[TowerTalk] Fwd: The Need for Grounding

[Edward McCann]

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It is unlikely Ohm's Law will ever be repealed,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 at 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 at 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 at 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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