Just had a new roof put on our barn. Weathervane tops it off but may make a tempting electrical ground. 200 feet away stands a church steeple that bristles with lightning rods that I would hope would be the preferred target in an electrical storm.
Seems to me I have heard both that lightning rods are good protection, others say that they are a total waste of money. I do wonder if the standard house type system can really be effective to a direct strike seeing that lighting is God’s answer to molecular disintigration. Can they really take the hit? Or are they just something to make us feel better.
wsf
Edited 4/12/2002 1:24:12 PM ET by WFLATHER
Replies
flather... my reserch on lightning rods was inconclusive.. seem more like black magic than science.. but whatta i no.. the theory is NOT that they can take a hit and conduct it to ground..
the theory is that they.. deliver like charged ions from the ground and distribute the like charged ion umbrella over the protected structure .. since same charges repel.. the lightning will NOT strike a protected building...
now wwhatta ya think of that ?
on the old board we could easily post Hot Links to show you information sites.. but this s u c k s...
Mike Smith
Rhode Island : Design / Build / Repair / Restore
It depends what you want to protect and how much you're willing to spend to protect it. TV transmitters can suffer hundreds of thousands of dollars in lightning damage if they're not adequately protected, and some stations spend thousands of dollars just on ground rods for lightning protection. They do that to get under 5 ohms to ground.
-- J.S.
I don't think it's black magic at all.
Every building I've done has lightning protection. Arenas, office towers, hotels, hospitals, equestrian arenas, barns etc.
I've also had them installed on homes as well.
But it probably doesn't have electrical storms out where you are so not to worry, right?
Cheap insurance,
Gabe
well, gabe.. i've had a couple buildings protected too.. but i still don't think they have much of an explanation of the theory of protection..
what is your explanation ?.. or anyone else out there....ships get hit.. sailboats get hit.. airplanes get hit..
the lightning rod:.....is it a conducter for the lightning bolt ..or a cone of protection?
well ?Mike Smith
Rhode Island : Design / Build / Repair / Restore
c'mon gabe.. let's u & me flame this board...this site s u c k s.. now fred has abandoned us... who's left to have "discussions" with ?
c'mon, u opinionated old fart.. tell me about lightning rods... and ben franklin... hah,hah, hahMike Smith
Rhode Island : Design / Build / Repair / Restore
Hi Mike,
Not a lot to tell. Electricity follows the easiest route to ground. Through your building or outside your building.
But you already know that you reprobate.
Gabe
who u callin a reprobate ?
now.. the theory of lightning protection is not to act as a conductor for the strike to go to ground...
as we say in france... au contraire...
the conductors are to give a path for the ions to form a cone of charged ions over the building.... since they have the same charge as the lightning .. the lightning will be REPELLED and find someplace else to strike...
now .. if that don't sound like black magic.. i don't know black magic...
but think about it.. what conductor could possible survive a direct hit from a lightning bolt ? not many ... so.. the cable and roof spikes are NOT conductors for a safe path..
but then what the hell would a general contractor know about anything besides fishing or golf...Mike Smith
Rhode Island : Design / Build / Repair / Restore
Radio and TV towers do survive multiple lightning strikes. The chief engineer at a local station could probably tell you a lot about it.
-- J.S.
Mike,
I would be calling u a reprobate.
Cone of protection my butt.
Sure is hard to insult properly on this new format, but I'll get it yet.
Try trying to find a ground for lightning protection when the water table is 80 ft. down on a sand hill.
Must be a full moon out, Mike's outside collecting ions to coat his roof with.
Gabe
So Mike?
You moving to France to get away from the wrath of Gabe?
I thought you liked Rhode Island.Excellence is its own reward!
W'all blow me over, Gabe is right.
Dat der cone of protection is the "cone" within which lightning that would normally strike a tree or the ground will instead strike the rod. The "cone" is only a rough guess and rule of thumb. If you want to get precise on lightning rod placement and "cone" area, you need to do a complete electric field model (using Quickfield or Ansys for instance) of the structures.
Do you need lightning rods at your place? Go to the NASA lightining web site (I'll let you seach yourself) for their optical transient detector (OTD) printouts, satellite shows how many lightning strikes were in any area of the world last year, judge for yourself by that. Almost NOBODY has lightning rods in Seattle, everybody in the countryside better have in Tampa.
