[RE-wrenches] grounding the Enphase inverter

Nick Soleil nicksoleilsolar at yahoo.com
Fri Mar 4 17:19:37 PST 2011


Hi Mark, Ray, and wrenches:
    I agree that the grounding requirements can be onerous, but I have to 
interject that most generator manufacturers do specify a dedicated grounding 
electrode conductor.  Also, I do not feel that a #8 ground is too big.  Probably 
unnecessary 99% of the time, but with all the shorts and arced connections that 
I have found in j-boxes, I feel good about running a larger grounding conductor.
    With regard to the Enphase grounded with WEEB; which I have done many times, 
I would recommend spelling out the exact grounding method for the 
micro-inverters on the permit package.  We should have this issue resolved 
before installation begins.

 Nick Soleil
Project Manager
Advanced Alternative Energy Solutions, LLC
PO Box 657
Petaluma, CA 94953
Cell:   707-321-2937
Office: 707-789-9537
Fax:    707-769-9037




________________________________
From: Mark Frye <markf at berkeleysolar.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Fri, March 4, 2011 10:53:46 AM
Subject: Re: [RE-wrenches] grounding the Enphase inverter

Yes, but that comes from the assumption that the inverter constitutes a
seperately derived "system".

But if the only purpose or use of the DC power derived from the DC system is
to drive the AC side of the inverter, how closely does it realy resemble a
classic seperately derived system. As opposed to having the DC power source
actually run DC utilization equipment such as motors and appliances.

It is interesting that the very language in the code descibes the inverter
as "utility interactive". Is it really correct to describe a UL174 inverter
operating only in parrallel with the utility as a seperately derived system?

To what degree has the Code failed to reflect the evolution of technology?
Yes, battery-based inverter systems capable of powering a facility in the
absense of a utility power souce do in fact become a seperately derived
system which need to have a GEC. But to impose the same requirement on an
inverter which cannot possibly deliver power to anything other than a system
that already has a GEC seems to me to be a crude cookie cutter response to a
far more complex situation.

We have put the complexity into the inverters. Recogonizing this we see that
we don't need the complexity in wiring?

Mark Frye
Berkeley Solar Electric Systems
303 Redbud Way
Nevada City,  CA 95959
(530) 401-8024
www.berkeleysolar.com 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Bill Brooks
Sent: Friday, March 04, 2011 9:51 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] grounding the Enphase inverter

System grounding requirements.

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mark Frye
Sent: Friday, March 04, 2011 7:51 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] grounding the Enphase inverter

The interesting thing to me is the underlying assumption in the Code that a
GEC is requried for grid-tied inverters at all. Why isn't EG sufficient for
function and safety. 

Which of the following common electrical equipment has the same requirement:

UPS
Motors with regenerative energy disipators DC power supplies Standby
generators

??

Mark Frye
Berkeley Solar Electric Systems
303 Redbud Way
Nevada City,  CA 95959
(530) 401-8024
www.berkeleysolar.com 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Bill Brooks
Sent: Thursday, March 03, 2011 10:48 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] grounding the Enphase inverter

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)

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