductor between panelboards in series was to account for the possibility that the conductor could be later tapped with other loads or backfed from another PV source in theory. I never thought that rationale was reasonable - any future changes of this significance would need to be addressed at that time anyway.</div>
<div class="gmail_default" style="font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif">I have found that AHJs are lenient and reasonable on this point if addressed in advance. It should only be an issue in NEC 2008 and 2011 if using a load side connection. If your jurisdiction allows it, a supply side connection should bypass this issue altogether. When using a subpanel to combine multiple inverter outputs, it's often the case that a load side connection is not possible in retrofit situations, at least in my experience. Even on a 1600A commercial main bus where the 120% rule is a non-factor, there are often prohibitive issues that make a supply-side connection much more cost effective. For example, I've run into manual generator switches or situations where it is impractical to move breakers to accommodate the proper backfed breaker location. </div>
<div class="gmail_default" style="font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif">By the way, we've had this discussion before. Search the archives for:</div>
<div class="gmail_default"><font face="verdana, sans-serif">"sizing a sub-panel used to combinemultipleinverter outputs"</font><br></div><div><br></div><div><div class="gmail_default" style="font-family:verdana,sans-serif">
(there are several prior discussions on the subject)</div><br></div><br><div id="WISESTAMP_SIG_gmail_session"><div style="font-size:13px;font-family:Verdana,Arial,Helvetica,sans-serif"><div style="margin:0px 0px 8px"><p style="margin:0px">
<span><span>Jason Szumlanski</span></span></p><p style="margin:0px"></p><div class="gmail_default" style="font-family:verdana,sans-serif;display:inline">Fafco Solar</div><br> </div></div></div><div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Mar 5, 2014 at 10:30 AM, Dave Click <span dir="ltr"><<a href="mailto:daveclick@fsec.ucf.edu" target="_blank">daveclick@fsec.ucf.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
I think there's plenty of room to interpret the 2008 and 2011 NEC
such that you don't need to upsize this conductor either. 2008
690.64(B)(2) and 2011 705.12(D)(2) are both titled "bus or
conductor," and as Brian points out below the currents aren't
additive. As I understand it the 120% rule was because panelboard
manufacturers weren't comfortable with exceeding 120% due to heat
concerns under continuous operation (assuming a fully loaded
panelboard). As for conductors, I wonder if that 120% was just to
keep it consistent with the panelboard requirement, even though it
would be safe at levels >120% as long as you're feeding from
opposite ends.<br>
<br>
Also, since you seem to be talking about a good amount of PV with
your 2 SolarEdge 20s, make sure your upstream breakers are OK to be
backfed (up through and including the main, unless you've got a
large, guaranteed baseload).<br>
<br>
DKC <br><div><div class="h5">
<br>
<div>On 2014/3/5, 10:01, Brian Mehalic
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">A very clarifying change is what I'd call it!
