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I think Gary may be overthinking this. If the micro-inverters have a
GEC lug then you'll need to run a GEC.<br>
<br>
If you run your GEC to a ground rod, then you don't need to use one
larger than #6 per 250.166(C). (note also (D) and (E) but they're
less useful to you here)<br>
<i><br>
Commentary:</i><br>
It makes no sense to me why the NEC can require a 0.9in diameter,
#600mcm GEC for some systems (not this one) per 250.166(B) and then
say "oh wait, you installed a single ground rod? Then a #6 is all
you need!" in 250.166(C). But it certainly makes our lives easier.<br>
<br>
If the building GE is not a ground rod, you could still run your #6
GEC to that new ground rod, and then bond that rod to the existing
electrode using whatever size jumper is required per 250.53 (which I
believe would also be a #6). This lets you keep that 300' run as a
#6 rather than a #4 or #2 that may be required otherwise.<br>
<br>
DKC<br>
<br>
<div class="moz-cite-prefix">On 2013/9/17 23:56, Gary Willett wrote:<br>
</div>
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<div class="moz-cite-prefix">Charlie:<br>
<br>
The answer depends on whether the "system" (modules and
micro-inverters) is "grounded" or "ungrounded". I think you are
describing a "grounded" system, but it's not totally clear based
on your issue description.<br>
<br>
If the micro-inverter is "transformer-less" the conductors are
not isolated between the DC-in and the AC-out. This requires the
micro-inverter to have no DC-side system ground. The
micro-inverter AC-side always requires an EGC.<br>
<br>
I am assuming that the PV modules are in close proximity to the
micro-inverters, and the 300' home-run is for the AC outputs of
the micro-inverters.<br>
<br>
Is either DC bus (PV+ or PV-) a grounded conductor, or are both
busses ungrounded? If the DC-side combiners and re-combiners
have OCPDs and disconnecting means for both PV+ and PV-, then
your system is considered to be "floating" or "ungrounded".<br>
<br>
If the system is "ungrounded", a GEC is not required on the
DC-side of the micro-inverter, and only an AC-EGC sized per NEC
690.45 is required.<br>
<br>
If the DC-side combiners and re-combiners have OCPDs and
disconnecting means for only one conductor (PV+ or PV-), then
your PV system is considered to be "grounded". If the system is
"grounded", the combined DC-GEC and AC-EGC sizing requirements
in NEC 690.47(C)(3) apply. The larger of the EGC (Table 250.122)
and GEC [250.166(B)] sizes will be required.<br>
<br>
More specifics on the PV module Vmpp and micro-inverter you're
dealing with would be helpful.<br>
<br>
Regards,<br>
<br>
Gary Willett<br>
Icarus Solar<br>
<br>
<br>
On 9/17/13 8:37 PM, Aladdin Solar wrote:<br>
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<div><font face="Arial" size="2">We will be installing a 40KW
grid-tied PV system that uses PV modules wired in parallel
as per the module manufacturer -- so it's a high amperage,
low voltage system on the DC side. 2 branches of about 3KW
of parallel wired modules each come together onto a DC bus.
The DC branch conductors are sized as 2AWG.</font></div>
<div> </div>
<div><font face="Arial" size="2">The inverter system provided by
the manufacturer consists of a number of UL1741 single phase
microinverters that all are powered off of the low voltage
DC bus. So there's a bunch of microinverters in parallel,
combined output is single phase power.</font></div>
<div> </div>
<div><font face="Arial" size="2">Those microinverters have a
ground lug labeled "GEC". You know where this is going...</font></div>
<div> </div>
<div><font face="Arial" size="2">Assuming we are following NEC
690.47(C)(3), we'll be treating this ground as GEC and
following all the GEC rules. My understanding is that
because the DC conductors within the array are 2AWG (NEC
250.166(B), we will need to connect all 12 branches and 6 DC
buses with continuous 2AWG and bring it all the way back
300' to where the AC GEC bond is located. We're getting a
lot of pushback from the electrical sub and even some
disagreement from the module manufacturer on this--no one's
ever seen a grounding conductor of this size being required
for this application.</font></div>
<div> </div>
<div><font face="Arial" size="2">Please don't get too bogged
down with understanding the low voltage, parallel module
spec and the massive number of microinverters involved. What
I'm looking for is confirmation that I am properly
understanding how the NEC GEC requirements apply, especially
to the GEC size.</font></div>
<div> </div>
<div><font face="Arial" size="2">Charlie Pickard<br>
NABCEP Certified PV Installation Professional ™<br>
Aladdin Solar, LLC<br>
</font></div>
<br>
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