lightning rods any believers ?

[JB4310]

I don't know much about lightning protection but I occasionally find myself repairing components of lightning protection systems on old churches and schools, mostly because no one else wants to or can get to them.

This is a church I've worked on for close to 30 years now, the system is old and often I find wires broken so I splice them where possible. We work across the ridge of the building sometimes and believe me you don't want to sit on one of those 12" high spikes

Pictures;
This chimney is 92 feet high, you can see the old system in place, we use a boom lift, imagine how the old timers got up there!
Plus, Lightning truncated one of these twin steeple towers years ago, unsure whether it was protected or not, but guessing not.

Oh yeah don't forget it was Ben Franklin who gave us lightning protection, probably one of his greatest and most enduring contributions/ inventions, even though not many people even give it a second thought. It's pretty much a world wide standard that we could not live without.

JB.

 

[xtn]

There seem to be many here who believe lightning rods and their cables and grounds are meant to safely conduct the current from the lightning strike to the ground. This belief is not correct, but it is very common.

As many of you have said above, a lightning strike presents far too much current for any reasonable cable to handle.

Lightning protection systems are there to ground the structure and maintain it at the same potential as the surrounding landscape. In laymen's term, this sort of "flattens" the structure, reducing its electrical presence.

A good example - look at sailboats. Every single sailboat has its mast grounded to the vessel's bonding system, and the bonding system is 'connected' with the water. When sailboats do get hit, they generally lose all their electronics and they often have a hole blown through the hull where the bonding system is in contact with the water. The grounds can't conduct the lightning away. Instead, the grounds reduce the charge on the boat, keeping it at the same potential as the surrounding water, essentially "hiding" it instead of making it an attractor.

Certainly a good point, and modern building protection schemes do not incorporate a "rod" up on the roof. They are indeed designed to "hide" the structure as you state.

But the grounds do indeed help conduct the electricity away if there is a strike. Maybe the energy blows them out in the process, but the occupant of the boat was protected. If they don't conduct it, how does it get from the mast to the point of hull blowout?

 

[SPYDERLK]

Some people will believe anything. Lightning will strike where it wants to, Metal roof by a golf course, golfer out golfing, lightening strikes golfer, why. Do you really think you are directing the lightning to a specific area, or warding off lightning. Does the lighten strike up or down? How many metal roof buildings in the US? How many cars have been struck by lightning? They have rubber tires. Go figure. How come lightning strikes church steeples, metal or wood? That is the good lords house of worship. Why, Why Why

There doesn't seem to be any logic where lightning will strike.

Somebody in those pictures had a bad day.

Lightning rods seem to draw attention, like saying, pick me, pick me. l

I have been in aircraft struck by lightning. The plane just got in the path of the charge. It did knock out a few things, and burned holes in the radar housing.

The "logic" to all lightning strikes is that they take the path of least resistance. It may often be difficult to perceive that it has done this because general knowledge about electricity must be developed a bit further in order to have a chance at explaining the behavior of virtually instant transient events ... [arcs]. Electrical resistance is one thing, and electrical inductance is another. Together they define the Path of Least Resistance. Inductance impedes the progress of an event. The more sudden the potential event the more it is impeded by inductance. Events that by nature are "instant" are impeded almost infinitely by inductance - in other words the instant event cant happen if there is any significant inductance present. [That arc can blow thru a resistance, but nothing can blow thru an inductance.] -- So a lightning event often looks like it did not take PLR because it was forced to go around an area of high inductance not apparent to the observer. A critical look after the fact will see the telltale characteristics.

As for lightning rod "pick me", pls revisit post #16.
larry

 

[forgeblast]

I read the book The First American: The Life and Times of Benjamin Franklin, it talks about how he helped us out in France because he was known at "The man who tamed Lighting". very good book btw.

 

[Dargo]

Some people will believe anything. Lightning will strike where it wants to, Metal roof by a golf course, golfer out golfing, lightening strikes golfer, why. Do you really think you are directing the lightning to a specific area, or warding off lightning. Does the lighten strike up or down? How many metal roof buildings in the US? How many cars have been struck by lightning? They have rubber tires. Go figure. How come lightning strikes church steeples, metal or wood? That is the good lords house of worship. Why, Why Why

There doesn't seem to be any logic where lightning will strike.

Somebody in those pictures had a bad day.

