Did Lightning Rods do any Good?

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wrote:

When you hear lighning interference on the radio, is it just a SNAP - which would be all you get with straight DC?? No, it is a crackle/fizz typical of an alternating current of high rate of rise/decay ( I forget the term - something like dldt but that's not it)
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I understand. But remember that *if* you take 17 strands of a small diameter wire, combine them into a bundle, near DC the overall cable will act like 17 wires in parallel and have lowered impedance, but at high frequency the new bundle of 17 wires will not act like 17 wires in parallel, but rather act much like a large diameter, somewhat solid cable.
The only way to connect two points with a really low impedance is to make the connection WIDER than LONG. Then you have a shot at lowered impedance. And, that even means making the connection wider than you think necessary, like 2X wider. Then your connection becomes very low impedance acting much like a ground plane, very low impedance. Else, if connection is longer than wide, you have an inductor. And as you know, for an inductor it will not pass any appreciable current for a short bit of time, no matter how large a voltage you slap across it.
You can kind of cheat a bit and approximate a wide connection by using several connectors. That is why a well bonded wire grid structure protects buildings/structures so well. The connections, albeit not solid over the whole width, help lower the impedance of the connection by making it wider than long.
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The only way to have a bunch of conductors bundled, is to insulate each to prevent interaction. Except it must withstand, how many volts !!!! Even insulated, stranding close to other strands will have interaction nullifying what your trying to do.
The cables I have seen on buildings are stranded aluminum at least 3/4 inch in diameter.
Greg
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On Fri, 25 Jan 2013 16:28:56 -0800 (PST), Robert Macy

And if you make the conductor too wide, the capacitance to ground also increases - affecting the impedence.

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On Jan 26, 3:14 pm, snipped-for-privacy@snyder.on.ca wrote:

EXACTLY! Lowering the impedance further.
The currents flowing in a ground plane even at DC are interesting but for a transient become even more interesting. There are currents flowing in what you would consider the 'wrong' direction. Adjacent to the currents flowing in the 'correct' direction. As you may know a current in one direction [the main current flow] having currents next to it flowing in the 'wrong' direction [one enhances this effect by making the connection much wider than what seems necessary] cancels magnetic fields and really lowers the impdeance that the main current was 'seeing'. For exmple, consider the impedance between 2 points one inch apart in the center of a ground plane that is first only 1.5 by 1.5 inches, then compare to impedance between the two points when the ground plane extends out further to 4 by 4. Map the currents flowing. Very educational.
The allegory I mentally use to envision a discharge and makes it easy [easier] to understand lightning discharge is envision a rubber sheet. That is ground. Then pinch a small bit and lift up. that is like a lightning strike at the point where you pinched the sheet to llift it. It is easy to see that with uniform impedance around [the rubber sheet] the slope of the fields created by that discharge. You have like a teepee. And, you can see how there is very little voltage difference between adjacent points. Also, see why four legged animals are more likely to die than two legged animals from an adjacent strike. Now violate the uniform impedance of the rubber sheet by running conductors around. Unless those conductors are concentrically placed around the hit they will transfer high voltage gradients unintentionally between two points of widely varying voltage and since high voltages occur across very narrow regions SECONDARY discharges will occur.
A bit clumsy allegory but helps sometimes to envision the voltage gradient aspects of lightning.
Also, from experience of discharges in air. It is very difficult to get a super fast rise time of a discharge against a 'point' surface. A broad flat surface makes a blast discharge for the same amount of charge build up that a pointy surface produces. Thus, IMHO lightning rods can be made to work as protection and can be much better than nothing there at all.
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You're wasting your time... Go get a girl friend..
The predominant posters on this website do no recognize your expertise as being meaningful...
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On 1/24/2013 8:50 PM, Red wrote:

I agree with Robert Macy.
I believe hams like flat braid (like a flat stranded wire) for conductors that may carry high lighting currents.

Far as I know, the current design technique is to roll a sphere with a radius of 30m over the building and surroundings. The sphere stays on top of the rods. If the sphere touches the building, lightning can strike there.
You likely need fewer rods with the sphere design than the cone design. But if you transport the Empire State building to the middle of Nebraska, with no surrounding buildings, lightning can hit the side of the building. Sides of buildings may also need lighting protection.
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On Jan 23, 5:54 am, snipped-for-privacy@home.com wrote:

OK guys, this issue was discussed pretty thoroughly. Now it's time to see some lightning protection installed in a good location and good manor. <grin>
www.liveleak.com/e/07b_1284580365
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