[RE-wrenches] 690.47D (revisited)

[Kelly Keilwitz, Whidbey Sun & Wind]

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 ³enhanced protection from lightning
induced surges² as described in the 690.47(D) section note in the 2008 NEC
Handbook, the ³optional supplementary grounding electrode² 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 ³additional electrode for array grounding² (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 at whidbeysunwind.com
WA Electrical Contractor #WHIDBSW920MS
WA General Contractor #WHIDBSW946M1




On 6/5/09 10:01 AM, "Mark Frye" <markf at berkeleysolar.com> wrote:

> Kelly,
> 
> The question is, if the AJH had required you to run the new array DC GEC
> directly to an additional DC array GE, would that new DC GE system need to
> be bonded with the exisitng AC GE system with a bonding wire other than the
> new EGC running from the array to new DC GE?
> 
> Unfortunately, NEC 2008 is not clear about this with respect to the new DC
> array GE.  That leaves us with only the general NEC requirement that all
> premise GE's be bonded into a single system.
> 
> So the total effect of the new 690.47D, assuming that the "prcaticable"
> location for the new DC array GE is not within 6 ft of the exisiting AC GE,
> is this:
> 
> A new DC array GEC must run directly from the array to a new DC GE system
> and and a new bonding jumper must be run from the new DC GE system to the
> exisitng AC GE system.
> 
> It the new DC GE system can be the same as the existing AC GE by virtue of
> it proximity (less than 6 ft) to the practiable location, then the ne DC
> array GEC must still be run directly to exist GE system which is now the
> AC/DC GE system.
> 
> 
> Mark Frye
> Berkeley Solar Electric Systems
> 303 Redbud Way
> Nevada City,  CA 95959
> (530) 401-8024
> www.berkeleysolar.com
>