Lightning rods seem to draw attention, like saying, pick me, pick me. l

I have been in aircraft struck by lightning. The plane just got in the path of the charge. It did knock out a few things, and burned holes in the radar housing. .

Here ya go JJ, this is a big strike (but poor quality picture - although verified authentic) christ the redeemer statue picture of lightning strike | Picture 15

About 8 or 9 years ago I had a wood handled shovel get hit by lightning while I was digging with it. It pretty well blew the spade part completly off. Me, I think I just lost a little hearing and, of all things, most of my eyebrows (but they grew back...with a vengence! )

 

[Bill Hoffman]

As the local atmosphere builds up a charge in a thunder storm, the ground builds up an opposite charge called a ground charge shadow. Lightning will strike when the potential difference between the two charges is strong enough to ionize a column in the air. A lightning rod works to bleed off the ground shadow from the pointed end of the lightning rod. Because the electrons at the end of the rod are repelled from each other they leave the point of the rod effectively reducing the potential difference between ground and atmosphere. Refer to the phenomenon of St. Elmo's fire seen in the rigging of ships, usually at the end of the masts and spars.

Or, see post # 16.

The charge bleed off can be easily demonstrated with the use of a Van de Graaf generator. Did it with my science students for years. Used a little house model. No rod, the house got hit. Put a sewing pin projecting from the roof, pin point highest, and the house NEVER got hit, the charge bled off the point of the pin. Every time.

Bill

 

[JB4310]

most of my eyebrows (but they grew back...with a vengence! )

:laughing::laughing:

I saw, after the fact where a stop sign got hit. there was nothing left of the sign, the fire dept was pouring water on the surrounding area for an hour and it was still steaming. This was in someones front yard and the entire surrounding 10-20 feet of yard was greenish brown glass!!

Not sure if that is a common occurrence or just a very powerful strike?

I had a spruce tree hit in my front yard. it exploded the tree half way down and left rough cut "lumber" strewn around my yard. My brother came over and asked why is there 2x6's all around my front yard. I didn't know the tree was hit til I went out there. This was in a row of 70 foot tall trees, the one thing different about this tree was there was a steel property pin in the ground right next to it.

JB.

 

[ducks13]

Lots of good and bad information here; the National Fire Protection Association writes a code, NFPA 780, that is generally viewed as the authority on lightning protection in the USA. There are a number of factors that are considered when deciding if a lightning protection system is recommended. They include the location/height of the building (tall or high on a hill is not good), the building material (wood is not good), the value of the building's contents, the frequency of lightning in that area of the country and a couple more I don't recall off the top of my head. Lots of wood house get hit by lighting and the fire department gets usually gets there in time to put it out before it is a total loss. A wood barn full of hay out in the country is probably not the best building to have without lightning protection. On most modern steel/concrete buildings you may get a hole in the roof or maybe blow a piece of concrete off but then the lightning strike is carried relatively safely to ground through the steel or concrete structure without causing severe damage.

Another item that hasn稚 been mentioned that some of you may find interesting is that on most power transmission lines the top wire or wires are lightning protection to keep lightning strikes off the power conductors (that 30 degree cone of protection idea again) and to give the lightning a safe path to ground. The top wire(s) are connected to a ground through the steel of the tower of with a copper or aluminum conductor in the case of wood supports.

Providing a safe path to ground is the basic principal that the Franklin system works on. I don稚 believe there are any building codes in the US that require lightning protection systems on any buildings with the possible exception of some local codes in area like central Florida where, as someone else mentioned, has a lot of lightning strikes. Lightning protections systems are required in some parts of Europe but I believe that is mostly the results of politics not science or a cost benefit analysis.

 

[Redbug]

Question for JB...Looking at your pictures, the second picture shows a church roof that is shingled. Looking closer at the shingles...I see a lot of raised areas on the shingles. What are they? Roofing nails that have popped up? Or something else?

Also, about lightning...you can have positive and negative strikes. That is, lightning can come from the sky down to the ground...or from the ground up. The more severe storms have more positive strikes...lightning going from the ground up to the cloud.

You can get ground rods that screw together. I have pounded down as many as four in one length to get a better ground, (in sandy soil). I have used an ohm meter to check how good the ground rod is making a ground.

 

[Egon]

Lightning

Information on lightning.:thumbsup: