[RE-wrenches] EGC ground impedance

Wed Jan 15 13:29:15 PST 2014

Gary - The tool is designed to measure the ground impedance for a grounding
electrode by measuring the impedance through the earth and back through the
service ground (which is assumed to have near zero impedance).  I think it
induces a current in the conductor and determines how much EMF it takes to
push those electrons (R = V / I).  For this to work it only measures a
single connection to earth, and all other connections to earth are
basically the return path.  I was trying to use it on a system without a
return path so it makes sense that I was getting a high reading.

For a brighter energy future,

Andrew Truitt

Principal
Truitt Renewable Energy Consulting, LLC

(202) 486-7507

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

 <%28202%29%20486-7507>

[image: 24 copy.jpg]

"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 Wed, Jan 15, 2014 at 7:03 PM, Bill Brooks <billbrooks7 at yahoo.com> wrote:

> 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:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *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
>
> 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
>
> [image: 24 copy.jpg]
>
> "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 <billbrooks7 at yahoo.com>
> wrote:
>
> Andy,
>
>
>
> How are you testing the ground impedance of the EGC?
>
>
>
> Bill.
>
>
>
> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *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
>
> 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
>
> [image: 24 copy.jpg]
>
> "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
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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