[TowerTalk] Fwd: A different question (I think) on SPG

[hanslg at aol.com]

 Gene,

"Don't call the d-l". I purchased a house 1997. The house was >200 years old. Speaking to the insurance agent it was pointed out that the building had no lightning protection but as "the house wasn't hit for more than 200 years it was probably OK. The house was hit 1 year and two days later and burnt down to ground. So much for "it never happend before" statement.

The new house has a protection system consisting of 3/4" copper pipes surrounding the house like a Faraday cage. I know I have had two direct hits with only minor damages (blown out surge protectors).

The idea with lightning protection is that, when lightning hits everything you want to protect are at the same (or close to) voltage potential as the current from the lightning passes by.

73 de,

Hans - N2JFS

 


 

-----Original Message-----
From: Gene Fuller <w2lu at rochester.rr.com>
To: Jim Brown <jim at audiosystemsgroup.com>; Tower Talk List <towertalk at contesting.com>
Sent: Wed, Aug 4, 2010 4:16 pm
Subject: Re: [TowerTalk] A different question (I think) on SPG


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 at audiosystemsgroup.com>

To: "Tower Talk List" <towertalk at 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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