<div><br>
</div>
<div>First off, rather than being based on the actual breaker
size on the inverter output circuit, calcs are instead based
on 125% of the inverter rated output current.<br>
<div><br>
</div>
<div>705.12(D)(2)(1) addresses "Feeders" - but only applies
when the inverter output circuit connection is made
somewhere other than the opposite end of the feeder from the
utility supply. This addresses concerns about whether the
feeder conductor needs to be larger due to the presence of
the additional source of supply, and so long as the inverter
isn't connected to the feeder in the middle of it then the
existing conductor size should be okay (because if it is at
the opposite end of the feeder than there is nowhere where
the utility and inverter current will be additive).</div>
</div>
<div><br>
</div>
<div>705.12(D)(2)(3) addresses "Busbars" and allows several
options, including the familiar "120% rule" as you stated in
your original post. Also check out 705.12(D)(2)(3)(c) -
depending on the load breakers in the subpanel, the 120% rule
may not even need to be used (if the sum of the inverter and
load breakers is less than or equal to the busbar rating).</div>
<div><br>
</div>
<div>And remember, even if your AHJ hasn't adopted 2014 yet it
is worth having a conversation with them to see if they'll
allow you to design the system based on the new Code - after
all, in a certain sense, the 2014 NEC is what "they" meant the
2011 NEC to say!</div>
<div><br>
</div>
<div>Cheers,</div>
</div>
<div class="gmail_extra"><br clear="all">
<div>
<div dir="ltr">
<div><br>
</div>
<div>Brian Mehalic <br>
NABCEP Certified Solar PV Installation
Professional™ R031508-59
<div>IREC ISPQ Certified Affiliated Instructor/PV US-0132<br>
<div><br>
</div>
<div>PV Curriculum Developer and Instructor
<div>Solar Energy International<br>
<a href="http://www.solarenergy.org" target="_blank">http://www.solarenergy.org</a></div>
</div>
</div>
</div>
</div>
</div>
<br>
<br>
<div class="gmail_quote">On Tue, Mar 4, 2014 at 5:21 PM, Kirk <span dir="ltr"><<a href="mailto:kirk@vtsolar.com" target="_blank">kirk@vtsolar.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div dir="auto">
<div>Is this a code change in 2014 vs 2011 or merely a
clarification? Vt has not adopted 2014 yet. What was the
original rationale for the 120% rule to apply to
conductors in addition to a panel bus? <span><font color="#888888"><br>
<br>
Kirk Herander
<div>VSE</div>
</font></span></div>
<div>
<div>
<div><br>
On Mar 4, 2014, at 6:20 PM, Brian Mehalic <<a href="mailto:brian@solarenergy.org" target="_blank">brian@solarenergy.org</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
<div>If the subpanel is at the end if the feeder,
and there are no taps in between the main and
the sub then I don't see any reason that the
conductors need to be any larger than 200 A as
there is no where on the feeder conductors where
grid and PV current will be additive. </div>
<div><br>
</div>
<div>The changes in 705.12 in 2014 address this in
large part. <br>
<br>
Brian</div>
<div><br>
On Mar 4, 2014, at 2:41 PM, "Kirk Herander" <<a href="mailto:kirk@vtsolar.com" target="_blank">kirk@vtsolar.com</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Solaredge
20 kw, 480 3-phase. Good point, but that
may be irrelevant. The feed-in subpanel
is also powering unrelated loads, which
use the neutral as a conductor from the
main panel. So 4 conductors from the
main.</span></p>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></p>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Kirk
Herander</span></p>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">VT
Solar, LLC</span></p>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">dba
Vermont Solar Engineering</span></p>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">NABCEP<sup>TM
</sup>Certified Inaugural Certificant</span></p>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">NYSERDA-eligible
Installer</span></p>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">VT
RE Incentive Program Partner</span></p>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><a href="tel:802.863.1202" value="+18028631202" target="_blank">802.863.1202</a></span></p>
</div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></p>
<div>
<div style="border-style:solid none none;border-top-color:rgb(181,196,223);border-top-width:1pt;padding:3pt 0in 0in">
<p class="MsoNormal"><b><span style="font-size:10pt;font-family:Tahoma,sans-serif">From:</span></b><span style="font-size:10pt;font-family:Tahoma,sans-serif">
<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b>Allen Frishman<br>
<b>Sent:</b> Tuesday, March 04, 2014
4:32 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches]
conductors and the 120% rule</span></p>
</div>
</div>
<p class="MsoNormal"> </p>
<p class="MsoNormal">
what inverter(s) are you using? In many
cases the Neutral is not considered a
Current Carying Conductor by the
Manufacturer and therefore you only have 3
CCC.</p>
<div>
<div>
<p class="MsoNormal"><i><span style="font-size:10.5pt">Al
Frishman</span></i><span style="font-size:13.5pt"><br>
</span><span style="font-size:13.5pt;color:rgb(3,1,0)">Aeon</span><span style="font-size:13.5pt;color:rgb(255,151,0)">Solar</span><span></span></p>
<p class="MsoNormal"><i><span style="font-size:10.5pt"><a href="tel:%28917%29%20699-6641" target="_blank">(917) 699-6641</a> -
cell</span></i><span style="font-size:10.5pt"><br>
<i><a href="tel:%28888%29%20460-2867" target="_blank">(888) 460-2867</a></i><br>
<i><a href="http://www.aeonsolar.com/" target="_blank">www.aeonsolar.com</a></i></span><span></span></p>
</div>
</div>
<p class="MsoNormal">
</p>
<div>
<div>
<p class="MsoNormal">On Mar 4, 2014, at
4:20 PM, Kirk Herander wrote:</p>
</div>
<p class="MsoNormal"><br>
<br>
</p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Approx..
