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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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