[RE-wrenches] grounding the Enphase inverter

[Bill Brooks]

All,

While there is ambiguity in the 2008 NEC in 690.47(C) on the requirements
for system grounding of PV systems, the 2011 NEC in 690.47(C) clarifies the
intent. 

While an application note from Enphase may state that WEEBs can be used as
part of the grounding electrode system, I disagree with this concept and do
not believe it meets the requirements or intent of the NEC as clarified in
the 2011 NEC. The problem with a grounded PV inverter is that it requires a
grounding electrode conductor (GEC) from the grounding point (on the
inverter) to the grounding electrode. The 2008 and 2011 NEC allows for that
connection to be terminated at the grounding bar in the service panel
supplying the micro-inverters.

There is no problem with using the WEEB to bond the rails to the modules and
then to the Enphase Micro-inverter. From the micro-inverter, a bare 6AWG
could be run to pick up each micro-inveter in each row of micro-inverters
with splices made to a single bare 6AWG made with irreversible splices. At
the rooftop junction box, the GEC could be irreversibly spliced to an 8AWG
green insulated conductor to run unbroken to the grounding busbar in the
service equipment.

While this may not be in agreement with the Enphase application note, I
believe it meets the intent and letter of the NEC as clarified in the 2011
NEC 690.47(C). While using the WEEBs in the GEC circuit may not cause a life
or death issue, it is absolutely open to being questioned by the electrical
inspector. If the electrical inspector decides it is wrong--it is wrong. If
you or the field inspector appeals to me or an expert like John Wiles, we
will state what I have stated above. Then you would have to remove all the
modules, throw away the WEEBs, put in new WEEBs with the new bare copper
6AWG and reinstall the modules--it just ain't worth it.

690.47(D) was removed from the 2011 NEC because it was primarily for
lightning protection (not a safety issue according to the NEC) and was
ambiguously worded with respect to residential rooftop PV systems. If the
local jurisdiction requires the additional electrode, install a j-box at the
point near ground-level where the conduit transitions from vertical to
horizontal and install an irreversibly spliced bare 6AWG to run from the
j-box to a ground rod below the j-box--mildly painful, but very doable.

Bill.

Bill Brooks, PE
Principal
Brooks Engineering
873 Kells Circle
Vacaville, CA 95688
707-332-0761 (office and mobile)
707-451-7739 (fax)
bill at brooksolar.com (email)
www.brooksolar.com (web)



-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jason
Szumlanski
Sent: Thursday, March 03, 2011 12:55 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] grounding the Enphase inverter

I don't see it in your comments. At least that wasn't clear. Anyway, in
that case there is absolutely no reason to use the inverter ground clip.
The whole purpose of the inverter-> rail WEEB is to eliminate the ground
wire.

Take a look at the Enphase App Note here:
http://www.enphaseenergy.com/downloads/EnphaseAppNote_WEEB_Installation.
pdf

It starts out, "As an alternative to installing a continuous grounding
electrode conductor connected to each microinverter chassis, a grounding
washer may be used to ground the microinverter to grounded racking." It
couldn't be more clear for an inspector, but I understand that sometimes
it's hard to convince them. Hope this helps!

Jason Szumlanski
Fafco Solar

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kirk
Herander, VSE
Sent: Thursday, March 03, 2011 8:46 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] grounding the Enphase inverter

"As an aside, why didn't you use approved WEEB's to bond the inverters
to
the rails? This eliminates the ground wire to each inverter. Simpler
IMHO."

I did. It is in my comments.

Kirk Herander
Vermont Solar Engineering
802.863.1202
NABCEP(tm) Certified Solar Installer
NYSERDA-eligible Installer
VT Solar Incentive Program Partner