Thats why there is one on top of my 26' chimney. I'm 7 miles east of Tampa!
Mike
Yessir... gimme one cone of protection, three rings of power, a dowsing rod, and a partidge in a pear tree.
Well, my grandfather, who spent years as an underpaid ticket puncher on passenger trains, always said that he could never be electrocuted because he was a poor conductor.
If the cone of protection was anything like the cone of silence, none of the electrical in the house would function!
Rich Beckman
A conductor.
Gabe
Facility Electrical Protection (FEP)
Whatcha talkin about Mike? It is easy.
You must be a real old dog havin a tough time with new tricks . :)
Oh yeah!
How a Lightning Protection System Works
Here is the "cones" business.
If you have trees taller than your house they will work as good as lightning rods. But after seein trees struck by lightning I have to wonder how a lightning rod ground wire would look after a strike.
Edited 4/13/2002 6:57:41 PM ET by Blah
blah.. i knew i wasn't making that explanation up.. here's the same thing with a different link description ..
http://www.lightningrod.com/manual5_how.html
these "hot" links don't work like they used to.. i have to copy & paste them
is that u BLAH ?
Mike Smith
Rhode Island : Design / Build / Repair / Restore
Edited 4/13/2002 10:47:51 PM ET by Mike Smith
Mike,
Cool link. I like the graphics.
I like how it explains the upward ion movement. Thats the reason some folks say lightning strikes from the ground up.
And Blah, the ground wire on a rod will suffer no damage if it is properly sized (not something like 16 or 14 gauge) It just acts as a path for the flow into the ground rod and earth ground. Trees are damaged because they are not good conductors like a copper straned wire and ground rod are. Sure they conduct the stroke just becuase of the high voltage of the strike and their heigth and proximity to the charged cloud but if they were better conductors like a piece of copper wire, they would likey just pass the charge into the ground instead of burning and exploding into flames like they do. The sap content and flammable nature of a tree don't help either.
As a side curiousity, I'm thinking about installing a huge fuse in parallel to the rod and ground wire on my chimney so I can tell if it ever gets hit.
Mike
About a year ago I spent some time and did my own research on this topic and came across a US government study which was extensive, expensive and covered many years. Their conclusion was that there is NO scientific or statistical evidence whatsoever that shows that lightning rods protect a building from lightning strikes. Any evidence to the contrary that I came across was ALWAYS and without exception provided by someone who was in a position to gain in some way commercially from it (ie. sell you a system). I made my own conclusion to file the topic along with astrology etc., and have dismissed any inclination that I might have to install lightning rods other than for decorative purposes. You might want to do your own search to satisfy yourself and find that study ; it was available on the internet. IIRC there was also no evidence to show that lightning rods did any harm as well.
Regards - Brian (a believer in only "hard" science)
Brian,
But why does NASA then publish their report (I have the doc but don't know the number off hand) regarding the 18' or so fiberglass mast on top of the Space Shuttle launch pad and the numerous hits it takes PER DAY during a Florida thunderstorm and how severe damage to the pad, orbiter, etc would occur had the electric discharge not been rerouted via the LPS (Ligthning Protection System) into the ground?
Not fighting with you of course, just pointing out how gov't opinions and reports can differ.
Mike
Just because the Gummint studies it and reports on it does not necessarily make it true. This is the same Gummint whose EPA prints more Junk Science that is utterly worthless and barely anecdotal. Read Steven Milloy's column on Fox News web site about Junk Science for many examples. Even the National Academy of Science and National Research Council, that are supposed to be beyond reproach, have been sucked into performing some highly biased and questionable studies. Lightning rods work best when they DON'T get struck - it means they have done their job of dissipating the strong ionic charge in the ground into the atmosphere, thus preventing the strike. Among those who design and build such systems, I believe they are now called "Air Terminals." This term more accurately describes their function. If they don't work, pls explain why the Empire State Bldg gets struck so many times per year, and sometimes per storm. Unfortunately, it gets struck because it isn'tefficient enough at dissapating charge. I would say that the concept of an air terminal passes the common sense test - it is just a matter of making that concept work properly.
