Andy,
Larger cable tray systems have expansion joints (125 feet or more). If bonding jumpers are not placed around these joints, you will get a high reading. However, it may just be that your meter is flaking out with the long path to earth. I would try another meter before I would believe your high readings. Bill. From: [email protected] [mailto:[email protected]] On Behalf Of Andrew Truitt Sent: Tuesday, January 14, 2014 8:55 PM To: RE-wrenches Subject: Re: [RE-wrenches] EGC ground impedance Bill - I'm using an Amprobe DGC-1000A. I let it self-calibrate and then simply clamp it on to a conductor, and it reads the impedance to ground (http://content.amprobe.com/manualsA/DGC1000.pdf). I used it on a well grounded RBI system (driven piles) a few months ago and it measured ground impedances of less than 25 Ohms for all EGCs, as expected for a system with so much contact between the metal structure and earth. Ray - The tray does make a good conductor. I did some more testing and any point along the tray itself gives less than 10 Ohms; its only the #10 conductors between the array and the tray where the impedance spikes. The conductors are bonded to the tray with torqued, star-washered, copper/stainless lay-in lugs. There are no ground rods in the system due to the requirements of the capped landfill, but there is a UFER ground at the equipment pad that gives readings of < 1 Ohm for the GEC. For a brighter energy future, Andrew Truitt Principal Truitt Renewable Energy Consulting, LLC (202) 486-7507 <tel:%28202%29%20486-7507> LinkedIn Profile <http://www.linkedin.com/pub/andrew-truitt/8/622/713> Company Website <http://truittreconsulting.weebly.com/> NABCEP Certified PV Installation Professional ID: 032407-66 Colorado Journeyman Electrician License No.: 600132 "Don't get me wrong: I love nuclear energy! It's just that I prefer fusion to fission. And it just so happens that there's an enormous fusion reactor safely banked a few million miles from us. It delivers more than we could ever use in just about 8 minutes. And it's wireless!" ~William McDonough On Tue, Jan 14, 2014 at 10:47 PM, Bill Brooks <[email protected] <mailto:[email protected]> > wrote: Andy, How are you testing the ground impedance of the EGC? Bill. From: [email protected] <mailto:[email protected]> [mailto:[email protected] <mailto:[email protected]> ] On Behalf Of Andrew Truitt Sent: Tuesday, January 14, 2014 7:25 AM To: RE-wrenches Subject: [RE-wrenches] EGC ground impedance Wrenches - What do you consider to be a safe ground impedance for a PV array equipment grounding conductor? NEC2011 250.53(A) says that if the impedance between the grounding electrode and earth is less than 25 ohms then no supplementary grounding electrode is needed, but I'm not clear on what that means for the ground impedance measurement within the array. For example, I am inspecting a ballasted landfill system (i.e. no penetrating the earth allowed - just a UFER at the equipment pad) where the ground impedance at the GEC is very low (<1 Ohm), but the array EGCs are showing ground impedances of between 500 and 1000 Ohms. The EGCs (#4) are connected to Cope cable trays, which are in turn connected to the inverter grounding bar via #4 bonding jumpers. The cable tray is grounded per manufacturer specs (large bonding jumpers at each joint), but the runs can be quite long (300'+) with many connections, though nothing appears to be loose. I intend to recommend that continuous conductors be installed to reduce array ground impedance, but any input on the issue would be very much appreciated. For a brighter energy future, Andrew Truitt Principal Truitt Renewable Energy Consulting, LLC (202) 486-7507 <tel:%28202%29%20486-7507> LinkedIn Profile <http://www.linkedin.com/pub/andrew-truitt/8/622/713> Company Website <http://truittreconsulting.weebly.com/> NABCEP Certified PV Installation Professional ID: 032407-66 Colorado Journeyman Electrician License No.: 600132 "Don't get me wrong: I love nuclear energy! It's just that I prefer fusion to fission. And it just so happens that there's an enormous fusion reactor safely banked a few million miles from us. It delivers more than we could ever use in just about 8 minutes. And it's wireless!" ~William McDonough _____ <http://www.avast.com/> This email is free from viruses and malware because avast! Antivirus <http://www.avast.com/> protection is active. _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] <mailto:[email protected]> Change email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> Check out participant bios: www.members.re-wrenches.org <http://www.members.re-wrenches.org> --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
<<image003.jpg>>
<<image004.jpg>>
_______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Change email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
