[TowerTalk] The Need for Grounding

[Roger (K8RI) on TT]

Inductance and magnetism.
Lightening is not a single event, but at its simplest, it is a series of 
pulses alternating between going up and going down with relatively steep 
rise and fall time.
Remember, Lightening is not a single DC event, LIGHTENING IS AN "RF" 
EVENT with the average stroke peaking "IIRC" around 1 MHz and tapering 
off above and below that point.
The rapidly rising current in any conductor produces a rapidly 
increasing magnetic field. This magnetic field builds a voltage of the 
opposite polarity (reverse EMF), often reaching a point, where the 
easiest path is no loner through that conductor. So, the lightening 
leaves that conductor for an easier path.  I've seen commercial towers 
struck, where the lightening would jump to grounded guys and jump from 
the guys across a rather large gap to ground rather than following the 
already grounded guy.  Hence the reason for multiple (earth) grounds.  
The lightening stroke will divide itself between many possible paths. 
Some will carry a lot of some of them, little, with the corresponding 
voltages

Spend some time on Google, or other search engines reading about 
lightening, what it is and how it works.  Moving, opposing charges in 
clouds and on the earth.  Charges move around in the clouds and on the 
earth. "Ground" is not just "Ground", or a single potential.  It's an 
interesting subject. Depending on your background in math and 
electronics, you can spend many hours just studying, lightening!

Follow some of the links provided by Jim Brown K9YC

73

Roger (K8RI)

On 1/13/2016 Wednesday 7:42 PM, W3YY 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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-- 

73

Roger (K8RI)


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