[TowerTalk] Shack to service entrance ground

[Jim W7RY]

#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 <mph at sportscliche.com>
>> To: k8zm at oh.rr.com, towertalk at contesting.com
>> Subject: Re: [TowerTalk] Shack to service entrance ground
>>
>>
>> <According the the ARRL Grounding and Bonding book, Good Practices and
>> <Guidelines:
>>
>> <"Should I bond my tower to the station ground?
>>
>> <...Once the distance (between tower and station) exceeds 40 to 50 feet,
>> <however, the inductance of the ground conductor will be too high for 
>> the
>> <bond to be effective."
>>
>> <Mike WB2FKO
>>
>> 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