lightning rods

[Poor Flick]

AFAIK this would be where to ask this.
Anyone know the real facts about lightning rods on buildings? We had a direct or very nearby hit last spring. It damaged two TVs and a surround sound system. With all of the reading I've done it seems the theory is to give lightning a very low resistance path to ground around structures to prevent lightning from using wiring outside and inside the building to find ground. There are differing viewpoints all over the internet and here to the point its now confusing. Also I've been working on my house for some time making it into a sort of country type farmhouse style and some decorative lightning rods would look good and hopefully serve a purpose.
One thing I can't understand is if lightning is on its way down from thousands of feet up, how are some conductors at the last 20 feet of travel going to alter its course?

[goontron]

Re: lightning rods

IIRC, what a lightning rod does is remove change from the air. i can connect a little neon light to my 100ft antenna and it will light on a cloud to cloud strike or cloud to ground.

[Poor Flick]

Re: lightning rods

goontron,
I have read similar where the idea is to equalize the charge difference between the ground and the air through the rods. The writer also stated these equipped buildings rarely are struck. Before reading that I first thought they were designed to attract and safely route it to ground. That would be a noisy and dangerous scenario! I didn't know what to believe.
So you agree that the air terminals are constantly working to equalize the charge difference to reduce the chances of a strike?

[goontron]

Re: lightning rods

goontron,
I have read similar where the idea is to equalize the charge difference between the ground and the air through the rods. The writer also stated these equipped buildings rarely are struck. Before reading that I first thought they were designed to attract and safely route it to ground. That would be a noisy and dangerous scenario! I didn't know what to believe.
So you agree that the air terminals are constantly working to equalize the charge difference to reduce the chances of a strike?

thats what im lead to believe. though if a strike is to occur it would rout lightning to ground aswell.

[Poor Flick]

Re: lightning rods

Thanks, goontron!
If anyone else has input I'm listening!

[redwire]

Re: lightning rods

I took a course on lightning protection and was surprised to learn it does not always take the shortest path.
It zig-zags and can go around a lightning rod and then nail the brick on a building! There are dozens of different arrestor designs out there but it is not easy to test them.

There is also the National Lightning Detection Network, NLDN which records the location and strength of all major strikes in the USA. It is useful if major damage happens and you want to know how strong the strike was. But I think it is a pay-per-use database.

[joshnz]

Re: lightning rods

One thing to take into account is 30000Amps if you catch one.
Need good grounding and large conductor with no sharp bends.

[Longbow]

Re: lightning rods

Fortunately there are volumes of information on lightning research and recommendations free for the asking. Tons of articles relating to lightning here at NLSI: http://www.lightningsafety.com/index.html

Some discussion of grounding here:
http://www.solacity.com/grounding.htm

Of greatest importance with lightning protection is grounding. The rod has to look like a more attractive path than anything in the surrounding area, and making it so is more difficult than it appears. I would especially recommend reading material on the Ufer grounding system.

Home electronics will easily smoke even without a direct lightning strike. Usually a pulse enters a residence on cable shields and tries to flow to the service ground whilst traveling across the p.c. board. This is because cable service entrances are rarely bonded to the electrical service ground. Or, the grounds are at multiple sites making them useless for lightning or for electrical shock protection. My opinion is that protectors with gas discharge tubes are the best insurance for protecting home electronics, but nothing is 100%.

[goontron]

Re: lightning rods

Fortunately there are volumes of information on lightning research and recommendations free for the asking. Tons of articles relating to lightning here at NLSI: http://www.lightningsafety.com/index.html

Some discussion of grounding here:
http://www.solacity.com/grounding.htm

Of greatest importance with lightning protection is grounding. The rod has to look like a more attractive path than anything in the surrounding area, and making it so is more difficult than it appears. I would especially recommend reading material on the Ufer grounding system.

Home electronics will easily smoke even without a direct lightning strike. Usually a pulse enters a residence on cable shields and tries to flow to the service ground whilst traveling across the p.c. board. This is because cable service entrances are rarely bonded to the electrical service ground. Or, the grounds are at multiple sites making them useless for lightning or for electrical shock protection. My opinion is that protectors with gas discharge tubes are the best insurance for protecting home electronics, but nothing is 100%.

my 100ft antenna has neon bulbs for the low power corona (streamers), and gas discharge tubes for the higher power nearby strikes.

[selldoor]

Re: lightning rods

We had a direct or very nearby hit last spring. It damaged two TVs and a surround sound system.

One question might be was the damage caused by the lightning or by a surge in the mains voltage?

If the latter then protecting your building from a lightning strike using rods is
unlikely to make any difference?

If lightning is forecast in your area unplugging the sets (mains and antenna/cable) would seem the safest action ?.

