With todays electrical grounding systems, i dont believe it's much of a concern, with the exception of mounting un- grounded antennas such as a ham radio operator.

We installed a stainless steel standing seam roof on an old house in the beacon hill area of boston.The reason for using stainless for the roof, besides the longevity, was that it was being used as a ground plain for his radio set up and he had to come up with a radical grounding system for lightning strike prevention.

You don't prevent lightning strikes. All lightning is doing is trying to find a place to ground. It's damage is caused when the strike is going through whatever is in its path to get to ground (usually earth ground). What lightning rods, air terminals, etc are doing is giving a easier path to ground. It isn't preventing the strike, but giving it a more desirable path - rather than through your house to the nearest copper pipe, it follows the air terminal to the copper braided wire down to earth ground.

In terms of safety, since you essentially have an electrical grid running around you with the wiring/piping/ducting in a house, generally a house is considered pretty safe as once it hits something electrical, it'll hopefully go that way. Unfortunately it can cause a lot of damage (electrical, physical, etc) along the way until it finds its path to ground.

Is it necessary ? Well, houses still get hit and cause lots of electrical damage. I know of two houses that were hit with lightning in the last 5 years that burned down.

Is it common ? No.
Is it something that is money well spent ? Depends on how you look at it. Human safety for that freak chance ?

I always thought the point of lighting rods is that the pointed rod discharges the potential gradient before it reaches the breakdown potential of the air, preventing a lightning strike in that immediate area.

Did I get that wrong, and the lightning protection system is actually trying to attract a strike, as Anthem wrote?

Back in the good old days lightning rods were marketed by people who couldn't make it as snake oil salesmen. The fact that Ben Franklin invented them seemed to bolster their marketability. Back in Ben's day little of what made up a house was metallic in nature (and certainly none of it was a continuous path to ground) so maybe it made sense then.

All sorts of good stuff at the attached site which appears to be reasonably scientific in their assessment.

Here is a link that might be useful: Lightning Rod Article

A lighting protection system isn't actually 'attracting' a strike. Lighting is going to go where its going to go. The 'strike' when it happens is going to find ground and nothing is going to stop it. When a tree is hit, its the strike going through the tree to find ground(the tree got in the way, it wasn't the final destination).

Any successful lightning system is generally installed higher than the structure it is going to protect and offers a more 'attractive' path to ground than hopefully something else (namely the physical structure of your house). It isn't any more attractive or less attractive - it's just if it decides to hit, it'll hopefully take the path to ground rather than blowing a hole through the side of the house and hitting something else to ground (usually the combination of pipes, electrical wires, ducting, etc and thereby electrifying the rest of the metal objects in your house).

If 'metal' was more attractive than the rest then people with standing seam metal roofs would be hit all the time (which isn't the case). A potentially successful (and nothing is foolproof) has certain ratio's in terms of height above the roof, spacing, number, type, etc for air terminals, down conductors, grounding etc that all need to work together to give you a hopefully effective solution.

That link to NLSI is actually very good reading for people considering lighting protection. I would just click on the entire contents and read through that rather than the particular section that the one small opinion piece.

Here is a link that might be useful: Entire Lightning Protection Information

I looked into this after 1) lightning struck the transformer on the power pole that feeds our house and fried our garage door opener and central vacuum cleaner, 2) a tree behind us was struck and died about a year later, and 3) a $600K house nearby was struck and burned to the ground in about 20 minutes. I decided fate was trying to tell us something by zapping everythign around us - we are on top of the hill and are by far and away the tallest thing around. In the end, I decided that lightning rods weren't going to provide enough protection to ensure that my house, if struck, wouldn't be seriously fried anyhow. I did, however, have an electrician install a whole house surge suppressor and a lightning arrestor, which, from what I understand, is simply a big surge absorber with its own direct ground. I'm not sure how much good either one will do in case of a direct strike, but hopefully it will protect our appliances from further surges when things nearby are struck. Getting both installed ran about $250 or thereabouts, IIRC. I'd imagine it would be even cheaper to put on during the initial wiring, as ours was a retrofit.

Actually the whole house surge suppressor does nothing to help a lightning strike on/through your house. What you've probably installed is a MOV based surge arrestor which means that surge coming through the line will get damped and taken down. So, yes if the strike hits your on-pole transformer it will more than likely minimize the damage to your appliances. However, that case of a house being struck near you and burned down - well, the MOV does nothing for that because you aren't giving the strike an easier path to ground. it will still blow through whatever it is going to go through (trees, houses, etc) until it finds ground.

A lot of houses burn down with a lightning strike for whatever reason. Not sure if its the lightning causing the fire or the resultant electrical charge frying everything in its path, but it is an issue when a strike happens.

