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Andrew:<br>
<br>
I'm confused by your answer about the required additional earth
connection. That's not described in the Operating Instructions for
the DGC-1000. Where on the clamp-on meter is the earth connection
made?<br>
<br>
Regards,<br>
<br>
Gary Willett<br>
Icarus Engineering LLC<br>
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<td>Re: [RE-wrenches] EGC ground impedance</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Date: </th>
<td>Wed, 15 Jan 2014 15:32:23 +0000</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">From: </th>
<td>Andrew Truitt <a class="moz-txt-link-rfc2396E" href="mailto:atruitt@gmail.com"><atruitt@gmail.com></a></td>
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<td>RE-wrenches <a class="moz-txt-link-rfc2396E" href="mailto:re-wrenches@lists.re-wrenches.org"><re-wrenches@lists.re-wrenches.org></a></td>
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<td>RE-wrenches <a class="moz-txt-link-rfc2396E" href="mailto:re-wrenches@lists.re-wrenches.org"><re-wrenches@lists.re-wrenches.org></a></td>
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<div>Bill - Ray (the owner of this tool) just explained to me
that in order for it to function properly it needs an
additional connection to earth to complete the circuit. I.e.,
my issue stems from user error. Thanks for the help Ray!
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<br>
<div class="gmail_quote">On Wed, Jan 15, 2014 at 4:54 AM, Andrew
Truitt <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:atruitt@gmail.com" target="_blank">atruitt@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">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 (<a
moz-do-not-send="true"
href="http://content.amprobe.com/manualsA/DGC1000.pdf"
target="_blank">http://content.amprobe.com/manualsA/DGC1000.pdf</a>).
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.
<div>
<br>
</div>
<div>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.</div>
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<span
style="color:rgb(56,118,29)">For
a brighter energy future,<br>
<br>
<br>
Andrew Truitt <br>
</span></p>
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<p class="MsoNormal"><span
style="color:rgb(56,118,29)">Principal<br>
Truitt Renewable Energy </span><span
style="color:rgb(56,118,29)">Consulting,
LLC</span></p>
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use in just about 8 minutes. And
it's wireless!"<br>
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~William McDonough</p>
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<div class="h5">On Tue, Jan 14, 2014 at 10:47 PM,
Bill Brooks <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:billbrooks7@yahoo.com"
target="_blank">billbrooks7@yahoo.com</a>></span>
wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px
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<span
style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Andy,</span></p>
<p class="MsoNormal"><span
style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></p>
<p class="MsoNormal"><span
style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">How
are you testing the ground impedance
of the EGC?</span></p>
<p class="MsoNormal"><span
style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></p>
<p class="MsoNormal"><span
style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Bill.</span></p>
<p class="MsoNormal"><span
style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></p>
<p class="MsoNormal"><b><span
style="font-size:11pt;font-family:Calibri,sans-serif">From:</span></b><span
style="font-size:11pt;font-family:Calibri,sans-serif"> <a
moz-do-not-send="true"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org"
target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[mailto:<a moz-do-not-send="true"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org"
target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b>Andrew Truitt<br>
<b>Sent:</b> Tuesday, January 14, 2014
7:25 AM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> [RE-wrenches] EGC
ground impedance</span></p>
<div>
<div>
<p class="MsoNormal"> </p>
<div>
<p class="MsoNormal">
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 <i>electrode</i> 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.</p>
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<p
class="MsoNormal"><span
style="color:rgb(56,118,29)">For a brighter energy future,<br>
<br>
<br>
Andrew Truitt </span></p>
</div>
<div>
<p
class="MsoNormal"><span
style="color:rgb(56,118,29)">Principal<br>
Truitt Renewable Energy Consulting,
LLC</span></p>
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class="MsoNormal">
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Professional
ID: 032407-66</span></p>
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style="color:rgb(20,125,186)"><br>
</span>"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!"<br>
<br>
~William McDonough</p>
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