Lightning Questions

[bphgravity]

1. Nearly all resources I have read that describes the process of a typical lightning strike places the Earth (land) as an essential component. Streamers from grond-based objects connect to downward leaders from the sky. Yet at the time, it is estimated that up to 85% of the total lighnting strikes happen over water, namely the ocean and especially the Gulf of Mexico. If lightning is so intent on Earth (ground), why does it mostly strike non-land locations?

2. On the same note, I have read that it is estimated that 1 in every 5 aircraft flights are struck or effected by lightning. Again, no land or Earth involvement. Why is the NEC so positive that connecting the electrical system to Earth will assist in lightning protection?

3. Approx. $2 billion in loses to utilities in the US and over $1.7 billion in losses to homes from lighnting damage. As I recall, somewhere in the area of 300,000 claims are made a year to insurance companies from lightning damages. Do these figures indicate grounding of electrical systems are protecting against lightning? Do these figures indicate that all these occurances are because grounding was not adequate at these buildings and facilities?


Or, is this all evidence that it most likely does not make a bit of difference if your building and structure is effectively grounded as a matter of protection against lightning.

 

[ryan_618]

Re: Lightning Questions

I think it depends on what you are trying to protect. If you are trying to protect the structure from a direct strike...think again! You're house is going to be in flames, even if you have less than one Ohm.

I would be willing to bet that most of the insurance claims are people claiming their sensitive equipment has been damaged. Earth grounding will do nothing for this, only a propoerly installed TVSS will.

I think lighting strikes non land locations more than land because 2/3 of the world is non-land.

 

[catchtwentytwo]

Re: Lightning Questions

Even the experts seem to disagree on this subject. I subscribed to the B]Lightning Protection ? Lightning & Power Quality Issues newsgroup[/B] newsgroup and nothing seems as "cut & dry" concerning lighting protection. Check it out at http://groups.yahoo.com/group/LightningProtection/

 

[petersonra]

Re: Lightning Questions

1. Perhaps because most of the world's surface is ocean?

2. It may be that the metallic body of an aircraft tends to protect the inards of the aircraft from the effects of the discharge. Hard to have a potential difference on a big piece of conductive metal. Same as being inside a metal car during a lightning strike.

3. I suspect grounding reduces the potential for damage, and may in fact reduce whatever damage is done, but cannot eliminate any potential for damage.

As for your last question, suppose your electrical system is hit by lightning. Would it be preferable for it to be grounded or ungrounded? I think the answer is that if it hits the incoming power lines, it's more likely to connect to a grounded line and go to earth than to connect to a line that has a higher impedance to earth. And because your incoming power lines are typically conductive and up high, it may well divert at least some strikes away from your home.

<added>Might be a good reason to have an uninsulated service neutral coming in overhead.

[ May 15, 2005, 04:47 PM: Message edited by: petersonra ]

 

[pierre]

Re: Lightning Questions

Bryan
I am not a lightning expert, but have some knowledge.

1. As Ryan has stated, water covers most of the earth. Also I do not think they study the effects on water as much as earth, because we have not started building there... yet.

2. Connection to earth for building protection gives the lightning a path for dissipation, as lightning will dissipate in earth.

3. Without knowing the exact type of damage to buildings/homes, I would say that a lot of homes are not protected by lightning schemes. Also most homes that I know of that have been hit by lightning are usually hit on the roof or some other structural part other than the service, starting fires and creating a lot of damage- even death.

I do think that the protection schemes when installed properly do help to reduce the amount of damage to homes/buildings. Repeat-reduce the amount of damage.

 

[bphgravity]

Re: Lightning Questions

This is the point of my questions. Why do we state lightning discharges into the earth? Does this imply that if lighting does not hit the earth, it does not discharge? Hence my point that most lightning hits water and does not necessarily need earth as apart of the equation.

It seems more reasonable to me to state in the case of lightning that we are intending to bring earth charges to the sky verses lightning charges to the earth?

 

[ron]

Re: Lightning Questions

I think it is not so much bringing one type of charge from one place to the other, but to equalize charges at both places.

 

[charlie b]

Re: Lightning Questions

What makes you think that hitting ocean is different from hitting dirt, as seen from the perspective of a lightning bolt? My guess is that the resistance per cubic cubit is lower for sea water than it is for top soil.

