[RE-wrenches] What is a "direct-current system"?

[R. Walters]

690.47(C) applies to almost all our solar work (anything with an  
inverter). The whole point is: where does the equipment grounding  
conductor EGC become the grounded electrode conductor GEC? At that  
point and down, 250.166 applies as well. IMHO, once the separate  
modules are bonded to a center grounding point at or very near the  
array framing, then the conductor to the required supplementary  
electrode is the GEC. (which can be the framing, if 250.52 is followed.)
A separate EGC sized by 250.122 connects this center array grounding  
point back along with the power conductors to the AC ground buss ,  
which is bonded to the house's GEC to a separate electrode.
These electrodes are connected through the EGC, and therefore satisfy  
250.54 and ultimately 250.4.

They should not be connected by a 2nd pathway, as this creates a  
ground loop.
Connecting the various electrodes through EGC system alone satisfies  
both the requirements of the NEC, and good lightning protection  
practice of a single connection point grounding system with no loops.
Lightning strikes are conducted directly to earth at multiple points  
in the system by their separate large GECs while decoupling parts of  
the system somewhat from surges (via the reduced size EGC), but still  
bonded, insuring that no potential exists in different parts of the  
ground system normally.

Ok I'm going home
R. Walters
Solarray.com
NABCEP # 04170442	



On Jun 19, 2009, at 12:22 PM, Peter Parrish wrote:

> Thanks. One last thing: 690.47(C) has its own set of grounding  
> requirements (C)(1)-(8). So we need to follow those as apposed to  
> 250-166?
>
>
> - Peter
>
>
>
>
>
> <image002.gif>Peter T. Parrish, Ph.D., President
> California Solar Engineering, Inc.
> 820 Cynthia Ave., Los Angeles, CA 90065
> CA Lic. 854779, NABCEP Cert. 031806-26
> peter.parrish at calsolareng.com
> Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
>
>
> From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches- 
> bounces at lists.re-wrenches.org] On Behalf Of R. Walters
> Sent: Friday, June 19, 2009 10:50 AM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] What is a "direct-current system"?
>
>
> I just sort of hit this  in a previous post:
>
> check 690.47C(3). Your system falls under (C) AC & DC grounding  
> requirements.....
>
> This just shouldn't be that hard with the inspectors....
>
>
> R. Walters
>
> Solarray.com
>
> NABCEP # 04170442
>
>
>
>
>
>
> On Jun 19, 2009, at 10:55 AM, Peter Parrish wrote:
>
>
>
>
> I have a LA Dept. of B&S inspector cite Article 690.47(B) “Direct- 
> Current Systems” and its consequent grounding requirements (250.166 
> (A)(B)) in connection with a very straightforward grid tied PV  
> system (i.e. no batteries, just PV and a Xantrex GT inverter).
>
>
> He said that since there is a DC circuit as well as an AC circuit,  
> 690.47(B) applies. I countered that all PV systems have a DC  
> circuit, so to separately call out a “Direct-Current System” must  
> apply to something other than the DC PV circuit inherent in all PV  
> systems.
>
>
> Am I missing something here? Is “Direct-Current System” defined in  
> Article 690? We are working off NEC 2008.
>
>
> Thanks in advance for your help.
>
>
> -          Peter
>
>
> <image003.gif>Peter T. Parrish, Ph.D., President
> California Solar Engineering, Inc.
> 820 Cynthia Ave., Los Angeles, CA 90065
> CA Lic. 854779, NABCEP Cert. 031806-26
> peter.parrish at calsolareng.com
> Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
>
>
>
> <image003.gif>
>
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