Lightning Air Terminals

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Probably neither.

First and foremost, any air teminal, strike termination device, or lighting rod used for a LPS should be meet all the criteria found in the ANSI/UL96A and the NFPA 780. If the device is listed and meets the above standards, the configuration of tip has very little importance when considering performance of the overall system.

As stated by Ron, other design criteria, such as safety of persons while on a roof or adjoining structure may be of greater consideration.

The code does give some guidance. Most of the NFPA 780 is silent on the matter unless you look real close.

The notes to Figures 4.6.2.1 and 4.6.2.2.2 state: "Air terminal tip configuration can be sharp or blunt." The figures show both type for reference.

More to the point, no pun intended, can befound in Section A.4.6.21 of the NFPA 780.

This section states: ""Recent experiments described by Moore el at. in the Journal of Applied Meteorology suggests that the optimal air terminal tip radius of curvature for interception of lightning strikes is 3/16" minimum to 1/2" maximum."

So, not too flat - not too sharp is probably your best bet. For 99% of your conventional installations, the difference in performance is NOT measurable.

And MOST importantly, stay away from any and all ESE, radioactive, or other non-conventional products found on the market today.
 
Do you have any reasons for this statement?
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Not that Brian needs any tactical air support, but ..... from a design professional standpoint, if you need to go in front of a judge and they ask you why you used a lightning protection method not documented by a nationally recognized organization like NFPA, especially in their lightning standard 780, the stuff will hit the fan.

Just my opinion. and as a side note, I like Franklin's theories better anyway. ;)
 
Let me clarify that many non-conventional air terminals have been listed under the ANSI/UL 96 standard. However, they have to be installed per 96A and the NFPA 780 to be a compliant component of the full system.

So if you would like to use one of these devices in place of one or more or even all the conventional rods, great. But the quanity and location of the devices must be as if they were conventional rods.

Many of these devices make the claim that one device can protect an entire structure with one down conductor using the Collection Volume Method or some other non-recognized theory of protection. So, if one were to design the LPS for the same structure using a NFPA 780 compliant method, say the rolling sphere method, and use an ESE device where one or more of the air terminals are shown to be needed, I would have no objections to that.
 
bphgravity said:
Yes, research.

A good start would be here:

http://www.lightningsafety.com/nlsi_lhm.html


All the papers in Section 5.4.1 - 5.4.14 provide a good basis of information and research on the subject.

There are MANY, MANY, more...
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Yep, go right ahead and ignore the empirical evidence....that is contrary to the current state of scientifically proven (??????) lightning THEORY.

Prof. Moore - whom you have cited earlier, and who is now Professor Emeritus, eg. no longer does actual research - clearly acknowledged that there is mounting evidence that the current understanding and state of science is highly questionable and that some of the experimental systems have shown phenomena that can NOT be explained (away) by current science.

Some conspiracy theorist suggest that one of the main reasons why 'non-conventional' lightning protection systems are sooooo vehemently opposed because of their weaponization potential and all the accompanying implications.

BTW; I used to be a sceptic and you may can tell I am no longer one, but it is only limited to one system that proven itself to be very succesful. You can tell me that based on science the bumble-bee should not be able to fly, but I don't think the bumble-bee cares much about that.
 
Here's what the Federal Courts think about ESE systems. Hmmmmm!!!! :grin:

Roger
 
weressl said:
Court decisions have very little to do with science, just that his 'expert' has a bigger one than the other's 'expert'.
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Laszlo, maybe you should read up on what took place in the courts over the last 15 years, a lot of it (if not the majority of it) was based on scientist and engineers studies and findings.

I admit, I didn't see your name in any of the reading I have done in following this over the years so I anxiously await the findings of your experiments. ;)

Roger
 
I will be the first to admit that there is much more that I don't know or understand about lightning and lightning protection than I do know and understand.

I can say the same thing about electrical theory in general and the NEC for that matter.

But I really don't have to know or understand. ESE and other non-conventional systems are not recognized by the NFPA or ANSI/UL standards. Period. One day, science and evidence may prove the effectiveness and performance of ESE and other non-conventional methods and lead to these systems to be included in the NFPA 780 and ANSI/UL 96A standards or perhaps a completely new standard just for these systems.

But we are not there now, so I don't and can't support them. And the fact is that right now, there is much more substantial research showing these system not only not be effective, but even potentially dangerous. And that is not good.

In all honesty, the NFPA 780 and the conventional system makes NO claim. A compliant LPS per the NFPA 780 and ANSI/UL 96A does not guaranty a lightning strike will not occur and it doesn't guaranty the protected structure will in-deed be protected.

What these standards do provide is a means to analyize the risk, design suitable protection, and then cross your fingers that your structure never gets struck but if it does, the LPS works.

ESE manufacturer's are making outlandish claims. They go as far to claim prevention let alone protection. And that is wrong.

Here's a report from a recent incident that occured just down the road from me:

This report concerns damage from a lightning strike to the Marriott Hotel in Marco Island, Florida, which occurred on August 23, 2010.

The strike sent a bunch of clay tiles crashing to the ground in an area near a swimming pool. The fallen tiles crushed a table, bounced around and broke a window. There was also electrical damage. Luckily, no one was injured. The damage area was on the southwest corner of the building.

The structure previously had a conventional lps that was replaced with a "Preventor" ESE device during renovations several years ago. The Preventor ESE system had 2 down leads. The distance from the ESE rod to the damaged location was about 204' from the rod to the rear area of the building where the damage occurred. The rod was 94' to the front of the building.

Four photos of the incident are attached. These show location of the struck corner of the building, two photos of the ESE device and its location, and the damage to the roof.

Abdul Mousa, Ph.D., P. Eng., Fellow IEEE

Lightning protection consultant

Vancouver, Canada
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I can't attach the phots as the file is too large for the server. But the fact remains that here is evidence of an ESE system that did not prevent, protect, or do ANYTHING. Now, would had a conventional LPS protected against this strike? We will never know, but I do know the hotel's insurance is in no rush to pay the claim. They most likely won't.
 
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