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<DIV><FONT size=2 face=Arial>I agree with Kelly and others that all grounding
electrodes should be bonded together. My experience in lightning country
with PV systems with a ground rod at the array and separate ground rod
at the BOS and no wire connecting the ground rods has always resulted
in fried equipment. The same systems, after they were repaired and the ground
rods were connected together, survived every lightning storm for several
years. I have found that the same holds true for any equipment or
structure - good earth grounds all connected together create a grounding field
and can create a cone of protection. Properly grounded equipment with all
grounding electrodes connected together generally survive lightning storms
and have been known to survive direct lightning strikes.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Joel Davidson</FONT></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=bcrise@nietc.org href="mailto:bcrise@nietc.org">Brian Crise</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=re-wrenches@lists.re-wrenches.org
href="mailto:re-wrenches@lists.re-wrenches.org">RE-wrenches</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, June 05, 2009 1:45 PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [RE-wrenches] 690.47D
(revisited)</DIV>
<DIV><BR></DIV>Kelly,
<DIV>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).
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</DIV>
<DIV>Hopefully this helps,</DIV>
<DIV>Brian</DIV>
<DIV><BR></DIV>
<DIV>NABCEP Certified PV Installer</DIV>
<DIV><BR></DIV>
<DIV>To contact Brian L Crise:</DIV>
<DIV>
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face=Helvetica>16021 NE Airport Way</FONT></P>
<P style="MARGIN: 0px"><FONT style="FONT: 12px Helvetica" size=3
face=Helvetica>Portland OR, 97230</FONT></P>
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face=Helvetica>e-mail:<SPAN class=Apple-converted-space><SPAN
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<DIV>
<DIV>On Jun 5, 2009, at 12:10 PM, Kelly Keilwitz, Whidbey Sun & Wind
wrote:</DIV><BR class=Apple-interchange-newline>
<BLOCKQUOTE type="cite">
<DIV>Mark, <BR>I don't think that the 690.47D "PV GE" is part of the
premises AC & DC<BR>ground electrode system.<BR><BR>IMO, in order to
function to properly as enhanced protection from lightning<BR>induced
surges as described in the 690.47(D) section note in the 2008
NEC<BR>Handbook, the optional supplementary grounding electrode should not
be<BR>connected to the premises system AC and DC grounding electrodes, as
shown in<BR>Exhibit 690.6 of the Handbook. If an additional #8 (per 250.166)
is bonded<BR>to the premises AC/DC system GE, it's path will be parallel
with, and<BR>redundant to, the existing EGC. This could set up the potential
for an<BR>inductive ground loop, which might cause more damage to the system
during a<BR>lightning strike than it would prevent.<BR><BR>If the
additional electrode for array grounding (PV GE) of 690.47D is
not<BR>required, then the PV GEC of that section should not be
required.<BR><BR>Of course, these opinions are academic. What I really want
to know is what<BR>the AHJ's think! Any of you have to deal with this,
yet?<BR><BR>Thanks,<BR>-Kelly<BR><BR>Kelly Keilwitz, P.E.<BR>Whidbey Sun
& Wind, LLC<BR>Renewable Energy Systems<BR>NABCEP Certified PV
Installer<BR>WA Electrical Administrator #KEILWKM923RB<BR>987 Wanamaker
Rd.<BR>Coupeville, WA, 98239<BR>360.678.7131<BR><A
href="mailto:sunwind@whidbeysunwind.com">sunwind@whidbeysunwind.com</A><BR>WA
Electrical Contractor #WHIDBSW920MS<BR>WA General Contractor
#WHIDBSW946M1<BR><BR><BR><BR><BR>On 6/5/09 10:01 AM, "Mark Frye"
<markf@berkeleysolar.com> wrote:<BR><BR>
<BLOCKQUOTE type="cite">Kelly,<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite"><BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">The question is, if the AJH had required you to
run the new array DC GEC<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">directly to an additional DC array GE, would that
new DC GE system need to<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">be bonded with the exisitng AC GE system with a
bonding wire other than the<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">new EGC running from the array to new DC
GE?<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite"><BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">Unfortunately, NEC 2008 is not clear about this
with respect to the new DC<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">array GE. That leaves us with only the
general NEC requirement that all<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">premise GE's be bonded into a single
system.<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite"><BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">So the total effect of the new 690.47D, assuming
that the "prcaticable"<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">location for the new DC array GE is not within 6
ft of the exisiting AC GE,<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">is this:<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite"><BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">A new DC array GEC must run directly from the
array to a new DC GE system<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">and and a new bonding jumper must be run from the
new DC GE system to the<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">exisitng AC GE system.<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite"><BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">It the new DC GE system can be the same as the
existing AC GE by virtue of<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">it proximity (less than 6 ft) to the practiable
location, then the ne DC<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">array GEC must still be run directly to exist GE
system which is now the<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">AC/DC GE system.<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite"><BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite"><BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">Mark Frye<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">Berkeley Solar Electric Systems<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">303 Redbud Way<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">Nevada City, CA 95959<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">(530) 401-8024<BR></BLOCKQUOTE>
<BLOCKQUOTE type="cite">www.berkeleysolar.com<BR></BLOCKQUOTE>
<BLOCKQUOTE
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