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So I am standing on the deck of the house we are rennovating ( http://home.austin.rr.com/gattisfamily/tres.htm ), watching a huge storm blow in, when suddenly it occurs to me that this is a metal roof house, on a hill, and I am being very, very foolish.
This house originally had a lightning-protection system on it (four rods and some twisted-aluminum running down to the ground) but I do not think it is salvagable.
My question is this: Does anyone have experience with installing a lightning protection system, and where could I find more information?
As always, thanks for the great advice, this is one of the finest forums on the net!
Cheers,
– Gary
Replies
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From "The Straight Dope" (a somewhat irreverant answer column) earlier this week - http://www.straightdope.com
Dear Cecil:
Everyone learns about lightning rods in grade school. There is the heavy-duty kind on skyscrapers that takes the brunt of bolts and conducts them safely to ground, and the delicate, sharply pointed ones that protect residences by bleeding off electric charge and preventing strikes. Having been well schooled in skepticism by our beloved Cecil, I tried to find a scientific study showing that rods actually ward off lightning, before plunking down dollars. No luck, except for manufacturers' marketing propaganda. I've seen a scale-model village successfully protected by tiny lightning rods from a "lightning" machine. But models don't always scale up to the real world. Do houses with lightning rods actually get hit less often than houses without? --John Glenn, N.T.A. (Not The Astronaut), San Francisco
Cecil replies:
You're thinking: What a stupid question. Everybody knows lightning rods work. People wouldn't have put them on buildings for more than 250 years (lightning rods were initially proposed by Benjamin Franklin in 1749) if there weren't a sound scientific basis for them, would they?
Well . . . maybe they would, maybe they wouldn't. We need to have a little talk.
Current U.S. lightning protection standards are embodied in a document published by the National Fire Protection Association known as NFPA 780. First issued in 1904 and updated periodically since, NFPA 780 codifies the traditional lightning rod installation, in which sharpened metal "air terminals" known as Franklin rods are connected to an earth ground by means of heavy conductors. A lightning bolt strikes a Franklin rod and is carried harmlessly to earth by the grounding apparatus, sparing lives and property. Though technically voluntary, NFPA 780 has been adopted by many local jurisdictions and government agencies and is the de facto national code.
Some years ago manufacturers of a new type of lightning rod using what's called early streamer emission (ESE) technology began agitating for a new NFPA code for their product, which supposedly requires fewer air terminals that can be placed farther apart than the traditional Franklin rods. An ESE terminal, described as looking like "a chrome cantaloupe with a chrome Frisbee around it and a little sharp prong on top and mysterious portholes around the sides," uses radioactive material to send a stream of ions aloft. This supposedly provides a path for lightning and guides it harmlessly to ground.
Most research to date shows that ESEs work no better than Franklin rods and fails to justify the claim that fewer terminals can be used. In 1993 the NFPA declined to approve proposed NFPA 781, which would have set ESE standards and presumably given the ESE industry a shot in the arm. ESE makers sued, claiming NFPA 781 had just as much scientific backing as NFPA 780. In a settlement the NFPA agreed to have ESE technology reevaluated by an outside panel.
The panel confirmed that there was no scientific basis for NFPA 781. But guess what, it said. There's no scientific basis for NFPA 780 (traditional lightning rods) either.
NFPA membership voted to approve an updated 780 anyway, but the NFPA standards council overruled them and announced its intention to rescind 780 unless somebody could give them good reason not to. While the NFPA wouldn't come right out and admit it when I called, I suspect the threat of another lawsuit was in the back of everybody's mind.
Proponents of traditional lightning rods freaked. A report from the Federal Interagency Lightning Protection User Group said, in essence, Come on, everybody knows this stuff works--if you rescind NFPA 780 it'll be back to the anything-goes days of the 19th century, when lightning rod con artists bounded. But there was an unmistakable air of desperation to the group's plea. Much of the evidence was from sources like the Iowa state fire marshal's annual report from the 1920s, which talked about barn fires. After 1950 research largely ceased; people just assumed traditional lightning rods worked.
They probably do work, but maybe not as well as was once believed. Critics of 780 point out that lightning remains a largely unpredictable phenomenon and that rods merely improve your chances rather than offering guaranteed protection, as the old code assumes. (Another beef: the committee in charge of 780 includes too many lightning rod manufacturers, who have a vested interest in maintaining the status quo.)
