[TowerTalk] Shack to service entrance ground

[Alan Swinger]

My tower l.egs have grd connections to an 8 ft grd rod using DXEs clamps - two have 50 ftr #4 wire radials w/ two 8  ft grd rods spaced 16 ft apart. The third leg connects to the shack using 3 in copper strap - ~ 150 ft - w/ an 8 ft grd rod every 16 ft along the length, The shack end connects to a grd rod and more 3 in strap which goes thru the shack wall and connects to the single grd plate, the house electric grd and all equipment. All cables have lightning shunts. 
Good luck - Alan K9MBQ
-----Original Message-----
From: <jimw7ry at gmail.com>
Sent: Aug 19, 2023 9:12 PM
To: <towertalk at contesting.com>
Subject: Re: [TowerTalk] Shack to service entrance ground

#2 AWG *solid* tinned wire is what is used for proper grounding (earthing) and bonding.

You will find very few molds for #2 AWD *stranded is a different* OD than solid.

Jim W7RY



On 8/19/2023 11:28 AM, Lux, Jim wrote:
> On 8/19/23 9:12 AM, jim.thom jim.thom at telus.net wrote:
>> Date: Sat, 19 Aug 2023 10:35:30 -0400
>> From: Mike H
>> To: k8zm at oh.rr.com, towertalk at contesting.com
>> Subject: Re: [TowerTalk] Shack to service entrance ground
>>
>>
>> > >
>> >
>> > > the
>> >
>> >
>> The tower is gonna ultimately be bonded to the station grnd >> anyway..... via
>> the braid of the coax.
>>
>> IMO,  bond the braid of the coax at the top of the tower, and again >> at the
>> bottom of the tower, then at the SPG.
>>
>> Then run BARE,  buried 2 ga CU stranded cable, from tower grnd setup to
>> SPG.  I used 2 ga cu stranded RW-90 power cable from each tower leg...to
>> it's own  8' rod...and cadwelded at the grnd rod.
>
>
> Burying 50-100 ft of bare #2 is like driving a bunch of ground rods, > it's a fairly effective grounding electrode in its own right.
>
> But it's unclear what the physics of needing #2 is:
>
> 1) Even a big lightning discharge isn't carrying enough "action" > (integrated current squared * time) to come close to melting #10, much > less #2. and if it's buried even less so.
>
> 2) As just pointed out, the inductance of 100 ft (30 meters) is 30 > microhenries - with a 1 microsecond rise time lightning impulse the > voltage drop is huge. So huge, it's essentially an open circuit.
>
> V = L di/dt = 30E-6 * 20E3/1E-6 = 600 kV for a 20kA stroke current.
>
>
> 3) If you were concerned about line voltage/frequency faults - I would > assume there's overcurrent protection at WAY lower than #2 sorts of > ampacity.
>
> 4) If you're concerned about "power line falling and shorting to > antenna"  now you're in a potential "high current, low frequency" > scenario.
>
>
> I suspect the popularity of AWG #2 for these kinds of applications is > a)in commercial practice you've got a big spool of wire on the truck, > and you tend to use the same thing for everything; b) AWG #2 is > mechanically rugged. That's almost certainly the case for a doc like > R56 or the FAA doc - They're providing a spec to contractors that is > "bullet proof" but "buildable and biddable" - They're not as cost > sensitive about the cost of the copper, for instance, since the labor > costs will dominate.
>
> And then once everyone uses AWG 2, things like cad-weld forms, clamps, > etc, all tend to be made for that size.
>
>
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--
Thanks and 73, Jim W7RY
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