[RE-wrenches] 690.47D (revisited)

[Mark Frye]

 Thanks Kelly,

I haven't gotten the handbook, but I think I am getting the picture.

How nice of the handbook to let us know that the new GE and GEC that "shall
be installed" according to 690.47D is nothing more than an "optional
supplementary ground electrode".  And furher, if you do choose to take the
option of installing it, in order to have the best lightning protection, you
don't have to bond it to the exisiting GE system. How easy to now disregard
250.106 which says that 'The lightning protection system ground terminals
shall be bonded to the building or structure grounding electrode system".

Considering the inherant problems of 690.47D, I can certainly understand any
AJH trying to avoid this issue of the creation of a whole new class of GE's
who's use falls completely outside the basic definitions of 250  III 250.50,
"All grounding electrodes.....shall be bonded together to form the grounding
electrode system."

MPF
 
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 Kelly
Keilwitz, Whidbey Sun & Wind
Sent: Friday, June 05, 2009 12:11 PM
To: RE Wrenches listserve
Subject: Re: [RE-wrenches] 690.47D (revisited)

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