The NFPA standards council deferred a final decision "to give proponents of NFPA 780 an adequate opportunity to set forth the claimed substantiation for traditional lightning protection systems." Comments are currently being accepted; the group will decide what to do next at its October meeting. I'm betting the sparks will fly.
--CECIL ADAMS
*Casey:Great post!In my life lightning rod salesmen rank right there with the old fence, water softener(remember the steak knives as a prize to get you to let them test?), and aluminium siding salesmen.
*Very nice work, Gary. I especially like the way you put the house relative to the trees on the new lot exactly the way it was originally.-- J.S.
*Here is some recent info from the National Lightning Safty Institute August 30, 2001 Email NLSI Section 5.5.4 Should Lightning Rods be Installed on Modern Structures?by Richard Kithil, National Lightning Safety Institute1. HISTORY AND DEFINITIONS.Benj. Franklin perceived that lightning striking an elevated grounded rod would follow a "path of least resistance" to earth. His invention advanced fire safety considerably in those days and still holds true today. The deployment of (a) rods (now called air terminals since they are a termination point for lightning in the air) and (b) a series of horizontal and vertical straps or wires to (c) ground rods (so called because they are a termination point for lightning in the ground) make up the classis definition of a Lightning Protection System (LPS). A LPS can be defined as a "preferential path for lightning from intercept location to ground destination." Lightning can be defined as "arbitrary, capricious, random and unpredictable." When combining the aforementioned definitions, we should not be surprised to achieve less than 100% efficiency in our attempts to control lightning’s agenda.2. CHANGES IN BUILDINGS. Today’s buildings typically are not simple wooden or masonry structures as in the 18th Century. Modern buildings may contain: structural steel; steel rebar in concrete; metal clad siding and/or metal roofs; cast iron waste water pipes; copper water pipes in walls; cable TV wiring; telephone wiring; electrical wiring; metal wall studs; metal door and window frames, etc. 3. LIGHTNING BEHAVIOR AND EFFECTS.If lightning strikes a LPS on a structure, it is possible that transfer impedance (see IEEE 1100-1999 Powering and Grounding Electronic Equipment, pp. 61-78) may energize unintended conductors listed above. The magnetic effects of lightning also may couple to these unintended conductors. Casualties to people inside modern structures typically include: while on telephone; while in bath or shower; while washing at kitchen sink; while touching electrical appliance; while touching or near metal door or window. (Benj. Franklin suggested safety while inside could be obtained by lying in a silk hammock slung in the middle of the house.) According to an insurance study (Gugenbauer A., Linz Fire Protection Authority for Upper Austria) indirect vs direct lightning damage is about 100:1. This means that the LPS is of no merit in cases of indirect lightning strikes nearby to but not on the structure. NLSI suggests that detailed attention to bonding, grounding, and surge protection ranks higher in priority than the LPS.4. OPTIONS FOR CONSIDERATION .According to local situations, the following alternatives to ordinary lightning rods may be useful:(a) The electric power industry has adopted designs of tall masts or overhead grounded shield wires located above the structure to be protected. This can be observed on most high voltage power lines and on most distribution and substations. Here, the idea is to collect the lightning ABOVE the structure, not directly on it. (b) Following is from US Air Force AFI 32-1065, section 14.5, p. 10 "Explosives Facilities …that do not use structural steel as air terminals must use either a mast system or an overhead wire system. Since these systems provide better protection, and maintenance is easier, consider using this type of protection for other kinds of facilities."(c) Sometimes unconventional intercept design approaches might be considered. Perhaps rods installed in tall trees or on a tall pole adjacent to the house? An overhead shield wire installed atop a mountain cabin or a golf course shelter? Attention to detail with good grounding and installing high quality surge suppressors? Since lightning safety is a very site-specific subject, only you can make the best decision to reduce the risk to acceptable levels. 5. WISHFUL THINKING. Air terminals claiming enhanced performance fall into two categories.Radioactive/Early Streamer Emitter (ESE) and multi-point discharge air terminals have been researched and dismissed as ineffective (see R.H. Golde, Lightning, pp. 566-572. See other information is this site for more recent investigations). Vendor claims should be challenged by requesting proof of performance from independent third party peer-reviewed sources. If it sounds too good to be true – guess what – it is ! Training in Lightning Safety can be provided by the National Lightning Safety Institute Table of Contents NLSI Information Business Services Accidents & Incidents Personal Lightning Safety Information and Referencescontact NLSI Site Administrator with site problemsNational Lightning Safety Institute, 891 N. Hoover Ave., Louisville, CO 80027
