[TowerTalk] Re: Grounding and Lighning Protection

Sat May 1 15:28:06 EDT 2004

Disclaimer: My company manufactures "chemical" ground rods.

In decomposed granite it may be difficult to get good compaction around a
driven ground rods. Many people have used chemical ground rods in areas with
decomposed granite or difficult soil conditions with great success. These
rods generally include a clay based backfill material that addresses the
soil compaction/contact issue. Additionally they also introduce into the
surrounding soil electrolytic compounds that enhance conductivity.
Additionally chemical ground rods offer much greater surface area and offers
much lower impedance to higher frequency disturbances.

Regarding DAS, there seems to be an ongoing debate within the lightning
protection industry as to its effectiveness. But one thing that everyone has
agreed upon is that regardless of the type of lightning system (DAS,
Franklin, Early Streamers etc.) used, everything must be built upon a good
grounding system to work properly.

Will Sheh
www.atitec.com

on 5/1/04 9:19 AM, Grillo's at ah3c at frii.com wrote:

> Has anyone used chem-rod?
> http://theprotectionsource.com/CRods/crods.html
> 
> I'm thinking of this approach for my docomposed granite mountaintop site.
> In listing types of soils, their calculations would indicate my ground
> resistance would be around 300 ohms.  To bring it down to 5 ohms would
> require 4 of these rods and the chemicals to support it.
> 
> I am also looking at DAS.  My tower will be like a beacon as the highest
> point in the local area.  See below.
> http://www.lightningeliminators.com
> 
> Pete
> W0RTT
> ----- Original Message -----
> From: "Jim Lux" <jimlux at earthlink.net>
> To: "William Sheh" <wsheh at atitec.com>; <towertalk at contesting.com>
> Sent: Saturday, May 01, 2004 9:55 AM
> Subject: Re: [TowerTalk] Ground system
> 
> 
>> 
>> ----- Original Message -----
>> From: "William Sheh" <wsheh at atitec.com>
>> To: <jimlux at earthlink.net>; <towertalk at contesting.com>
>> Sent: Friday, April 30, 2004 6:28 PM
>> Subject: Re: [TowerTalk] Ground system
>> 
>> 
>>> I've been reading with interest what fellow members have been posting
>>> regarding the depth and orientation of ground rods.
>>> 
>>> One must keep in mind that there are many different types of grounding
>>> systems and that an effective grounding system consists of more than
> just
>>> burying ground rods in the soil. The key factor to keep in mind is what
>> one
>>> is trying to protect against. Is it direct lightning strikes, induced
>>> transient voltages/currents, side flashes or signal noise etc? Each type
>> of
>>> problem has its specific characteristics and strategies.
>> 
>> I fully agree.
>> Separate the RF grounding problem from the electrical safety grounding
>> problem from the lightning dissipation grounding problem, and separate
>> direct strike on your equipment from a) transients  conducted from outside
>> (i.e. coming from the power line) and b) potentials induced by a nearby
>> strike.
>> 
>>> 
>>> A horizontal conductor at a shallow depth (i.e. less than 3 feet) is
>>> perfectly allowed under the NEC and may be sufficient for electrical
>> safety
>>> of normal household circuits, but it is definitely not suitable for a
>> direct
>>> lightning strike. Under high current loads (a few KA) a horizontal rod
> can
>>> easily "jump" out of just a few feet of shallow soil coverage. A
> vertical
>>> rod is better restrained in the soil. Current magnitude under fault
>> dictates
>>> how much electro-mechanical energy is created. This is often an
> overlooked
>>> aspect in designing a grounding system.
>> 
>> I believe that the IEEE recommendation is at variance with your opinion.
>> They are specifically talking about grounding for lightning in the pages I
>> was citing. Indeed, the electromagnetic forces would need to be addressed,
>> and are, in things like substation bus bars (for that matter the forces
> from
>> just the normal kA load currents have to be dealt with). However, in the
> bus
>> bar case, the magnetic fields are much stronger than the earth's field,
> and
>> they're continuously vibrating (leading to fatigue failures, even with
> small
>> amplitude, on materials such as Aluminum).
>> 
>> On the other hand, one would think that in the extensive literature cited
> in
>> and forming the basis for the IEEE recommendation, such an event as rods
>> jumping out of the ground would have been mentioned as significant.
>> 
>> They do address the problem referred to as "smoking rods": boiling the
> water
>> in the soil due to the fault current.
>> 
>> As a practical matter, in soil of even poor conductivity, the current
> comes
>> out of the rod and into the soil pretty quickly, both from induction and
>> conduction.
>> 
>> Consider also... using the standard formula F=B*I*L (B=magnetic field
>> (Tesla, I= Current (Amps), L=Length(Meters), F=Force (Newtons)) Assume you
>> have a current of 10kA.  In a field of 1 Gauss (1e-4 Tesla) you'll have a
>> force of 1 Newton per meter.  The Earth's magnetic field is about 1/2
> Gauss.
>> 4.5N=1 lbf. That's only a few ounces.  Hardly enough to make the wire jump
>> out of the ground, although sufficient to make a conductor hanging in air
>> move around.
>> 
>>>> 
>>> Here are some references for those who are interested.
>>> IEEE Std 80-2000, Substation Grounding
>>> IEEE Std 142-1991, Grounding of commercial power systems
>>> IEEE Std 1100-1991, Grounding of Sensitive Electronics
>>> Mil Hnbk. 419-A, Grounding Protection
>>> NFPA 780, Lightning Protection
>>> UL Std 96A, Lightning Protection
>>> UL Std 1449, Transient Voltage Surge Suppression
>>> 
>> 
>> _______________________________________________
>> 
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> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
>> 
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