I think people need to understand that it isn't a lightning rod that gives protection. Get a qualified study and get some decent information. I don't see how you can decide that 'lightning rods weren't going to provide enough protection to ensure" your house wouldn't be fried, yet believing that a MOV sink will ??? The 'rods' or air terminals are above the roof line and tied together to down conductors to ground. The question is whether the installer engineered it such that its adequately installed so that the coverage attracts a strike to go that route vs another - not whether it works or not.

Now whether you want to pay for it, can afford to pay for it or don't want to pay for it can certainly factor into whether one installs it and I can understand that. But to say that installing a MOV sink will protect yourself over a lightning protection system is a bit absurd. (BTW, an adquate LPS contains a MOV sink as well, but its the other components tied into protecting the entire house) The other components are potential lifesavers as it protects the building- the mov sink only protects the powered items within the building.

I don't think the lightning arrestor and/or whole house surge is going to save me from a direct hit. Nothing will, I suspect - if lightning hits my roof, I fully expect my house to go up in flames just as the one nearby did. But I hope to minimize the toasting of my appliances and electronics should lightning hit the pole or a nearby tree.

The cost of a lightning rod system for my house was around a thousand bucks (plus I'd have to find someone to install it and no one around here does that kind of thing) and involved putting lightning rods about every 6 feet across the peak of the roof and cables that ran down the sides of the house into the ground. It was expensive, butt-ugly, and could offer no guarantees that if lightning struck, my house wouldn't burn down. Didn't seem worth it to me. The surge suppressor and lightning arrestor (they are two different components) were cheap and offered protection against a nearby strike or power surge, something that is much more likely to happen than a direct hit to my house (knock on wood!)

"I don't think the lightning arrestor and/or whole house surge is going to save me from a direct hit. Nothing will, I suspect - if lightning hits my roof, I fully expect my house to go up in flames just as the one nearby did."

And that is where I think you are mistaken. A well designed LPS system on that roof, will more than likely take the hit when lightning does strike your house. It will take the most favorable path down to ground. I've seen when lightning systems have been hit and who knows what would have happened if it wasn't taken to ground. So yes, they do work. And while there are no guarantees, the alternatives aren't any better.

I'm not saying its foolhardy to not put a system in as they are costly and playing the odds of lightning hitting your particular house are very slim. What I /am/ saying is that I think you're incorrect in saying that a lightning arrestor/surge suppressor is an adequate substitute. I'm also saying that your feeling that your house would burn down because nothing will help it when lightning strikes is also probably wrong. No guarantees as no one can guarantee these things, but there have been enough occurences of LPS systems working that the best practices are actually pretty good in that field.

I have two friends who have had oak trees in their yards struck by lightning, and both trees were within 50 feet of the homes. Both oaks had taller pine trees within 200 feet of them.

I was considering fashioning a flag pole that doubled as a lightning rod, some distance from my house, but it seems lightning doesn't start looking for it's final path until pretty close to the ground, or have I got it all wrong?

Lightning has a tendency to strike near the same area for whatever reason. A flag pole could conceivably help if on top of the structure you are trying to protect and sufficiently high enough, but the problem is that lightning is a result of cloud to ground strikes. The leaders that keep working their way down are anywhere from 50-150ft long. Which is why when you see air terminals, they are usually spaced only 10-15ft apart for coverage. What that means is that even if you had one pole 10 ft higher than the rest, a cloud to ground strike could happen 20 ft away rather than right on your pole. . .

But yes, you are correct that lightning doesn't really 'look' for its final path. It just gets nearer and nearer to the ground as the different charge groups start getting closer (earth and the charged cloud) until it finds the best path to ground.

In your earlier example, the oaks werent the target point. As the lightning gets closer to ground, it was going to hit somewhere near the tree and the tree just happened to be in its path and got hit (that and the tallest thing doesn't always get hit).

I have a lovely old barn about a quarter mile away from the new house.

It was hit [for the first time in its hundred year life] a couple of years ago. Blew the tin weather vane off the top, then a line of shingles about a foot wide down the roof [not a perfectly straight line, either], then shattered a couple of the vertical siding board on its way to the ground...

I really don't want a lot of spikes and shiney cables all over the roof, since I'm going for a rustic sort of look, but I think the geography of the area may demand it. The plumbing in the new house is PEX, so that won't provide a ground path, the shingles are fiberglass and the electric is underground for more than a mile. The house is the tallest thing for several miles in every direction except one: the ground rises to the west. The hill back there is still several hundred yards away, though, so probably useless in terms of the current discussion.