*Gary, First off, what a job! Looks like is going quite well. I thought I had a big job "building" my own house but I'm not sure about it know that I've seen your project??? I live in the lightning capital of the US here in Tampa, Florida. Three people have already been killed here this year. The chimney I just completed is 27' tall with a steel cap and it looms high just asking to be hit. I know I can't prevent it but maybe I can lessen the blow. The steel cap is secured to the flue pipe and top masonry but not to any other part of the chimney. I took some copper stranded grounding cable and connected it to the cap. I ran the cable down the side of the chimney on ceramic insulators lagged into the bricks. The cable terminates into a 10' ground rod sunk into the ground approximately 5-7' feet from the structure. Since completed we have had several really bad storms and some very bad lightning. I think it may have already taken a hit but cannot be sure as there is no way to tell unless you are out watching it which I don't care to do. I had considered installing an in-line fusable link but this would only serve to tell if it was hit once and if it was and the fuse blew, it would be an open circuit and therefore usless until I installed another fuse which I would not do in the middle of a storm. So I just "trust" that its doing its job. I probably could have improved on the system by having a rod on the cap separated from it by some glass style insulator but couldn't find one easily and recalled my college meteorology classes where we discussed if the lightning just traveled a few miles through the atmosphere at a very high rate of speed to discharge, a few more inches will likley not offer much more added protection with regards to time, money and materials spent.Good luck with your project.Mike
*True lighting story --Pro golfer Lee Trevino was hit by lightning, and survived. His advice now is to grab a one iron and head for the clubhouse. Why? Because even God can't hit a one iron. ;-)-- J.S.
*LOL!!! Nice one John, and thanks to everyone for the great info! I am kinda getting the feeling that lightning rods do more for psychological comfort than actually deflecting lightning, but that alone may be worth it. Although we do not get many big storms in Austin, the ones that do blow through are sometimes spectacular. The fact that I still do not have a complete roof on the house yet, and had to spread sawdust all over the floors today, did nothing to take away my appreciations for the occasional beating we take. The house is on a hill, and the highest structure in the area, and I can certainly seeing it being struck, whether by Act of God or Nature is up to question ;-)So say I do want to put up a lightning rod. Any suggestions as to what would fit with the house and its style? I still have the old twisted aluminum rod, a few hundred feet of bent up pieces. Should I save that for a special project? Or hire someone to install something modern? Has anyone installed lightning rods before?As always, the feedback is appreciated, and sometimes hilarious.Cheers,- Gary
*I would think that lightning volts and amps would need a cable about the size of a large down spout. Most of the ground cable I have seen is smaller than the lead in that the power company laid for my 200amp 3ph service
*First a caveat: I consider myself pretty ignorant regarding things electrical... (But of course that never keeps me from sticking my neck out) ;)I have always heard that lightning rods do NOT get hit by lightning. That they are actually intended to discharge the structure's charge easily/quickly into the atmosphere, and thus avoid a dangerous buildup of charge that will discharge quickly/violently in the form of a lightning bolt.Is this way off base?Flame away...
*Yup Stray, they do get hit, as thousands of photos have shown. Gary: If you are really serious abut doing a technically good job, download a demo version of Quickfield (or similar) off the net, learn to use it, and model the electric field of your house and adjacent trees, and the neighbors houses. Rerun with different aesthetic lightning rod installations and use the one that give the lowest field at the roof and highest at the rods. Tie the roof to the lightning ground wire also. #4/0 will handle 99% plus of magnitudes, but you need to pay attention to mechanical fastening (tests I've run at 300,000Amps did not fuse #4/0, but pulled the wire out of the connections due to current generated magnetic forces)DO NOT tie the lightning ground to your white or ground wire at the box. Best to have a separate and better ground for the rods. The subject of collateral damage due to induced currents vs. fire danger to the building is a whole other area of studies, cheap point of use surge protectors plus insurance may be your cheapest way to go. There have been literally millions spent on protection implementation due to collateral damage at some critical military facilities.
