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<div class="moz-cite-prefix">I believe the cable tray will still be
an excellent conductor, as long as the jumper connections are
tight. If you look at the cross sectional area of it, its
probably the equivalent of some fairly burly cable. Also the
jumpers are just part of the connection, If you removed a jumper,
there is still quite a bit of contact surface. (I'm not
recommending that though) but you really have parallel
connections at each joint.<br>
The high ground impedance measurements are par for the course for
my measurements over the years. A 5/8" ground rod in loose (land
fill...) soil is going to be about that. It might be possible to
compact around the rods to improve that, and/ or add some mineral
rich soil amendments around the rods to improve the impedance as
well.<br>
(an old phone tech that worked for me used to cure ground problems
all the time by drinking lots of coffee, and then ahem, moisten
the soil with mineral rich fluid, ahem.)<br>
While it is a bit unnerving to measure ground impedances that
high, the overall grounding system has low impedance. Also,
consider that the ballast trays will offer some conductivity to
ground as well. Any way to measure some of the ballasts' ground
impedance?<br>
If you did add continuous conductors, just make sure that they are
connected in a radiating star pattern; don't create inductive
loops, or you really will have some voltage differential across
the grounding system in a lightning strike.<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 1/14/2014 8:24 AM, Andrew Truitt wrote:<br>
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cite="mid:CAKTVxmt-+isv+TidgHB0fAFaWBAt=g=aiq94UY1vgx3qAsfXdw@mail.gmail.com"
type="cite">
<div dir="ltr">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.
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<p class="MsoNormal"><span
style="color:rgb(56,118,29)">For a
brighter energy future,<br>
<br>
<br>
Andrew Truitt <br>
</span></p>
</div>
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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>
</div>
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<p class="MsoNormal"><span
style="color:rgb(56,118,29)"><a
moz-do-not-send="true"
href="tel:%28202%29%20486-7507"
value="+12024867507" target="_blank">(202)
486-7507</a></span></p>
<p class="MsoNormal"><a
moz-do-not-send="true"
href="http://www.linkedin.com/pub/andrew-truitt/8/622/713"
target="_blank">LinkedIn Profile</a></p>
<p class="MsoNormal"><a
moz-do-not-send="true"
href="http://truittreconsulting.weebly.com/"
target="_blank">Company Website<span><span></span></span></a></p>
<p class="MsoNormal"><span
style="color:rgb(56,118,29)"><span>NABCEP</span>
Certified PV Installation Professional
ID: 032407-66</span></p>
<p class="MsoNormal"><span
style="color:rgb(56,118,29)">Colorado
Journeyman Electrician License No.:
600132</span><br>
</p>
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<span style="color:rgb(0,102,0)"><a
moz-do-not-send="true"
href="tel:%28202%29%20486-7507"
target="_blank"><span
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<p><span style="color:rgb(20,125,186)"></span><span
style="color:rgb(20,125,186)"><img
src="cid:part5.04070604.07020607@solarray.com"
alt="24 copy.jpg" border="0" height="133"
width="200"></span><br>
<span 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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