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

[Roger (K8RI) on TT]

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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