The University of Florida has a lightning research project/team/nutcase/guru/whatever, who writes about lightning frequently, based on a setup in some open field near Gainesville, using - GASP - real lightning. He has published some results that influence how to protect a sailboat, etc. Beyond that, his work passes the "Common Sense Test." If you want to read some other work that passes the CST, get a copy of the Army's explosive safety manual. It has page after page of how to protect structures against lightning. Now, the bulk of the scientific basis for that document came after the disastrous Lake Denmark, NJ, explosion caused by Lightntng back in the 1920's. We have had several threads in the old site that addressed it. One of the better was about the ground plane system named after some man that requires an extensive network of rebar grounded together in concrete slabs. His work came just before or after the beginning of WW-II, and laid the basis for lightning protection of several tens of thousands of ammo storage igloos worldwide, along w/ ammo and explosive production buildings. Most of these bldgs are in the tornado belt of the US - Iowa, Kansas, Oklahoma, Arkansas, Texas, Louisianna, Tennessee, Indiana, Illinois, Wisconsin. I would say there are conservatively 50,000 bldgs in this complex. I cannot recall any lightning caused significant damage in years to any of the protected bldgs (Note: that's a personal recall), but when it does occur, it would be dramatic and cause a safety investigation that made great waves. I did, however, witness a lightning strike that caused a fire in a house on an ammo production plant in Iowa in 1978 or 79. Strike was adjacent to the house; induced high enough current in the wiring in the house parallel to the bolt to cause an arc in an electrical box and start a fire. Fire Dept was less than a mile away and got there in time to minimize damage to minor enough to not affect habitability of house.
DonDon Reinhard - The GlassMasterworks - If it scratches, I etch it!
Very informative discussion. I will have to search for the NASA lightnign strike map and see if our part of Central PA is prone. I don't recall anything except the very occational lightning strikes being reported around here. I wonder if the nerby church steeple offers any sort of collateral protection for us.
Cape Canaveral and area, at least according to the Space Center tour guides, receives more lightning strikes than anywhere else in the US, if not the world. If I build there, and built such tall structures, I would want serious grounding as well.
I will also have to read up on the Cone of Protection scheme idea. But later, right now I have some ale to bottle....
View Image
Yes I'm blah.
Actually, I believe lightning rods work by diffusing charge...gradually....which for a charged cloud may be several seconds rather than .0001 second.
Electrons will concentrate and diffuse first from a sharp or pointed surface. As a charged cloud approaches a building (or tree), the charge differential builds (large blunt objects will have electrons stripped by the dry air, much as will a block of styrofoam that you rub). But a lightning rod emits electrons and thus the charged cloud will begin to 'bleed' its charge. I know its far more dramatic to think of lightning actually shunting itself through the rod/cable into the ground, but face it, if that happened, the rod/cable would melt, anything metal touching these would become an instant conductor of hundreds of thousands of volts, houses would catch fire from the heat and people touching anything metalic would be electrocuted.
bruce.. exactly....the thought that a braided copper conducter hanging down the side of the house was going to absorb a direct stroke and conduct it safely to ground is mind-boggeling...
the net sum of this discussion is that the study of lightning theory is still "black magic" and better minds than mine still disagree on cause & effect....
so.... on the grand scale.. with 1 being ludicrous. and 10 being something that can be readily demonstrated.... i'd put magnetic therapy and copper bracelets at 1....
the strength of 16d common nails at 9.. and lightning theory at 5.5 ....
but hey, whadda i no ?Mike Smith
Rhode Island : Design / Build / Repair / Restore
Bruce:
Lightning rods do dissipate a little charge, but only a little, enough to mess up AM & HF communications (<30 MHz, which is why you don't see fuzzy TV or FM (>52 MHz). Lightning still strikes the rod. The typical lightning strike is only about 15 kA and lasts 5 microseconds. That does not even get 10 AWG wire warm, let alone 4/0. The ground conductor does not fuse or melt, the duration is short.
hey mike, does reprobate = liberal, I can't mind my websters dictionary this morning, and I didn't think name calling was allowed anymore. Happy april fools day, and dont forget to mail your 4868.
bb.. i wuz going to go to work.. but i'll digress another moment to reply... good to see you in a post..
rep·ro·bate Pronunciation Key (rView ImagepView ImagerView Image-bView ImagetView Image)n.
A morally unprincipled person.
