I can't resist chipping in with my experience at the other end of the
"protection" spectrum.
I put up a 100 foot commercial tower (200 lb 20 foot sections) about 40
years ago. Guyed with heavy duty power company galvanized strand and power
company egg insulators, broken into non-resonant lengths, first guyed at
30-60-90, now 30-70-90 to allow clearance for TH-6 @ 45 feet on a side
gate.
Out of a combination of ignorance and naivete I just used several good
ground rods (2x6' and 2x8') at the tower and one 8' outside the shack
window. Not a thing done to the house systems. Equipment each "grounded" to
a heavy wire, to a strap to the "station" ground rod. I may be courting
disaster, but I've never had a problem. Fourty years ago, but no longer as
much, the tower was 30-40 feet above the trees and heavy lightning storms
have come down my street on numerous occasions. I see two possible
mitigating factors. All coax and control lines are burrued at least 6" for
about 200 feet from the tower to the house. Also, I theorize that the
combination of antennas and guywires are effectively creating a "point
discharge" protection system. Point discharge protection seems to have
escaped discussion.
I'm sure we we all know of cases of severe damage by lightning. I feel very
lucky to have escaped, but based on 40 years of good luck I'm hesitant to
change anything.
Gene / W2LU
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "Tower Talk List" <towertalk@contesting.com>
Sent: Wednesday, August 04, 2010 3:21 PM
Subject: Re: [TowerTalk] A different question (I think) on SPG
> On Wed, 4 Aug 2010 10:48:59 -0700, Dick Dievendorff wrote:
>
>>I (will) have a main panel on the garage wall. The power company ground
>>rod
>>is right there. It's not much of a ground rod.
>
> That's a good reason to improve on it by adding more, separated by the
> distance equal to the length of the rod.
>>
>>There's a sub panel up in the radio room over the garage. That sub panel
>>is
>>connected to the main panel with four wires, 2 black and one white neutral
>>for 220, and a separate green ground wire. Neutral is attached to the
>>green
>>ground wire only at the main panel.
>
> Very good.
>
>>The radio equipment will be connected to one heavy conductor (a copper or
>>aluminum bar) within the shack.
>
>>The tower is a bit more than 100 feet away. It has several ground rods.
>>If
>>lightning hits, the tower and its antennas are the most likely first
>>victims.
>
>>I'm planning to put some PolyPhaser lightning arrestors inline to the
>>antenna coax, and through that effort the coax shield will be bonded to
>>the
>>tower's ground system.
>
> As K1TTT noted a few weeks ago, those arrestors should be very close to
> the
> protected equipment. Good practice is to a beefy conductive ground panel
> (copper or other good conductor) where they enter the building next to the
> gear, with that panel well bonded to ground.
>
>>Are you advocating a separate wire 100+' heavy copper wire to connect the
>>tower's ground system to the power company ground rod outside the garage?
>
> No. I would treat the tower as a separate location. Bonding as noted
> previously. At the AT&T site, the tower was right next to the building,
> and
> their budget was infinite. That proximity demanded that the tower be
> bonded to
> the building, and the budget allowed them to do it VERY well. :) In
> addition,
> they designed the building, the layout of the building and the tower, and
> the
> grounding arrangement before they started digging holes in the ground.
> When
> you do it that way, it's a LOT easier to do it very well, and with fewer
> compromises.
>
>>Is this "single point ground"? Looks like multiple paths to ground to me.
>
> Again, you are getting hung up on the words single point ground, which are
> confusing and lead to fuzzy thinking.
>
>>Is there a reason to run a separate wire from the shack ground plate to
>>the
>>power company ground rod, or would it suffice to connect it to the green
>>wire inside the sub panel, which has a green wire to the main panel and
>>then
>>to the power company ground rod. Isn't that more "single point" than a
>>separate parallel ground line?
>
> Please take the words "single point ground" out of your vocabulary. It is
> confusing things. Go back and read what I've written a half dozen times
> before. :) All ground electrodes associated with your house/shack MUST be
> tied
> together by the shortest practical path. That's power, shack, telco, CATV,
> building steel if there is any, metallic plumbing if there is any. All the
> gear in your shack should be bonded together by short fat copper. One big
> conductor, or more big conductors in parallel to lower the impedance,
> should
> take a junction of those shack bonds to the nearest junction of the earth
> electode bonds. All of the gear in your shack must also be bonded to the
> green
> wire at the local power outlet(s).
>
> Don't lose sight of the fundamental reason for all of this, which is to
> minimize the DIFFERENCE IN POTENTIAL between equipment that is
> interconnected,
> to prevent current from flowing THROUGH equipment, and to direct it away
> from
> equipment.
>
> Another point. The more things are spread out, the more difficult it is to
> minimize the potential difference between them. That's because connecting
> wires have inductance, and the current from a strike will induce voltage
> and
> current on them. To maximize lightning safety we want to minimize that
> distance. The safest layout from a lightning protection point of view
> would
> have power entry, telco, CATV, and the ham shack all right next to each
> other.
> Few of us have the luxury of that kind of layout, so we must make the best
> of
> what we have, or what we can do at reasonable cost (including the cost of
> keeping the XYL happy).
>
> 73, Jim K9YC
>
>
> _______________________________________________
>
>
>
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