Lightning protection

[steve66]

Someone else posted the following link in another thread:

NFPA Lightning protection

I have always regarded lightning protection (i.e. lightning rods) as maybe it works, and maybe it doesn't.

So my question is this: Do you think it is a scientific fact that lightning rods actually provide protection for a building or structure?

Steve

 

[charlie b]

Re: Lightning protection

Whether something is a "scientific fact" is a question of, well, fact. What I may think about the topic will not cause a fact to become non-fact, nor will it cause a non-fact to become fact. There's another of those (groan to follow) "Charlie-isms" (groan :roll: ) on that topic:

No degree of belief, not even the deepest of convictions, can create truth.

However, to answer what I believe to be the intent of the question, I will say that I possess no facts, and in the absence of facts I choose not to accept the proposal. I infer that you doubt the value of lightning rods. I doubt it too.

 

[bdarnell]

Re: Lightning protection

Originally posted by steve66:
Do you think it is a scientific fact that lightning rods actually provide protection for a building or structure?

We have had to install lightning protection systems on several buildings as a part of our contract in past projects. I spent some time with our vendor who tried to explain the "rolling ball" theory and how lightning protection works. After my eyes cleared from the glazed look, I came away with the belief that about the most that can be expected from a lightning protection system is for it to safely (with hope) conduct the strike to earth via the air terminals and down conductors. I certainly have no belief that a lightning protection system will keep lightning from striking a structure. Lightning pretty much does what it wants.

 

[steve66]

Re: Lightning protection

Fair enough. Maybe I should of phrased the question different.

How many people are currently specifying lightning protection systems (other than surge arrestors) for projects?

I have never specified lightning rods before, but I am starting to think about changing that. From the link, NFPA seems to think they have some merit. Also, if the Florida building codes are actually requiring them, that seems to give lightning rods some credibility.

Steve

 

[bwyllie]

Re: Lightning protection

From what I understand about the lightning protection, the system is installed to actually attract the hit away from the building and into the lightning protection system which will transfer the strike to ground. If you had no protection system and the building was struck there is a potential for damage to the electrical system which leads to downtime for tenants which leads to headache$ for the bldg owner.
In evaluating the lightning protection system one should consider (1) the occupancy of the building and what any electrical downtime would cost to the tenants (2) height of the building (3) height of surrounding buildings (4) the amount of lightning strikes in the region/area.
Some insurance agencies will give a discount to buildings with a UL Master labelled system installed. When the budget is a concern most of the time the lightning protection system is the first VE item.

 

[sandsnow]

Re: Lightning protection

I like Charlie-isms

Keep 'em coming

 

[bob]

Re: Lightning protection

Lightning rods and down leads do not prevent a building from being hit by lightning. They do provide a better path to ground as opposed to the building structure. If the system in installed properly, there is little chance that the structure will sustain damage.

 

[bphgravity]

Re: Lightning protection

The problem with an LPS is that you can never say for sure if it is actually doing its job or if it ever has.

The problem is data. All data points in different directions. Houses get struck by lightning and burn down, while others receive no damage at all. Some structures like commuication towers get hit by lightning hundreds of times a year, and nothing negative occurs. The same tower will get hit the day after it is errected and all equipment is destroyed.

I think it is safe to say that installing a LPS cannot harm a building or structure, but you cannot be positive it is doing anything to protect the structure or building it is installed on.

A positive lightning discharge was recorded in Japan a few years ago at 300KA. I don't care what LPS or any other TVSS technology you install, nothing is safe against that.

 

[DaveTap]

Re: Lightning protection

Originally posted by bob:
[QB] Lightning rods and down leads do not prevent a building from being hit by lightning.

That may not be true... Lightning like electricity takes the path of least resistance to ground. Typically it is an ionized pathway... which makes the saying "lightning never strikes in the same place twice" not only untrue but just plain wrong, since it almost always strikes the same place many times in quick succession too fast for the eye to see. Pointed rods connected to ground will neutralize any nearby ions making the air around the rod less conductive... the only problem is you just raised the ground closer to the source of the lighting by the height of the house making it the shortest path to ground...LOL

 

[don_resqcapt19]

Re: Lightning protection

Dave,

Lightning like electricity takes the path of least resistance to ground.

No!! It takes all paths.
Don

 

[bdarnell]

Re: Lightning protection

Originally posted by DaveTap:


Lightning like electricity takes the path of least resistance to ground.

Slight correction - Lightning, like electricity will take all paths of resistance to ground.

Here's an excerpt from a reference I have here in the office:

"Lightning protection systems control electrical discharges by directing them through a low-resistance path to the ground, avoiding passage through parts of a structure and reducing risk of fire or other damage. Air terminals (rods) fastened to the building intercept electric discharges, directing them through conductors to a grounding system and thence into the ground. The system was first invented by Ben Franklin in 1752."

 

[RCinFLA]

Re: Lightning protection

The primary objective of lightning rod is not to take a lightning bolt strike. This is a very common misunderstanding.

Pushing the charge that is building up to a sharp point will cause the E field at the tip of rod to be a very high potential that causes the charge to leak off gradually via local ionization of air at tip of rod.

By bleeding off the charge slowly as it is being created there is much less chance of ground to sky charge to build up to a point where a sudden large light bolt relieves the charge build up.

 

[bob]

Re: Lightning protection

The primary objective of lightning rod is not to take a lightning bolt strike. This is a very common misunderstanding

As the voltage builds in the storm cloud, the air begins to ionize. A down leader begins to migrate toward the earth. As the leader gets closer, objects begin to arc upward toward the leader. This includes poles, trees, towers and houses. The down leader will eventually connect with one of the upward leader and the discharge takes place. If the upleader terminal on the house makes the connection, the discharge is through the terminal and the down conductor. Since the air is still ionized you may see several repeated discharges at the same point. There are lighting
terminals that tend to "bleed off the charge"
but I do not think a single lightning rod provides
that type of protection.

[ February 17, 2006, 03:59 PM: Message edited by: bob ]

 

[ramsy]

Re: Lightning protection

Mike Holt's last newsletter "How to Protect Your House and It?s Contents from Lightning" references This IEEE Guide for Surge Protection of Equipment Connected to AC Power and Communication Circuits

The design and installation of the lightning protection system is not described by the NEC, but by a related document, NFPA 780-2004. Fortunately there has just been a major recent revision to this code, with strong improvements, especially in requirements to install surge protectors to protect the electrical and electronic equipment inside the house. The new code recognizes only passive striketerminating devices such as metal rods and heavy wires.

The later sections of this Guide provide more detailed information on the selection and installation of surge protectors than is provided in the NEC/CEC and NFPA 780.

Enjoy..