[TowerTalk] Lightning Protection

[jbwolf at comcast.net]

On 7/8/13 7:18 AM, john at kk9a.com wrote: 
>> I also have a shack on the 2nd floor and I also disconnect all cables 
>> going to the tower. I only use the station for major contests so doing 
>> this is not really inconvenient. Disconnecting however is not a reliable 
>> means of protection as the energy can be induced into anything nearby. I 
>> am not sure if there is any way to stop this from occurring. Even if you 
>> disconnect it is a good practice to have multiple lines of ground rods a 
>> single point ground and MOVs or GDTs on every rotator and relay. 
>> 
>> John KK9A 

>I'm not sure about the value of the multiple lines of ground rods *from 
>the entrance panel*.  I just don't see the physics of what it's doing 
>there.  The goal at an entrance panel is to have everything tied to one 
>reference voltage, and let that go up and down. 



But you don't want to "let" it go up  if you can help it.  The higher it goes up, the more potential for damage to the equipment.   One of the  goals of the entrance panel is  to help mitigate the rise of a stike at the panel.  

>For fast transients, the inductance of the wiring to the ground is going 
>to be dominant impedance, not the resistance to "earth". 



Which in turn causes the ground panel potential to rise even further.  Adding additional well engineered  " ground stake radials" connected to  the ground window lowers the impedance to get to ground.   For instance, consider five separate, one ground rod connections   to the window compared to one connection with five adequately spaced ground rods.  The latter will be much less effective. 


Jim, KR9U 


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End of TowerTalk Digest, Vol 127, Issue 17 
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