Related to the recent thread on ground rod drivers is the question of
what to do when you _can't_ drive them because you have rock near the
surface. The following answers are from Reginald (Reggie) Driscoll
WA6ZAP:
For a start, read National Electrical Code Article 250 - Grounding,
re: Earth Electrodes and the requirements.
If you decide to dig a trench and have the space, I would recommend as long
of a horizontal ground electrode as space permits.
Your local Library probably has a copy of the National Fire Protection Code,
the National Electrical Code is a subsection of the National Fire Protection
Code.
If my memory is correct, the National Fire Protection Code is about 3 or 4
large volumes 8-1/2 x 11. Generally, it kept in the Reference Section of the
Library.
Some specific cites:
250-52(c)
Specifies if you can not drive an 8 foot rod vertically 8 feet into the
ground to can drive it at up to a maximum of 45 degree from vertical. The
other alternative is to dig a trench 30 inches deep and bury the 8 foot rod
horizontal.
250-52(c)
Rod and pipe electrodes shall not be less than 8 feet in length, shall
consist of the following materials and shall be installed in the following
manner.
1. Electrodes of pipe or conduit shall not be less than 3/4 inch trade size
and where of iron or steel, shall have the outer surface galvanized or
otherwise metal-coated for corrosion protection.
2. Electrodes of rods of iron or steel shall be at least 5/8-inch diameter.
Stainless steel rods less than 5/8 inch in diameter, nonferrous rods, or
their equivalent shall not be less than 1/2 inch in diameter.
3. The electrode shall be installed such that at least 8 feet of length is
in contact with the soil. It shall be driven to a depth of not less than 8
feet except that, where rock bottom is encountered, the electrode shall be
driven at an oblique angle not to exceed 45 degrees from the vertical or
shall be buried in a trench that is not less than 2-1/2 feet deep. The upper
end of the electrode shall be flush with or below ground level unless the
aboveground end and the grounding electrode conductor attachment are
protected against physical damage as specified in Section 250-10."
Other sections of Article 250 also discuss the other acceptable earth
electrodes, bonding requirements, and acceptable methods and materials. Pay
special attention to the discuss on the other materials and methods that may
be use for earth electrodes.
Also take a read through Article 810 - Radio and Television Equipment, this
section discusses protection requirements.
Grounding and Bonding References
National Electrical Code (NEC)
Article 250 - Grounding
Article 810 - Radio and Television Equipment
The ARRL Antenna Book - 19th Edition
Chapter 1 - Safety First
Chapter 3 - The Effects of Ground
Chapter 27 - Antenna and Transmission-Line Measurements
The ARRL Handbook for Radio Amateurs 2001 - 78th Edition
Chapter 9 - Safety
Chapter 20 - Antennas & Projects
Chapter 22 - Station Setup and Accessory Projects
Chapter 28 - Electromagnetic Interference (EMI)
The ARRL RFI Book - 1st Edition
Chapter 2 - EMC Fundamentals
The "Grounds" for Lightning and EMP Protection - Second Edition 1993
Published by: PolyPhaser Corporation
Out of Print - replaced by: "Lightning Protection and Grounding
Solutions for Communications Sites"
Lightning Protection and Grounding Solutions for Communication Sites
-First Edition January 2000
Published by: PolyPhaser Corporation
May be ordered from:
Talley Communications
Hayward, CA
1-800-223-4949
Catalog No. LPGS
Cost: $24.44 including tax and shipping (April 2001 cost)
MIL-HDBK-419A - Grounding, Bonding, and Shielding for Electronic
Equipments and Facilities
An excellent 812 pages reference on all aspects of grounding,
bonding, and shielding.
Available as a PDF file at:
http://astimage.daps.dla.mil/quicksearch/
Search for Document Id: MIL-HDBK-419A
Click on: Document ID: MIL-HDBK-419A
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