One who is predestined to damnation.
so , since the pharisees did not think of Jesus as a conservative.. do you think they called him a liberal ?.
and what about copper bracelets....
as to april fools day.. here in RI & Mass we get an extra day because of Patriot's Day.. and since i incorporated , our due date is March 15 ( the ides )...so we always make our personal filing with time to spare..
hope all is well with you and yours.. Mike
Mike Smith
Rhode Island : Design / Build / Repair / Restore
Edited 4/15/2002 8:32:01 AM ET by Mike Smith
Uh, wasn't he an ultra-conservative when it came to religion ?.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
This may be a little off the point, but the discussion reminded me of this:
Back when I was in the Army, we had a fuel truck driver that wasn't terribly bright. Didn't put the fries in his happy meal.
On his fuel truck there was a small metal cable that was supposed to be hooked up to trucks before you stuck the hose in the tanks. That was supposed to dissipate any static electrical charges so there were no sparks between the trucks. But this genius had an idea - He backed his truck up to a metal fence at night, ran the cable out, and hooked it to a metal fence. He said that if lightning hit the truck the charge would travel through the 1/8" cable through the fence to the ground, so his truck wouldn't blow up.
Edited 4/15/2002 8:33:01 AM ET by Boss Hog
If you protect your building with the rods you also need to protect the electronic items inside with a lightning protector on the whole house electrical panel. I had a old GE unit with not indication if it was good or bad. I changed it out to the new type that is a 220 volt breaker and a lightning protector all in one. Some manufactures have one that just plugs into 220 breaker slot and it is not a dual purpose breaker and lightning protector. I have had this protection for 35+ years and no damage to anything. There are 6 other homes on my blocck and every one has had a TV or Microwave damaged by strikes. You also need your Telephone to have the best gas tube protector. If you have cable you need a protector that protects the outer and inner wires of the coax. Many cable companies have the outer shield grounded and the lightning can strike the items on the pole outside your home and come in on the inner wire. I bought a special unit from Jerrold and put a tag on it to let the cable company know that my protector was subscriber owned. Larry
Here is the NASA site with the basics for the lightning maps, follow the links on the site for details of your area.
http://thunder.msfc.nasa.gov/otd/
I'd love to see the actual reference for a guvmint study that actuall said lightning rods were only cosmetic rather than simple anecdotal evedince that a "study was done".
GRRRRRR!!! - You guys are making me do the same work twice now!!! Just found this link. See parag. 3.3 where they refer to "vendor-inspired marketing tool"... References are at the bottom of the page. http://www.lightningsafety.com/nlsi_lhm/explosives.html
Regards - Brian.
Thanks for the reference Mark:
Some of the confusion in this discussion thread is due to the fact that the reference was written to address lightning protection for explosive storage.
There was nothing in the report I disagree with, it just is that a jump cannot be made that says don't bother putting lightning rods on houses, as that is a whole different situation. In explosive facilities, any arcing at all in the storage is hazardous (obvious), hence one wants to keep lighning currents on the facilities to a minimumm both in magnitude and STATISTICALLY.
Some quotes from the report.
First, the caveat to the phrase that says the 248 YO lightning rod method is not applicable:
"For more complex facilities, where electrical systems/electronics or explosives or volatile substances are present, the 248 year old design is questionable." True, one wants to minimize both magnitude and rate of occurence - the statement "more complex facilities" limits the rejection of Lighning rods to just that case.
2nd:
"Lightning "prevention" exists only as a vendor-inspired marketing tool."
How true - The first I heard of lightning "prevention" was at the 1977 FAA sponsored syposium on Lightning. A presenter (vendor) was pushing stringing gobs of barbed wire over sensitive facilities to "dissipate" lightning - received by audience of specialists very skeptically to say the least.
3rd:
"In 1876 JC Maxwell suggested that Franklin rods on buildings attracted a greater number of flashes than their absence. Such rods should not be located on explosives storage structures."
Maxwell (of "Maxwell's equations fame) is correct, which is why lightning rods on explosive facilities are statistacally not a good idea**. On houses, only one bolt to an unprotected frame structure = fire, multiple to lightning rod = no fire, but maybe zapped phone etc. Rather lose the phone than have a fire. ** Grounding the sturucture conductors (e.g. steel) IS still a good idea.
