[RE-wrenches] EGC ground impedance

Wed Jan 15 07:32:23 PST 2014

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!

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 4:54 AM, Andrew Truitt <atruitt at gmail.com> wrote:

> 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
>
>  <%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 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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