<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">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><div apple-content-edited="true"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; "><br></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">Address:</font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">16021 NE Airport Way</font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">Portland OR, 97230</font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; "><br></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">Office Phone:<span class="Apple-converted-space"><span class="Apple-converted-tab"> <span class="Apple-converted-space"> </span></span></span>(503) 262-9991 x.5054</font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><br></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">e-mail:<span class="Apple-converted-space"><span class="Apple-converted-tab"> <span class="Apple-converted-space"> </span></span></span><a href="mailto:bcrise@nietc.org">bcrise@nietc.org</a></font></p></div><br class="Apple-interchange-newline"></span></div></span><br class="Apple-interchange-newline"> </div><br><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 type="cite"><br></blockquote><br><br>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address: RE-wrenches@lists.re-wrenches.org<br><br>Options & settings:<br>http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org<br><br>List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org<br><br>List rules & etiquette:<br>www.re-wrenches.org/etiquette.htm<br><br>Check out participant bios:<br>www.members.re-wrenches.org<br><br></div></blockquote></div><br></div></body></html>