[goontron]

Re: lightning rods

one bit of advice i always live by: "Ground your antenna when not in use!"
even indirect strikes can cause enough voltage to kill things.
i have a switchboard that uses RCA jacks, one to my Yamaha, one to my TV, one to my Panasonic RF-3100, one to ground. i had it grounded when lightning struck the light pole down the street and the strike dispersed enough current to weld the RCA plug to the socket and make the wire smoke.

[momaka]

Re: lightning rods

One question might be was the damage caused by the lightning or by a surge in the mains voltage?

It is usually the former that causes the damage. Whenever a lighning strikes, 1000's of Amps can get discharged in a vey short amount of time (i.e. large di/dt). This can induce substancial currents and corresponding voltages in any nearby conductors. So any non-ferrous, non-shielded wires (i.e. from the mouse, keyboard, ethernet, speakers, etc.) will act like little antennas and pick up current (think of this as a large, open-air, "core-less" transformer). If the lightning struck fairly close, those induced voltages and currents can be large enough to do damage.

Also, for this reason, lightning rods and their grounding wires should be routed as far away as possible from any house wiring. And most definitely avoid running the grounding wire for the lightning rod parallel to any other wires.

[Poor Flick]

Re: lightning rods

Wow, everyone! Thank You! I've been reading up on the links and putting that together with your advice. I'm coming to the conclusion this is going to be one of those projects where lack of knowledge could be a very dangerous thing. I'm going to study on this further before I just go and put up some air terminals, cables and ground rods. For now I think I'll look into some whole house surge protection to go with my plug in protection at my tv etc. I'm thinking now the damage came through the cable line as the main and logic boards on the tv were damaged and my surge protector, Acoustic Research 3420 joule, 65 db seems fine. Although, the small kitchen flip down tv, also on cable, had a damaged switching power adapter. I also seen after the incident where one of the two house ground leads that the tv cable ground was attached to was broken loose from its ground rod, even though they both are connected to the same bar in my electrical panel. It also seems to me a high quality lightning rod system won't be cheap at all, so if I'm to do it right I'll need to save up a bit. After more studying, I'll revive this thread with more questions for you all.
Thanks again!

[goontron]

Re: lightning rods

Wow, everyone! Thank You! I've been reading up on the links and putting that together with your advice. I'm coming to the conclusion this is going to be one of those projects where lack of knowledge could be a very dangerous thing. I'm going to study on this further before I just go and put up some air terminals, cables and ground rods. For now I think I'll look into some whole house surge protection to go with my plug in protection at my tv etc. I'm thinking now the damage came through the cable line as the main and logic boards on the tv were damaged and my surge protector, Acoustic Research 3420 joule, 65 db seems fine. Although, the small kitchen flip down tv, also on cable, had a damaged switching power adapter. I also seen after the incident where one of the two house ground leads that the tv cable ground was attached to was broken loose from its ground rod, even though they both are connected to the same bar in my electrical panel. It also seems to me a high quality lightning rod system won't be cheap at all, so if I'm to do it right I'll need to save up a bit. After more studying, I'll revive this thread with more questions for you all.
Thanks again!

yes, put up ground rods so my poor little longwire antenna won't get blasted!

[momaka]

Re: lightning rods

I'm coming to the conclusion this is going to be one of those projects where lack of knowledge could be a very dangerous thing.

Indeed, that is what our professor told us as well (in one of my classes, we had a brief chapter on noise generation, prevention, ESD, and other similar circuit design concerns). He said, this stuff is best left to professionals with experience, and he is the type of teacher that always encourages DIY and related discussions.

[Poor Flick]

Re: lightning rods

Hmm, I'll need to save up even more then.
In regards to the word professional!

[tester272001]

Re: lightning rods

One thing to consider regarding your electronic equipment that got HIT. Do you know the hit came from antenna ? I have seen lightning enter in the AC Mains more often and the GROUND at the service entrance panel is more important for that situation. If your hits were not via the AIR (antenna) and cam in on the AC lines then a whole home surge suppressor (from a home center) is a great thing to have. Will help protect against the Utility company surges as well as lightning flash over hits. Good luck.

[redwire]

Re: lightning rods

Dr. Nikola Tesla's lightning arrestor patent is interesting, because he was against Benjamin Franklin's approach- to attract the lightning via a pointed rod.
Tesla said it's better to repel the strike, push it away from a building. That man was the King of Lightning IMHO.

If your soil is low (geological) conductivity, i.e. igneous rock, then popular grounding solutions are pretty much useless.
If this is your case, I've seen conductive concrete used to make a huge star-ground. Substations also suffer and use resistors to reference the (floating) Wye ground. It's another reason to get a professional to survey the site.