Daryl:
I apologize for my ignorance, but I can't seem to find this exception in
the 2008 code. Can you cite the section?
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.
Thanks,
William
At 06:44 PM 6/26/2012, you wrote:
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
I agree with Kirk
From: Kirk Herander <k...@vtsolar.com>
To: 'RE-wrenches' <re-wrenches@lists.re-wrenches.org>
Sent: Tuesday, June 26, 2012 3:53 PM
Subject: [RE-wrenches] combiners and the 120% rule
Jason,
In your email below you state:
âYou 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.â
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
âcapable of supplying multiple branch circuits or feeders or bothâ 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 âload
circuits prohibitedâ (with or without available slots) and received AHJ
approval.
You could also just lock shut a combiner that had spare slots as a
deterrent to adding load breakers.
Kirk Herander
VT Solar, LLC
dba Vermont Solar Engineering
NABCEPTM Certified installer Charter Member
NYSERDA-eligible Installer
VT RE Incentive Program Partner
802.863.1202
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jason
Szumlanski
Sent: Tuesday, June 26, 2012 8:28 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Enphase grid tie question
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.
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:
215W / 208V x 25 inverters / 1.732 x 1.25 = 18.65A
âYou 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.â
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.
Jason Szumlanski
Fafco Solar
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