[RE-wrenches] grounding the Enphase inverter

Kirk Herander, VSE kirk at vtsolar.com
Thu Mar 3 05:46:02 PST 2011


"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

-----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: Wednesday, March 02, 2011 6:56 PM
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

Anyway, what we are seeing in some jurisdictions is the requirement for
the additional grounding electrode (690.47(D)) even when there is a good
argument that the premises grounding electrode via the MDP is arguably
"as close as practicable." I think we've used Exception No. 2 about once
or twice.

What it basically looks like, assuming you bond inverters and panels to
rails using WEEBS, is [insert deep breath] a bare ground wire from the
additional grounding electrode up to the roof, through lay-in lugs
(WEEB-LUGS) on each rail, into a junction box, irreversibly crimped to a
#6 THWN-2 green, down to the premises GEC via the MDP ground bus bar,
hitting any metal enclosures and grounding bushings along the way. If
you are using D380's with a green ground in the AC Interconnect cable,
that get's irreversibly crimped in the J-box, too. The GEC can function
as the EGC, fortunately.

Some inspectors have wanted to see the ground rods tied together with
another wire, even if it means trenching around the entire building,
digging up driveways and sidewalks, and calling in 811. I've reached the
boiling point more than a few times over this stuff. And you're right -
none of it makes much sense...

I recently asked Jacob Michaels at Enphase if he could come up with an
application note that clarifies grounding requirements relative to NEC
2008 and 2011 once and for all. Circumstances will always dictate
requirements, but AHJ's, at least around here, often put a good deal of
weight on an App Note from a manufacturer. We'll see!


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: Wednesday, March 02, 2011 6:07 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] grounding the Enphase inverter

My AHJ is making me ground the Enphase inverters AND use a separate
equipment ground for modules / mounting rails.

The panel frames are grounded to mounting rails via WEEBS, rails are
grounded together using WEEB lay-in lugs and copper wire, this ground
wire
makes its way to AC panel gnd bar, where it is connected to ground rod
via
grounding electrode conductor, as normal.

AHJ insists I also install dedicated continuous ground wire from each
Enphase inverter gnd clip directly to the building GEC or to the ground
rod
itself. Mind you, the inverter enclosure, to which the gnd clip is
attached,
is already grounded to the mounting rails via WEEBs. So what I have done
is
created a parallel ground between the mounting rails and the GEC, a.k.a
a
ground loop, a.k.a. a current divider. Short circuit current from the
Enphase is going to be split between the two paths to ground.

The only way this grounding scheme makes any sense to me is if the
inverters
were totally isolated from the rails using a non-conductive tape or
washer
between the rail and inverter at point of attachment. Just removing the
WEEBS would not isolate the two. 
My AHJ is basically trying to apply the grounding rules of a string
inverter
(dedicated gnd directly from inverter to GEC) to a micro-inverter, but I
feel this method, aside from redundancy and T $ M, is little short in
the
"best practice" or "safest" categories.

I'd be interested in other takes on this. Thanks.




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


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