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?
73,
Grant KZ1W
On 2/2/2015 3:17 AM, Jim Thomson wrote:
Date: Sun, 1 Feb 2015 20:44:30 -0500
From: Hans Hammarquist via TowerTalk <towertalk@contesting.com>
To: towertalk@contesting.com
Subject: [TowerTalk] Antenna to Shack Ground Connection
## The braid wont handle the current......so u still require 2 ga bare,
stranded copper wire between base of tower and shacks spg. The 2 ga
stranded, bare wire is buried in the dirt aprx 1-3 feet.
Then its in direct contact with the dirt. Even if the braid of coax used, the coax
would still have to be bonded to both top and bottom of the tower. It still
wouldn’t work, since the braid is covered
with insulation..and not in contact with the soil. Around here, the electrical
inspector will go crazy if you don’t install the bare, stranded, min 2 ga
copper wire between base of tower and shacks spg.
Jim VE7RF
Brian,
Yes, you are right all the shield of the feed-lines are connected (or should be
connected) tween the tower and the shack ground. The risk of getting the
shields fused (burned off) is reduced with a separate grounding wire between
the tower and the shack. Large enough your shack might even survive a direct
hit.
Again, the ground wire should be run close to the feed lines in order to
minimize induced current from near strikes.
Hans - N2JFS
-----Original Message-----
From: Brian Carling <bcarling@cfl.rr.com>
To: Bill Turner <dezrat@outlook.com>
Cc: Towertalk <towertalk@contesting.com>
Sent: Fri, Jan 30, 2015 11:10 pm
Subject: Re: [TowerTalk] Fwd: Antenna to Shack Ground Connection
Most of us have that already in the form of out coax feedline's outer conductor.
Typically this is grounded at the antenna and also in the shack. Am I right?
Best regards - Brian Carling
AF4K Crystals Co.
117 Sterling Pine St.
Sanford, FL 32773
Tel: +USA 321-262-5471
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