Lightning is nature's way of restoring equality of charge. It results from an overabundance of electrons in the clouds and a shorage of electrons planet-side. When lightning strikes, the electrons it carries with it will find their way to new homes (i.e., to atoms that had been missing electons), even if they have to travel through ocean water to find those new homes.

 

[karl riley]

Re: Lightning Questions

It might be helpful to realize that a lightning discharge is just part of a circulation of electricity near the earth's surface. I don't see the lightning as disipating when it hits the earth or sea but moving to equalize the charge buildup. And as we know, many strikes are from earth to cloud. It is a circulation. Charge continually builds up and equalizes, over and over.

I once watched a storm from my porch in the Arizona desert. There would be a strike to earth. Then after a couple of minutes there would be a cloud-to-cloud strike from some distance to the area where the earth strike had occurred. This happened over and over. One place discharged and then received an equalizing charge from another part of the cloud layer. It became predictable.

Karl

 

[brian john]

Re: Lightning Questions

NOT AN EXPERT, BUT ALWAYS WILLING TO DISCUSS LIGHTNING

1. As Charlie stated the ocean is EARTH, we say lightning strikes Earth not necessarily land. Salt water is a very good conductor and lakes and rivers are proberly a close second.

2. There is also inter cloud lightning that strikes side ways and up. Any plane in the path may be struck. It is my understanding that the lightning travels around the plane, on it's path to earth or another cloud. Though there are cases where the plane's skin has been damaged as well as the electronics on board.


Lightning damage ranges minor house damage; shingles, siding, wiring fried, mirrors damaged (I've seen all this and more)to partial to complete burn down. Then there is the electronic damage as mentioned.

If your house is in a high strike area, located on a hill, should you install a lightning protection system, roll the dice. But I believe experience shows that a Franklin Rod system with associated down conductors and adequate ground ground?/ring minimizes damage And a properly installed system of TVSS's will minimize damage to electronic equipment.

We have a customer that has several sites one gets hit all the time and damage to the structure and equipment is minimal another similar site has only had two or threee lightning hits (that we know of) this second site has sustained damage twice. TVSS blew out and there was structural damage. Whats the difference? Maybe the peak voltage/current, duration, multiple strikes, at once,

 

[oceanaradio]

Re: Lightning Questions

Brian's comments about simlar structures, locations and protection, with differing results, are fortunately not typical.

Engineers today are trying to analyze the resonant frequencies that parts of structures and internal systems present to lightning. This is about as extreme as it gets, in the attempt to understand why lightning behaves in some mysterious ways.

It is much more typical though, for damage assessment to reveal rather simple errors or underestimations than to be left with big ? about why a strike did damage.

Regarding aircraft, every Spring the National Hurricane Center, in conjunction with NOAA, travels to select cities with one of the infamous "Hurricane Hunter" C-130 aircraft. Examine the fuselage on that aircraft sometime - literally dozens of patched holes where lightning has neglected to follow our design, which was to leave the aircraft via the many static discharge rods that line the aircraft. Those planes are struck hundreds of times, and yet rarely suffer any internal damage.

Those of us who are sailors as I am, may have spent dozens of days and nights in horrific thunderstorms, and wondered why lightning never struck an aluminum mast 65' above the water. The same storms may have dozens of close strikes that hit the water surface instead, and here was this tall mast all by itself, never struck.

The answer is, from two miles high, lightning is not impressed by a golpher, a sailboat mast, or a building. A general area of the earth is already going to be hit, influenced more by the wash of positively charged ions that preceed the storm, than any individual person or thing nearby. We can only plan for and either avoid or be ready to absorb, that which does choose to visit our place and point in time.

Jack
Virginia Beach, VA

 

[hurk27]

Re: Lightning Questions

By jack: Engineers today are trying to analyze the resonant frequencies that parts of structures and internal systems present to lightning.

I was trying to get the professors At FL.U. to accept this years ago. I was always perplexed as to why lightning would hit a 20' high tree and leave a 150' tower alone that was less than 40' from it. It was the communication courses That I took at Mid Florida Tech that opened my eyes to the fact that when a signal has a given resonating frequency that it can only resonate upon a likewise conductive structure that has the same given ability to resonate at that frequency. This is the fundamentals of how radio transmission and receiving works. and so if lightning has the AC fundamentals it would explain how it sometimes can see one contact point over another even when it would seem that the one should have a greater Chance of being the contact point.
We have to stop thinking in the form of DC resistance when it comes to lightning.