[RE-wrenches] grounding the Enphase inverter

Fri Mar 4 12:05:19 PST 2011

Excellent post Mark. We spend way too much time as an industry worrying about these mundane grounding (and over grounding) issues, when there are very little actual safety issues involved.
Meanwhile, we're missing the real safety problems. (recent commercial system fires??)
I can't wait for our industry to mature to the point that we treat grounding as other industries do. I don't see any technical reason (besides onerous NEC language) that would prevent us from safely grounding the Enphase inverters like any other permanently mounted AC appliance (#12 EGC on a 20A circuit, run with the conductors, forget about all the irreversible splices, ad nauseum)

I respect BIll's points, too, as he is laying down the actual law as currently written to keep us out of trouble with the AHJs. (Thanks BIll)
But, as with numerous other code issues over the years, the code needs to change to catch up with technology and the actual safety issues. 
(remember when we had to ground battery based inverters with a 4/0 cable? ugh!)

Let's all work together to make micro-inverter grounding more sensible too.

R. Walters
ray at solarray.com
Solar Engineer

On Mar 4, 2011, at 11:53 AM, Mark Frye wrote:

> 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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