Lightning Rod Ground Wire

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  #1  
Old 03-15-07, 04:22 PM
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Lightning Rod Ground Wire

I'm building a new house and need to install some lightning rods. Everything I found on the net shows the ground wire from the lightning rods to the grounding rods on the outside of the house. Is there any reason why I shouldn't place the wire on the inside of my house and then back out. I really don't want to see an ugly grounding wire running down the side of my house. I assume most people do it that way because they add it after the house is built.

I'm installing a zinc coated aluminum roof. To be safe I'm going to install aluminum lightning rods to avoid any copper aluminum corrosion. I will run an aluminum wire into the attic and down the inside framing of one of my exterior walls. Then I will use an approved aluminum copper connector and poke the copper wire out near grade level to a copper grounding rod. Does anyone see any problems with this design. I don't want the grounding wire to overheat and start a fire in the case of a strike.

Mark

Mark
 
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Old 03-15-07, 05:17 PM
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In my STRONG opinion a lightening rod system is WAY out of the realm of DIY work. You can do way more harm than good if you mess it up.

I do know the system must be bonded to the electrical GES but the rods ARE NOT one in the same.
 
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Old 03-15-07, 05:34 PM
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I am currently working on a building that employs a lightning protection system.

There are some places where the conductor is inside the buiding.

Is it safe? Don;t know
will it heat up ans start a fire? Don;t know.
 
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Old 03-15-07, 07:32 PM
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Great spot for an engineer to jump in.

Don't know what driving trains has to do with this.. But some know quite a bit about this stuff. so stand by.
 
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Old 03-15-07, 09:19 PM
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A lightning rod is NOT used to provide a path for a lightning strike to get to the ground. If lightning strikes your house, the lightning rod and the wire used are useless. A lightning rod is used to prevent a lightning strike at your house.
 
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Old 03-16-07, 04:29 AM
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That's funny Bob. Everything I have read, or have been told, is completely contrary to that.
 
  #7  
Old 03-16-07, 08:04 AM
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Lightning rods and lightning protection systems are not a well-understood science, or if they are well-understood, not everyone has the same understanding. If you read 100 articles on them, you'll get 100 different points of view. I've read articles that say what Bob says, and I've read other articles that say what Speedy says. It's best I think if everybody goes and reads them themselves (google can help here). I don't think we're going to settle it in this forum.

It is my opinion that nothing can protect you against a powerful direct hit by lightning. But there are a lot of smaller electrical events during an electrical storm that are less dramatic than that.
 
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Old 03-16-07, 08:06 AM
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the insurance companies have a lot of data on this

Building height has a strong correlation with strike frequency, but there are instances of hits on low buildings in the shadow of very high towers, etc.

to the argument of ground rods and their effectiveness. It is true that lightning will find its way to ground with or without ground rods and lightning protection sytems (LPS). This should be real obvious to anyone that sees a tree take a lighning hit. LPS attempts to control the path of as much of the current as possible. There are ongoing debates on whether LPS can attract hits or prevent hits. Lets save that for another thread.
Back to the insurance industry. There is strong evidence that buildings with LPS do sustain less damage than those without LPS. The bonding and rods do help carry the current away from flammable material like wood, and damageable material like concrete. In that sense, the electrodes, wires, and rods absolutely do serve to protect life and property. The taller buildings require larger cable, due to the higher incidence of hits. Flashover and density of rods, downcables, and air terminals are other considerations.

Putting downcables in or on building construction material should not be a fire concern if connections are done properly. Smart installation provides some clearance to sensitive wiring, however, since strikes do cause very high EM disturbances in the vicinity.
 
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Old 03-16-07, 04:21 PM
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Bob, have you got any theory behind what you are saying?

I cannot imagine how an LPS would do anything to prevent a lightning strike. To me, the bigger unanswered question would be, does the use of one increase the likelyhood of a strike.

I have concerns that it would so I'm willing to help the neighbor pay for one for his house so hopefully it will attract the strike to his house and avoid mine. lol.

I believe that although we cannot truly control lightning, an LPS is an attempt to direct the strike away from actually entering and interacting with the building it is installed upon by providing a low impedance pathway to a ground source.
 
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Old 03-16-07, 04:38 PM
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From high school physics through college physics and electrical engineering classes, I have always and without exception been taught that a lightning rod is meant to prevent a lightning strike. I have never been taught that their purpose is to channel the energy safely to ground.

While I cannot do justice to what I was taught years ago, the theory is that path helps to equalize the charge difference, thus preventing the strike from happening, at least right there.

If you follow John's suggestion you will find a variety of documentation on the subject, as John has indicated. Indeed the literature is not quite clear on the subject, and there seems to be no consensus. Some writings support my position, other writings support the other position. However, just about every writing agrees that we do not completely understand the issue.

Bottom line. Everybody needs to do their own research and make their own decision. Finally, any installation needs to be done in the most currently approved safe manner.

One more point I will make, if a lightning rod does exist to channel the charge safely top ground, and if it will safely do so, I sure don't want that wire inside my house.
 
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Old 03-16-07, 04:43 PM
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Lightning rod systems were around long before electricity in homes was common. When a farmhouse was the only thing above 5' in height on the prairie, they saved the house. They worked well then, but I will not try to explain why, they just did.
 
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Old 03-16-07, 05:44 PM
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I don't know Bob. I looked at about 20 websites and none of them presented anything other than an LPS is intended to direct or guide a lightning strike and prevent it from becoming carried by the structure or any of it;s systems.

If you could point me to some of those sites that claim prevention, I surely would be appreciative.

as far as equalizing the charge; that is what the lightning strike is doing. It is removing the potential between the clouds and the ground. It will do it anytime the potential can overcome the insulative properties between the two points.
 
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Old 03-17-07, 12:04 PM
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I have a degree is physics and nuclear engineering and I'm no expert on lightning. And I'm guessing there are only a few people who are experts. Wikipedia has a few things about lightning rods

http://en.wikipedia.org/wiki/Lightning_rod

Basically storms are so dynamic and large that it is difficult to perform controlled experiments. I've heard both theories that rods prevent lightning and it channels lightning. I tend to belive it channels it more than prevents it. Unless there is a lot of upward movent of air the prevention theory doesn't seem to work. You have a rain cloud dumping rain by the thousands of gallons with each drop carry charge downward and your little lightning rod giving off a few electrons to the moisture in the air is going to prevent a strike in clouds hundreds of feet above it. The clouds are moving to fast to make a difference. It is also difficult to understand how a 14 gauge wire can safely care away kiloampres and a billion volts. Of course it is most likely because of the short duration of the strike and the bolt tends to branch. At any rate there are plenty of occurances of lightning striking rods and nothing occuring to the building and no way to prove that the rods are preventing strikes with current data.

Mark
 
  #14  
Old 03-17-07, 02:55 PM
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wires that carry lightning

I did read a old report that tried to find out how big wire had to be to successfully carry a lightning hit. There is evidence that #8 Al solid wire is not big enough, but #6 Cu is. Some old chuch in germany had its #8 wire fuse, apparently. Look at your utility poles. I think i see #6 Cu solid being used. Buildings per code use much larger,however.
 
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