[Towertalk] Burying ground rods horizontally

Thu, 28 Nov 2002 21:05:23 -0600

Keep in mind that while grounding in accordance with the NEC provides 
safety with respect to the 60 Hz power; it does not provide either RF 
ground or the kind of lightning protection ground that hams seek in 
connection with antennas and radio equipment.  A single 8 foot ground 
rod is not worth much for RF or for lightning dissipation sufficient to 
protect electronic equipment.  RF penetrates only a fraction of a 
wavelength into the earth.  Limiting the maximum voltage impressed on 
your equipment by a lightning strike requires bypassing that energy to a 
large volume of earth by multiple ground connections.  Earth is a lossy 
capacitor.  Lightning charges that capacitor, then leaks off.  The 
maximum voltage is reduced by increasing the capacitance into which it 
initially flows.  V = Q/C, where Q is the charge in coulombs and C is 
the capacitance in Farads.

73 de WOŘW

Chuck Counselman wrote:

> 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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