[RE-wrenches] EGC ground impedance

[Bill Brooks]

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 <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

 

 

 

 

 

 



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