The important thing to remember is electricity doesn’t follow the shortest path
somewhere, it follows the path of least resistance. And it’s important to point
out that during a lightning event, that path is going to change, as the
lightning charge will easily overload a single rod, driving that rod’s
resistance sky high. Since the event is not yet over, the remaining charge will
follow the next-best path, which could be through your radio. Better it be
through the other rods in your network, no?
Is it useful to envision ground rods as resistors, and a chain of ground rods
as resistors in parallel?
Since we all know parallel resistors divide current among them, and as a group
present a resistance that is some fraction of their individual values, is it a
good meme to remind us of the importance of multiple rods?
73, kelly
ve4xt
> On Jan 14, 2016, at 10:35 AM, Edward McCann via TowerTalk
> <towertalk@contesting.com> wrote:
>
> On point.
> It is unlikely Ohm's Law will ever be repealed,
> by the current crew in the beltway or that if the pretenders to the throne.
> AG6CX
>
> Sent from my iPhone
>
>> On Jan 14, 2016, at 8:22 AM, Hans Hammarquist via TowerTalk
>> <towertalk@contesting.com> wrote:
>>
>> It's simply Ohm's law that still is valid. Yes, voltage across all the
>> inductance adds in too.
>>
>>
>> In my case, my tower is grounded with a resistance to ground of about 3 ohms
>> (when it was tested some time ago). If the tower is hit, (I guess) the
>> current is about 3 kA with a resulting 9 kV between the tower and ground.
>> Even if my shack is 300 feet from the tower (which it isn't in my case) you
>> will still have about 9 kV between your grounded shack and all the incoming
>> wires from the tower. (You might have 1 ohm resistance total in your cable,
>> but if there is no significant current the voltage drop is nill.)
>>
>>
>> If yo shack is grounded with, say, 6 ohms ground resistance you will still
>> have about 6 kV to ground. You will have about 1 kA going through your
>> cables. Now, if you have all your equipment well grounded in the same point
>> as the shack all the equipment will also be on the 6 kV potential, maybe a
>> little off as you might see the voltage drop due to variations in the
>> grounding point. Say that difference is 0.1 ohm. You will the see about 100
>> V which most equipment will tolerate.
>>
>>
>> Am I on the wrong thinking path? Correct me if I'm wrong.
>>
>>
>> Hans - N2JFS
>>
>>
>>
>>
>>
>>
>> Jan 13, 2016 07:45:50 PM, w3yy@cox.net wrote:
>>
>> The latest posts about grounding, and finally some free time here, prompt me
>> to ask the following question.
>>
>> Given lightning's desire to find the quickest way to ground, why doesn't it
>> expend itself in a single 8ft ground rod at the base of a tower, rather than
>> passing through another 250ft of transmission and control lines (also buried
>> in the ground) leading to the shack? I would think that by then it has had
>> plenty of opportunity to arc to ground itself.
>>
>> I am not disagreeing with the experts on this subject, but I just don't
>> fully understand what is commonly recommended. With only a single 8ft
>> ground rod at the base of my 100ft and 120ft towers which are about 100ft
>> and 250ft from my house, I have only suffered two minor damages from a
>> lightning strike in over 40 years. And, I'm not sure that even had anything
>> do with the towers, but was just an unrelated power line surge.
>>
>> 73, Bob - W3YY
>>
>>
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of EZ
>> Rhino
>> Sent: Wednesday, January 13, 2016 6:05 PM
>> To: Towertalk Reflector
>> Subject: Re: [TowerTalk] Grounds, 'remote' towers, 'house' power system
>>
>> I'm not in disagreement with you Jim, but then why doesn't NEC specify to do
>> things for lightning protection such as commonly followed by nearly all
>> commercial tower installations? Such as multiple ground rods, flat strap,
>> star grounds, etc? (Think Polyphaser's docs). We know that one ground rod
>> is woefully inadequate for a direct hit. If NEC is all about lightning, why
>> doesn't is specify using more than one? It sure seems like NEC is about the
>> bare minimum for AC protection and when it comes to RF and towers, it
>> doesn't really give much pertinent info at all.
>>
>> Chris
>> KF7P
>>
>>
>>
>>
>>
>>
>> On Jan 13, 2016, at 15:49 , Jim Brown wrote:
>>
>> On Wed,1/13/2016 2:35 PM, N3AE wrote:
>>> The NEC is focused on electrical safety and not necessarily the most
>> effective system for lightning protection.
>>
>> This is NOT true. The bonding required between your tower and power system
>> sub-panel is for LIGHTNING protection.
>>
>> In general, proper bonding is critical for lightning protection, electrical
>> safety, fire safety, and to minimize hum, buzz, and RFI. Proper bonding is
>> described in
>>
>> http://k9yc.com/GroundingAndAudio.pdf
>>
>> I'm not going to repeat it here for those too lazy to study it.
>>
>> BTW -- I TAUGHT courses on Power and Grounding for about ten years.
>>
>> 73, Jim K9YC
>> _______________________________________________
>>
>>
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