50 – 60ft.</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span><span></span></p>
</div>
<div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Kirk
Herander</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">VT
Solar, LLC</span><span></span></p>
</div>
<div>
<p class="MsoNormal">
<span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">dba
Vermont Solar Engineering</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">NABCEP<sup>TM<span> </span></sup>Certified
Inaugural Certificant</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">NYSERDA-eligible
Installer</span><span></span></p>
</div>
<div>
<p class="MsoNormal">
<span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">VT
RE Incentive Program Partner</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><a href="tel:802.863.1202" value="+18028631202" target="_blank">802.863.1202</a></span><span></span></p>
</div>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span><span></span></p>
</div>
<div>
<div style="border-style:solid none none;padding:3pt 0in 0in">
<div>
<p class="MsoNormal"><b><span style="font-size:10pt;font-family:Tahoma,sans-serif">From:</span></b><span><span style="font-size:10pt;font-family:Tahoma,sans-serif"> </span></span><span style="font-size:10pt;font-family:Tahoma,sans-serif"><a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a><span> </span><a href="mailto:[mailto:re-wrenches-bounces@lists.re-wrenches.org]" target="_blank">[mailto:re-wrenches-bounces@lists.re-wrenches.org]</a><span> </span><b>On
Behalf Of<span> </span></b>Ray
Walters<br>
<b>Sent:</b><span> </span>Tuesday,
March 04, 2014 4:05 PM<br>
<b>To:</b><span> </span>RE-wrenches<br>
<b>Subject:</b><span> </span>Re:
[RE-wrenches] conductors and
the 120% rule</span><span></span></p>
</div>
</div>
</div>
<div>
<p class="MsoNormal"><span> </span></p>
</div>
<div>
<div>
<p class="MsoNormal"><span>What
is the length of the conduit to
the subpanel? That will
determine whether to apply the
derates.<br>
<br>
<br>
</span></p>
</div>
<pre><span>R.Ray Walters</span></pre>
<pre><span>CTO, Solarray, Inc</span></pre>
<pre><span>Nabcep Certified PV Installer, </span></pre>
<pre><span>Licensed Master Electrician</span></pre>
<pre><span>Solar Design Engineer</span></pre>
<pre><span><a href="tel:303%20505-8760" value="+13035058760" target="_blank">303 505-8760</a></span></pre>
<div>
<p class="MsoNormal"><span>On
3/4/2014 1:34 PM, Kirk Herander
wrote:</span></p>
</div>
</div>
<blockquote style="margin-top:5pt;margin-bottom:5pt">
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Whether
or not a further derate has to
be applied is the killer here,
as I am working with existing
panels and conductors. In an old
Code Corner(HP140) J. Wiles goes
through a similar scenario and
calls out the allowable current
rating and conductor in 310.15,
but makes no mention of applying
additional derate factors. The
.8 derate for 4-6
conductors(l1,l2,l3, & n)
will put the existing 4/0 cable
between feed-in and main panel
at 208 amps, less than the
allowable 217. I’d hate to need
to upsize the wire to 250 mcm.</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Kirk
Herander</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">VT
Solar, LLC</span><span></span></p>
</div>
<div>
<p class="MsoNormal">
<span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">dba
Vermont Solar Engineering</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">NABCEP<sup>TM<span> </span></sup>Certified
Inaugural Certificant</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">NYSERDA-eligible
Installer</span><span></span></p>
</div>
<div>
<p class="MsoNormal">
<span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">VT
RE Incentive Program Partner</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><a href="tel:802.863.1202" value="+18028631202" target="_blank">802.863.1202</a></span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span><span></span></p>
</div>
<div>
<p class="MsoNormal"><b><span style="font-size:10pt;font-family:Tahoma,sans-serif">From:</span></b><span><span style="font-size:10pt;font-family:Tahoma,sans-serif"> </span></span><span style="font-size:10pt;font-family:Tahoma,sans-serif"><a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a><span> </span>[<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]<span> </span><b>On
Behalf Of<span> </span></b>Jason
Szumlanski<br>
<b>Sent:</b><span> </span>Tuesday,
March 04, 2014 2:57 PM<br>
<b>To:</b><span> </span>RE-wrenches<br>
<b>Subject:</b><span> </span>Re:
[RE-wrenches] conductors and the
120% rule</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span> </span></p>
</div>
<div>
<div>
<div>
<p class="MsoNormal"><span style="font-family:Verdana,sans-serif">Both
the bus and conductors need
to be rated for 217 amps
minimum. As you mentioned,
the bus is not a problem.
