Kelly, 

I always install a grounding electrode at the array. I always run a continuous 
(not spliced), properly sized, or oversize (usually #4), bare, copper conductor 
from the array modules and frame, to that electrode, then continue it, 
direct buried, to all of the other grounding electrodes in the system. 

I DO NOT run a separate equipment grounding conductor (EGC) with the array 
circuit conductors, for the reason you mention. I don't want to create a ground 
loop. I also want to keep any energy from lightning away from the circuit
conductors. 
Here in Vermont, we get our share of lightning and I've seen way too much
equipment 
that's been fried.

The NEC, in article 250 permits the EGC, IN DC CIRCUITS ONLY, to be run
SEPARATELY
from the DC circuit conductors. In the method above, the direct buried, bare
conductor
serves as BOTH the EGC and the GEC for the array.

In the premier issue of Solar Pro Magazine, 
<http://solarprofessional.com/article/?file=SP1_1_pg28_3Phase>
Bill Brooks, John Wiles and I took turns trying to make sense of 690.47.
I'm not sure we succeeded. :-)

There are no residential inspections in VT. 
Hope this helps.

Dick

 
-- You wrote:
Brian,

Thanks for your thoughts. Have you changed your installations to meet
690.47D? If, so, how?

On 6/5/09 1:45 PM, "Brian Crise" <bcrise@nietc.org> wrote:

> Kelly,
> It is my understanding that all types of grounding electrodes, whether
> supplementary or not, for lightning protection or PV array grounding shall be
> bonded together to form the grounding electrode system. (250.106, 690.47(A)
> which sends you to 250.50,   NFPA 780-2008 4.14).

Except that the requirements of 690 supercede any other sections, if there's
a conflict. 690.47(A) is for AC PV systems.

>If you do not do this and
> you do get a lightning strike or for that matter any high frequency signal
> injected onto a grounding electrode you will get what they call a ground
> potential rise onto one part of the system.  With the other separate grounding
> electrode not having this same signal because of them not being common, you
> will have a potential difference between the two separate electrodes even
> though they are both in the ground.  The ground (earth) is actually a very
> poor conductor when it comes to high levels of high frequency current.

I'm with you, here, IF the supplementary PV GE is required it makes sense to
bond it to the others (even though the Handbook doesn't show it). We have
been running a bare #6 Cu GEC from remote ground mounts to the GE system
near the inverter for years.

However, it DOESN'T make sense to me to run this redundant (to the EGC) PV
GEC when the the supplementary PV GE is NOT required.


> Hopefully this helps,
> Brian
> 
> NABCEP Certified PV Installer
> 
> To contact Brian L Crise:
> Address:
> 16021 NE Airport Way
> Portland OR, 97230
> Office Phone:    (503) 262-9991 x.5054
> e-mail:    bcrise@nietc.org
> 
> 
>  
> 
> On Jun 5, 2009, at 12:10 PM, Kelly Keilwitz, Whidbey Sun & Wind wrote:
> 
>> Mark, 
>> I don't think that the 690.47D "PV GE" is part of the premises AC & DC
>> ground electrode system.
>> 
>> IMO, in order to function to properly as "enhanced protection from lightning
>> induced surges" as described in the 690.47(D) section note in the 2008 NEC
>> Handbook, the "optional supplementary grounding electrode" should not be
>> connected to the premises system AC and DC grounding electrodes, as shown in
>> Exhibit 690.6 of the Handbook. If an additional #8 (per 250.166) is bonded
>> to the premises AC/DC system GE, it's path will be parallel with, and
>> redundant to, the existing EGC. This could set up the potential for an
>> inductive ground loop, which might cause more damage to the system during a
>> lightning strike than it would prevent.
>> 
>> If the "additional electrode for array grounding" (PV GE) of 690.47D is not
>> required, then the PV GEC of that section should not be required.
>> 
>> Of course, these opinions are academic. What I really want to know is what
>> the AHJ's think! Any of you have to deal with this, yet?
>> 
>> Thanks,
>> -Kelly
>> 
>> Kelly Keilwitz, P.E.
>> Whidbey Sun & Wind, LLC
>> Renewable Energy Systems
>> NABCEP Certified PV Installer
>> WA Electrical Administrator #KEILWKM923RB
>> 987 Wanamaker Rd.
>> Coupeville, WA, 98239
>> 360.678.7131
>> sunwind@whidbeysunwind.com
>> WA Electrical Contractor #WHIDBSW920MS
>> WA General Contractor #WHIDBSW946M1
>> 
--- end of quote ---