*Gary, I have a house out in the open on top of a hill near Bryan. I had a guy from Brenham install lightning rods and he used a braided copper wire about the size of my pinkie . . . half inch or so. He put rods on all four corners of the widow's walk and one on each gable peak about 2 ft. from the edge. He has all the rods tied into three different lines going to three grounding rods.
*Fred,First let me say that your house is breathtaking!!! If it is not being too intrusive, approximately how much did the Brenham guy charge you? Have you ever had any strikes out there? Cheers,- Gary
*What a coincidence, there was a piece on lightning on the TV last night. Some guy in Florida, at the Univ of FL I think, has the world's only lightning research pad. These guys fire rockets trailing wire at clouds to attract lightning. Even in the midst of lightning storms they aren't always successful.Anyway the big message from the show was that even when operating within a lightning storm is is exremely rare to be struck. Even airplanes only get hit infrequently.The next message was that even today we really don't understand lightning at all. In fact as research continues, according to him, we are finding more and more different kinds of lightning. Each one has a little different behavior. Also, we apparently are walking through an electrical field all the time, in the order of 200V.Oh he had a test house there too. This house has instruments in it to mesure the effect of lightning on houses. It was only a quick picture but I didn't see any lightning rods. Did see lots of protection on incoming wiring though.Check it out. Go to their web site and see what the real expert says. Bet he would agree that rods are a waste. Maybe a wire over the house, but not rods.
*Don --The reason that you don't need such a big cable for lightning is that the lightning current lasts only a tiny fraction of a second. It may be hundreds of thousands of amps, but it's gone before it can heat up the wire very much. If you pull a full 200 amps on your service, it'll take a few minutes or more to heat those wires up to equilibrium.-- J.S.
*xJohn , i guess that is a good 'nuff explainin' but I thought that it was a lot of juice to push through such a small straw.
*I'm pretty sure he's been struck TWICE. But that was a great line, for sure.
*Put your fuse in parallel in the line, not in series. In the event of a strike, the fuse will probably blow anyway, even though it is not the only path to ground.
*Fred...the only thing I do know about lightening.....I learned in flight school.....and that is aircraft....especially small aircraft....get struck ALL the time....and after a bunch of scientific stuff is explained.....the damage consists of small pin holes in the exterior skin. Aside from that, everything I've read seems to suggest the lightening rods don't really do much. But....maybe better safe than sorry. I can tell ya...from personal experience.....the when your house is struck......and you are on the phone......the "bang" is loud enough to affect your hearing for a few days! Jeff
*Thanks Gary,The moving guys were Yoakum House Movers.. . . very professional and knowledgeable. Mr. Yoakum started out helping his dad move houses with mule teams. It's hard to say exactly how much the moving itself cost because we had them do some restoration work on the porches and they replaced some of the structural beams. But it killed about $100,000.00.One of my sons and I like to go out there (we don't live there yet)and watch thunderstorms coming in; watch lighning. You may have noticed the view is great. We,ve not been there during a strike on the house. I've seen one of the electric poles get hit. I think some of the pictures on the web site show the placement of the rods. The finial on the cupola has one too, but it's only been there a couple months.If anyone would like to check out my "project" here is a web site my son maintains:http://www.geocities.com/annajo1009/index.html
*The Coast Guard has lightning recommendations for boats.A boat mast of proper height with a wire to the water will protect a boat from the majority of strikes. The height is determined by the angle of the "cone of protection."One could argue that unless a lightening rod is very high relative to the roof the whole hose is not under the cone of protection and that is why many methods do not work.
*oops, I had house moving on my brain. They are both in Brenham. The lightning rod guy charged about $2400. If you're interested let me know and I'll find his name and number. He is a professor at Blinn that did lightning rods part time.
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So I am standing on the deck of the house we are rennovating ( http://home.austin.rr.com/gattisfamily/tres.htm ), watching a huge storm blow in, when suddenly it occurs to me that this is a metal roof house, on a hill, and I am being very, very foolish.
This house originally had a lightning-protection system on it (four rods and some twisted-aluminum running down to the ground) but I do not think it is salvagable.
My question is this: Does anyone have experience with installing a lightning protection system, and where could I find more information?
As always, thanks for the great advice, this is one of the finest forums on the net!
Cheers,
- Gary