The way I interpret it, the
conductor size required
would be after derate
factors are applied. The
rating of the conductor is
ultimately dependent on the
derate factors.</span><span></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><span style="font-family:Verdana,sans-serif"> </span><span></span></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><span style="font-family:Verdana,sans-serif">If
you can locate your subpanel
adjacent to the main
distribution panel, you may
be able to use Exception #3
to 310.15(B)(2) by
connecting the panels with a
short nipple. I assume you
are just looking at a number
of conductor derate and not
an ambient temperature
derate.</span><span></span></p>
</div>
</div>
<div>
<p class="MsoNormal"><span> </span></p>
</div>
<div>
<div>
<div style="margin-bottom:6pt">
<div>
<p class="MsoNormal"><span style="font-size:10pt;font-family:Verdana,sans-serif">Jason
Szumlanski</span><span></span></p>
</div>
<div>
<div>
<p class="MsoNormal"><span style="font-size:10pt;font-family:Verdana,sans-serif">Fafco
Solar</span><span></span></p>
</div>
</div>
<div>
<p class="MsoNormal"><span style="font-size:10pt;font-family:Verdana,sans-serif"><br> </span></p></div></div>
</div>
</div>
<div>
<p class="MsoNormal" style="margin-bottom:12pt"><span> </span></p>
<div>
<div>
<p class="MsoNormal"><span>On Tue, Mar 4,
2014 at 12:05 PM, Kirk
Herander <<a href="mailto:kirk@vtsolar.com" target="_blank">kirk@vtsolar.com</a>>
wrote:</span></p>
</div>
<div>
<div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">Hello,</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">I have a 225 amp 3-phase main lug sub-panel
protected by a 200 amp
breaker. My inverter
breaker feeding the
sub panel is 60 amps.
So 225 a bus x 1.2 =
270 amps. That’s less
than the sum of the
two breakers of 260
amps, so no issue
there. The conductors
between sub and main
panel have to be rated
for at least 260/1.2 =
217 amps, correct? Is
this 217 amps before
or after derating the
conductor?</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt"> </span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt"> </span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">Kirk Herander</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">VT Solar, LLC</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">dba Vermont Solar Engineering</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">NABCEP<sup>TM<span> </span></sup>Certified
Inaugural Certificant</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">NYSERDA-eligible Installer</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt">VT RE Incentive Program Partner</span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:14pt"><a href="tel:802.863.1202" target="_blank">802.863.1202</a></span><span></span></p>
</div>
<div>
<p class="MsoNormal"><span> </span></p>
</div>
</div>
</div>
</div>
<div>
<p class="MsoNormal"><span> </span></p>
</div>
</div>
</div>
<div>
<p class="MsoNormal"><span><br></span></p></div></blockquote></div></div></div></div></blockquote></div></blockquote></div></div></div></blockquote></div></div></blockquote></div></div>
</div><br></blockquote></div><br></div></div>