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Daryl:<br><br>
I apologize for my ignorance, but I can't seem to find this exception in
the 2008 code. Can you cite the section?<br><br>
Unless you can physically prevent the addition of a load breaker in your
AC combiner panel, 690.64 does not apply. Any panel is capable of
supplying branch circuits. I think this disqualifies 690.64, so I
am looking for the section that allows a PV only panel.<br><br>
Thanks,<br><br>
William<br><br>
<br><br>
<br><br>
<br>
At 06:44 PM 6/26/2012, you wrote:<br>
<blockquote type=cite class=cite cite>I have found inspectors agree that
if it is labled "Solar only no Load circuits" the main breaker
protects this panel, or the sum of the breakers does not exceed the
busbar rating, the panel is protected without using the 120% rule<br>
I agree with Kirk <br><br>
<font size=2><b>From:</b> Kirk Herander <kirk@vtsolar.com><br>
<b>To:</b> 'RE-wrenches' <re-wrenches@lists.re-wrenches.org> <br>
<b>Sent:</b> Tuesday, June 26, 2012 3:53 PM<br>
<b>Subject:</b> [RE-wrenches] combiners and the 120% rule<br>
</font><br>
Jason,<br>
<br>
In your email below you state:<br>
<br>
\u201cYou DO need to observe the 120% rule for the combining subpanel,
regardless of whether there are loads present, at least in jurisdictions
where I have worked. I've heard that some inspectors will allow you to
ignore it if it is labeled as a PV combiner with "add no loads"
notation.\u201d<br>
<br>
NEC 705.12 (D) states that the distribution equipment (in this case the
combiner panel, fed by multiple inverters and a utility source) must be
\u201ccapable of supplying multiple branch circuits or feeders or both\u201d
for (D)(1) through (7) to apply. If you fully populated a combiner panel
with inverter breakers, leaving no slots for load breakers, it is not
capable of supplying branch circuits or feeders, and IMO the 120% rule
does not apply to the combiner buss or the conductors back to its point
of utility interconnect. I have argued this point as well as label
combiners \u201cload circuits prohibited\u201d (with or without available
slots) and received AHJ approval.<br>
<br>
You could also just lock shut a combiner that had spare slots as a
deterrent to adding load breakers.<br>
<br>
<br>
Kirk Herander<br>
VT Solar, LLC<br>
dba Vermont Solar Engineering<br>
NABCEP<sup>TM </sup>Certified installer Charter Member<br>
NYSERDA-eligible Installer<br>
VT RE Incentive Program Partner<br>
802.863.1202<br>
<br>
<b>From:</b> re-wrenches-bounces@lists.re-wrenches.org
[<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" eudora="autourl">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b>Jason Szumlanski<br>
<b>Sent:</b> Tuesday, June 26, 2012 8:28 AM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] Enphase grid tie question<br>
<br>
I'll email you off-list a 1-line diagram from a system with 164
microinverters broken down into 8 strings in a 208V system. This
particular system used two subpanels to accumulate PV, but that was only
because we had to backfeed two existing subpanels due to the size of
existing 480/208V transformers. You will have to look at the utility
service and all existing equipment.<br>
<br>
Regarding the breakers in the subpanel, you will only need a maximum of a
20A breaker for each string. The max inverters per string is 25 and the
calculation for OCPD is:<br>
<br>
215W / 208V x 25 inverters / 1.732 x 1.25 = 18.65A<br>
<br>
\u201cYou DO need to observe the 120% rule for the combining subpanel,
regardless of whether there are loads present, at least in jurisdictions
where I have worked. I've heard that some inspectors will allow you to
ignore it if it is labeled as a PV combiner with "add no loads"
notation.\u201d<br>
<br>
Use a MLO panel with a fusible disconnect between the subpanel and the
interconnection point. If you use a 225A panel, you can feed it with
270A. With eight 20A backfed PV circuits, you would need to protect the
line side of the panel with a 100A fusible disconnect. That probably
isn't going to work. You may be best off from a cost perspective using
two 225A subpanels and two 60A fusible disconnects. Anything larger than
a 60A 3P disconnect and the price skyrockets. It all depends on your
circuit calculations and the existing equipment. Of course, you would
need two spaces for your interconnection point.<br>
<br>
Jason Szumlanski<br>
Fafco Solar<br>
<br><br>
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