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[TowerTalk] Re: [Antennas] Braid as an Effective Grounding Material

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Subject: [TowerTalk] Re: [Antennas] Braid as an Effective Grounding Material
From: (Mark Nelson)
Date: Thu, 6 Nov 1997 18:46:27 -0800
That's what is generally used at Broadcast Radio transmitting sites ...
(Copper strap, like 4-12" wide0 ... Cheers!
-----Original Message-----
From: kingpop <>
To: Roderick M. Fitz-Randolph <>
Cc: <>;
To: <>
Date: Thursday, November 06, 1997 3:31 PM
Subject: Re: [Antennas] Braid as an Effective Grounding Material

>The best thing I know and have never heard disputed is wide stripes of
>flashing available from roof supply stores  De  N4YFX   (Tim)
>Roderick M. Fitz-Randolph wrote:
>> >HI Rod...I've never thought braid was good for a ground, and now that
>> >I understand the mechanics (OK< the electromechanics) of the situation
>> >my gut feel was right.  You need the ground wire to conduct gobs of
>> >and it needs to be THICK because of skin effect.  Braid, even tinned,
>> >doesn't have near the effective thickness of good old solid copper wire.
>> >The energy in lightning (last measurements I saw from a research team in
>> >the late 70's) goes way up into the VHF region, but there's plenty of
>> >energy below that to sizzle your braid.
>> >
>> >Just to give you an nuclear stations they use copper BAR (abt
>> >1 in by 3 in as I remember) for grounding.
>> >
>> >No, no, not use braid for a ground.  You'll have plenty of
>> >say "I use it, and nothing happens."  I say:  "You haven't seen 'real'
>> >lightning yet."
>> I considered the braid because it has less inductance than copper.  My
>> particular situation here is not quite the same as for most situations in
>> that I have a 130 foot tower with a 20 foot mast (7 down and 13 up) and a
>> lightning rod that extends to 150 feet above the ground.  Each leg of the
>> Rohn 25G is connnected to two 8 foot lightning rods, 16 feet apart... for
>> total of 6 lightning rods.  The coax cable that connects the antennas to
>> ham shack is buried for 250 feet from the base of the tower to the
>> Some of the coax is 3/4" CATV aluminum shield cable that is buried direct
>> have acidic soil here so direct burial of CATV aluminum jacket coax is
>> acceptable).
>> Only a small amount of voltage has reached the ham shack during a
>> strike.  Two of the three strikes did not hurt the Alinco VHF
>> that remain connected to my PacketCluster node 24 hours a day.  I have
>> installed PolyPhaser IS-50US-C1 devices in both of those coax lines now
>> intended to run the 3/4" braid 6 feet (from the 1/8" thick aluminum plate
>> which the PolyPhaser devices are mounted) to ground rod system at the
>> wall of the hamshack (which is a different ground system than that of the
>> tower because of the distance involved and PolyPhaser's statement that if
>> the tower is more than 100-150 feet away from the hamshack, a common
>> ground is not necessary; rather two separate, but adequate grounding
>> should be used).
>> There are two prime concerns:  (1) The braid must have low enough DC
>> resistance to effectively short the current to ground and (2) the braid
>> (or whatever is used) must be of small enough inductance to assure that
>> L di/dt does not cause the sort of build up over its length that allows
>> a 100 foot well grounded tower (that has only 0.1 ohm DC resistance from
>> top to bottom) to achieve > 200,000 volts from top to bottom,
>> at the moment of the typical 18,000 Ampere strike.  The only two viable
>> choices are a copper strip 6" to 9" wide running from the common tie
>> at the station console to the grounding system 8 feet away (and through
>> wall via a 3" PVC) on the outside of the house.
>> Copper strip is out of the question (even though it exhibits much less
>> inductance than either a wire or braid) because of the small aperture of
>> PVC.  This leaves only large copper braid or tinned copper braid as a
>> choice.  Based on the excellent protection the 7 feet of 3/4" copper
>> afforded at the digipeater site at which every other piece of
>> communications equipment was destroyed, the electrical distrubution box
>> was blown to pieces, the repeater telephone line input box was nearly
>> vaporized, the ground lug on my power supply was almost arced in half,
>> yet my equipment protected by the 3/4" braid to two ground rods and the
>> PolyPhaser device inline with the coax, leaves me to the inescapable
>> conclusion that the small charge remaining at 250 feet from the
>> tower will be successfully "bled" or grounded by braid that is even more
>> massive than that which successfully protected the equipment from the
>> of a direct strike at the digipeater site.
>> My question is: Is the tinned copper braid to be avoided because of any
>> oxidation problems with the tin?.... i.e., should I only use large copper
>> braid as opposed to large tinned copper braid?  Does the tin on the
>> of the copper pose a problem in light of the well connected and Penetrox
>> protected joints at either end?
>> Comments gratefully accepted.
>> Rod, N5HV
>> ------
>> Submissions:

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