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Re: [TowerTalk] [Bulk] Re: [Bulk] Antenna to Shack Ground Connection

To: towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: [Bulk] Antenna to Shack Ground Connection
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Tue, 03 Feb 2015 03:39:34 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 2/2/2015 11:22 PM, Grant Saviers wrote:
Thanks Jim, Mike and David for the data. 6 ga has plenty of strength and soils here are pretty benign, so I will go with it.

Be sure to check the local codes! Here, they do not issue, or inspect ham tower installations. No permits even if you ask for one as a CYA Some areas are quite strict.

73

Roger (K8RI)


Grant KZ1W


On 2/2/2015 7:54 PM, Jim Lux wrote:
On 2/2/15 9:30 AM, Grant Saviers wrote:
I'm considering what gage wire to use for grounding tower, ground rods
and Ufer guy anchors together, and need about 500' so cost is an issue.
The best pricing for solid bare copper I have found is $1.80/ft 2ga;
$0.85/ft 4ga; and $0.42/ft 6ga.

I suspect the code requirement for 2ga on 200/400a entry panels is to
handle the maximum interruption current of the affiliated main breaker.
The fusing currents for 2/4/6 awg copper are 72Ka/36Ka/28Ka respectively
which makes some sense.  (although with the usual 2 to 4 ohm rod to
ground connection, how can current ever get beyond a few hundred amps?
Not so if the ground is domestic water supply iron or copper.)

However, in the case of a lightning strike is fusing current important
since currents are likely an order of magnitude larger or more? My
historical examination of HV tower grounds often found big wire 2/0, 4/0
etc. so is that needed for a strike and it really doesn't matter much
between 2/4/6 ga, they fuse?  Or is the strike current so short that
fusing isn't a concern?  Then 6 ga would be ok to tie stuff together.

Is there some engineering basis for 2ga for ground rod and tower to
shack wiring?



Lightning is high peak, but low "action" (the averaged power dissipation, in units of amps^2*seconds) because it's a short pulse (50 microseconds)

Upshot is AWG 10 will handle a pretty large lightning discharge. (and lots of lightning rod grounds around the world are in that sort of size range.. a few mm in diameter)

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--

73

Roger (K8RI)


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