[TowerTalk] The Need for Grounding

Thu Jan 14 12:59:44 EST 2016

I will be using 4 elevated radials.  The ground screen is not attached 
to the
bottom of the vertical (in this case the tower) and is not part of the 
radials system.   It is to
help reduce near field  losses.

Bob
K6UJ

On 1/14/16 9:45 AM, David Robbins wrote:
> what is the intended purpose of said ground screen not being connected to the tower.  if you area going to shuntfeed the tower then you want the ground screen
> as big as you can make it and attached securely to the tower.
>
>
> Jan 14, 2016 10:25:22 AM, k6uj at pacbell.net wrote:
>
> Hi Roger,
>
> I am concerned now with my planned ground screen around the base of my
> tower.
> I am planning a shunt feed to the tower for 160.
> I will have separate elevated radials, 4 of them, at 14 feet above the
> ground.
> The ground screen will extend out 15 to 20 feet from the base of the
> tower in all directions
> and will not be attached to the tower. I am thinking of leaving a 1
> foot clearance from the tower
> to the ground screen. The rub is I am thinking of also connecting the
> ground screen to a nearby 15' x 70'
> parking slab welded wire mesh which is in the slab for reinforcement.
> This would give me more
> ground screen. Now I am thinking of the lighting possible arcing over
> to the ground screen and then
> possibly going out and cracking the concrete slab. Maybe I should leave
> more than 1 foot space from
> the ground screen and the base of the tower.......... Or forget about
> tying in to the 15 x 70 slab too ?
> BTW, I have 3, 10 foot ground rods attached to the tower.
>
> Bob
> K6UJ
>
>
> On 1/14/16 3:36 AM, Roger (K8RI) on TT wrote:
>> 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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