4th:
"Downconductor pathways should be installed outside of the structure. Rigid strap is preferred to flexible cable due to inductance advantages."
Good points for lightning rod ground conductor installation (implied that even on explosive facilities they may have a use if faraday cage or grounding of concrete and rebar and structural steel is not feasible)
I might add that testing I've personnaly done at 350 kA shows that 4/0 Cu cable failure is not due to fusing, but to mechanical forces from the generated magnetic field literally breaking the wire if it is allowed to move, so RIDIDity and tight clamping (as in every 6 INCHES)are important. Don't just drop the ground wire down the side of the house.
BTW, there used to be a big set of discussions on whether ball or point rods were better. The field analysis tools available nowdays (e.g. Quiockfield) say that balls are better, primarily because the small amount of charge that really is dissipated (lightning still strikes) causes radio frequency interference. (Ref 1975 study on Boston's Logan airport shutdowns due to HF communications losses during storms - sorry Mark, not on the web to reference)
Art B.
Mike - Good question - I'm guessing the dissimilarity between a metal space shuttle sticking up in the air with sensitive electronics etc. to protect and a house on the ground would account for at least some of the difference. I don't believe the two conditions are similar enough to allow us to call the two different reports contradictory.
Don - Pardon me Don, I don't quite follow you; does the Empire State building have lightning rods or not? And would removing them if they have them not be an effective way to judge their value? My guess - removing them would not significantly affect the frequency of lightning strikes. I think that a blunt- roofed Empire State building would be struck as often and with similar consequences (maybe less often???). I believe that grounding of the structure is of more value at preventing damage when lightning does strike, though.
Would you agree that a car is a good place to be in a lightning storm? Why? - it has no lightning rod? Because the exterior forms a conductive shell (technically a "Faraday cage" IIRC) which directs the energy around the occupants and harmlessly into the ground. (BTW - the tires do not insulate at all, particulary when wet, as is commonly thought. Because of their high carbon (they're black) content they're good conductors, which contributes the the lightning safety of a vehicle.) Also, IIRC the lightning will stay on the surface of an object if it can rather than penetrating deeply to find ground.
In my personal view there is still no hard scientific evidence that lightning rods decrease lightning strikes to buildings or reduce the damage from them. It's a hard thing to prove - we know so little about it. But I won't think any less of anyone who believes otherwise either - at this point in mankind's knowledge it's a faith thing, kind'a like believing in a God. The consequences of not believing can far outweigh the benefits of believing. ; )
Also be aware that my beliefs are subject to updating in the future! : ) Bring on some good links you guys!
Regards - Brian.
> does the Empire State building have lightning rods or not?
Yes, it does. Empire was the main site for radio and TV transmitters in NYC prior to the completion of the World Trade Center, and when everybody moved to WTC, WCBS kept a backup transmitter at Empire. That kept them on the air during the first terrorist attack in 1993. Prior to 9-11, WCBS and WNYT were using Empire for their new digital TV services. Now it's the primary for the regular NTSC service of WCBS, and a few others, WABC IIRC. They've also had radio up there since the building was new. Empire has been getting hit by lightning and conducting it safely to ground for 73 years. Its lighning systems were installed and are maintained by the broadcasting tennants.
Lightning rods do not prevent lightning. Instead, they make other things less likely to be hit and damaged by lightning, by making themselves more likely to be hit. They are designed to survive multiple strikes, and many have survived such strikes.
Not all lightning strikes are created equal. Pro golfer Lee Trevino was hit by lightning, and survived. Now, when clouds gather, he grabs his one iron and heads for the clubhouse. Why? Because, he says, "even God can't hit a one iron."
-- J.S.
The Empire State Bldg IS a lightning rod - for ll of lower Manhattan. It is a true lightning rod, in that it gets struck very frequently.
It is impossible to prove a negative. I think rods,when installed as air terminals, work. If those bldgs so protected don't get struck, I think it INFERS that they work. But it is impossible to PROVE they work, ie, don't get struck. Recall, the purpose of an air terminal is not to get struck, but to bleed off charge through an extremely intense electric field at the very sharp tip. Meanwhile, as an old time ammo manufacturer, I'll put protection on my bldgs tillsomeone proves it doesn't work.
DonThe GlassMasterworks - If it scratches, I etch it!