I agree with Jason that the panel, as described, would be capable of
supplying multiple branch circuits and could be deemed non-compliant,
but I've found inspectors here to be reasonable about this practice.
It's perfectly safe to add a branch circuit, even multiple ones, to an
ac combiner. As long as it is for operating associated equipment such as
communications devices like the Envoy, or data loggers, or power to
operate a tracker controller and motor, it should be allowed.
Consider a 100-amp panel being used as an ac combiner with four 20-amp
circuit breakers being backfed with micro-inverters. A few small loads
on this panel just lowers the current on the bus bars. The risk that the
120% rule is supposed to address is the possibility of overloading the
bus bars. In the case of the ac combiner that could happen if someone
were to add some very large loads to it.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
t: 541-568-4882
On 7/1/2012 6:46 AM, Jason Szumlanski wrote:
Well, if you install a bunch of 2-pole breakers for the.inverters, and
then add a single pole breaker for the Envoy, there is definitely one
space left and the panel would be "capable" of supplying additional
branch circuits.
Just being devil's advocate here... I'm with you, but we need more
clarity and less room for interpretation on this matter.
Jason Szumlanski
Fafco Solar
On Sat, Jun 30, 2012 at 5:09 PM, Kirk <k...@vtsolar.com
<mailto:k...@vtsolar.com>> wrote:
I would argue a single dedicated load circuit for the Enphase
Envoy, in a dedicated inverter combiner panel, is code legal. Why?
Because 705.12 states the distribution equipment must be capable
of supplying "multiple branch circuits" for the 120% rule to
apply. A single dedicated circuit for the Envoy appears to
comply. Use a load center with a lockable cover if there are extra
slots and you have done due diligence.
Kirk Herander
VSE
On Jun 27, 2012, at 11:51 AM, Jason Szumlanski
<ja...@fafcosolar.com <mailto:ja...@fafcosolar.com>> wrote:
If you install a combiner panel that can supply additional branch
circuits, it becomes part of the building distribution system.
Note that Enphase recommends you install a branch circuit to
supply power to the Envoy device right from the combiner panel.
If that is the case, the panel is certainly part of the building
distribution system and is obviously capable of supplying branch
circuits, in which case the 120% rule would apply. I don't like
it and I don't necessarily agree with it, but based on my strict
interpretation of the code I can see why an AHJ would require
application of this section in this case.
Jason Szumlanski
Fafco Solar
On Wed, Jun 27, 2012 at 10:59 AM, Chris Mason
<cometenergysyst...@gmail.com
<mailto:cometenergysyst...@gmail.com>> wrote:
I don't think this is expressed in the code, but in my
opinion, the 120% applies to the building distribution
equipment, not to parts of the solar system. In the case
where a panel is being used to combine multiple inverter
outputs, the panel is part of the solar system only. The 120%
rule was an accommodation to allow solar to feed a building
distribution panel and is not applicable to solar system
components. It would be good if the code could indicate this
more clearly.
On Wed, Jun 27, 2012 at 8:29 AM, Jason Szumlanski
<ja...@fafcosolar.com <mailto:ja...@fafcosolar.com>> wrote:
Kirk,
That's basically what I said. Unfortunately, your opinion
holds no weight with my local AHJ's. I've argued the
point till blue in the face. Although, I have never had
the instance where all available slots were filled in the
combiner panel - I might be able to argue that case
successfully.
Jason Szumlanski
Fafco Solar
On Tue, Jun 26, 2012 at 4:53 PM, Kirk Herander
<k...@vtsolar.com <mailto:k...@vtsolar.com>> wrote:
Jason,
In your email below you state:
"You 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."
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 "capable of
supplying multiple branch circuits or feeders or
both" 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
"load circuits prohibited" (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
NABCEP^TM Certified installer Charter Member
NYSERDA-eligible Installer
VT RE Incentive Program Partner
802.863.1202 <tel:802.863.1202>
*From:*re-wrenches-boun...@lists.re-wrenches.org
<mailto:re-wrenches-boun...@lists.re-wrenches.org>
[mailto: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
"You 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."
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
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches@lists.re-wrenches.org
Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out participant bios:
www.members.re-wrenches.org
