Grounding on rock [RE-wrenches]

David Brearley david at meridiansolar.com
Thu Sep 28 15:02:46 PDT 2006


Jim,

Bedrock is common here in Austin, especially the west side of town.  The
local code used to require a 20' coil of #2 bare copper in a 24" x 24" x 30"
deep hole.  Where we have bedrock we rent electric or even pneumatic
sledgehammers and go to town for as many hours as it takes.  Most inspectors
locally require encasing these electrode coils in a sack of concrete.

The local electrical ordinance changed recently to require a 12" x 24" by
1/4" thick copper plate in place of the copper coil.  These electrode plates
are available from our local supply house.  But just like the coil, it
requires a sledgehammer and a 30" deep hole.  

David Brearley
NABCEP Certified Solar PV System Installer (TM)
 
Meridian Energy Systems
2300 S. Lamar, Suite 107
Austin, TX 78704
512-448-0055 (ph)
512-448-0045 (fax)
www.meridiansolar.com


-----Original Message-----
From: Jim Duncan [mailto:ntrei at earthlink.net] 
Sent: Thursday, September 28, 2006 4:48 PM
To: RE-wrenches at topica.com
Subject: Grounding on rock [RE-wrenches]


Wrenches,
I won't be able to drive a ground rod due to the bedrock being less than 
a foot below the surface. A quick review of the NEC suggested ground 
plates as one option. Calling local supply houses turned up no one with 
such a device. The internet showed a clever ground lattice of rivited 
copper clad metal strips formed in a grid; available from India. 
Another product was a 20 foot long flat roll of copper sheet with a  #6 
copper lead welded to one end and a powdered compound to mix with water 
and pour in the trench to improve conductance. I'd be afraid to ask what 
that costs with the price of copper. 
A 20 foot #2 wire has to be at least 30 inches deep and, short of 
hauling in a truckload of dirt, there isn't 30 inches of dirt anywhere.
What sort of clever ideas have been used to solve this age old dilemma? 
As always, thanks

Jim Duncan
North Texas Renewable Energy Inc
Fort Worth, Texas
ntrei at earthlink.net
817.917.0527


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