Image Credit: Image #1: Lynch - Flickr.com
More Musings of an Energy Nerd
Recently, lightning struck near the garage and house of good friends of mine, a Vermont couple named Susan and Stan. Lightning destroyed a tree, fried all of the electronics and some of the electrical wiring in both of their cars (parked outdoors), and damaged electrical wiring and equipment in their house.
Fortunately, their home didn’t catch fire, but their cars were apparently totaled, and the house was rendered temporarily unusable. As they await electrical repairs, they have taken shelter in a friend’s house, and are now driving rental cars.
I asked Susan what happened. “In the early morning, we could hear thunder from our bedroom. At 5 a.m. I heard an explosion — a boom — so I got up, looked outside, and noticed that a tree had been severed. The top of the tree was stuck in the ground three feet from its trunk. I saw all this debris in the driveway and dirt all over the cars. I thought that lightning had hit the tree, but I was really tired, so I went back to sleep.
“An hour later, at 6, Stan got up and looked outside. He noticed that the rear-view mirror of his car was blown apart. One of his tires had exploded, and there was a rut that had been excavated into the ground. There there was debris and dirt all over. We knew it was lightning.
“Then Stan noticed that there was a hole in the garage. There had been a metal ladder leaning on the garage — we had been staining the siding — and the lightning must have hit the metal ladder. It blew a hole through the clapboards. The clapboards were destroyed. All the lightbulbs in the garage were exploded. The garage door openers had exploded. There were electrical wires that were severed.
“Both…
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9 Comments
Every lightning bolt has an amazing amount of energy. Should you take a direct hit as your friends did almost no system will save you from at least some damage. I agree that set of lightning rod are generally unlikely to prevent enough damage to recoup their cost.
What is much more likely is the wires that feed electricity, phone service and cable TV to your home take a lightning hit and the wire carry some small part of the lightning strike into your home and damage something. Our high performance homes generally rely on sensitive electronic to work like the variable speed motors in our HVAC system, induction cook tops and HP water heaters. I feel that whole house surge suppressers are a necessity today and a good investment.
Walta
https://www.homedepot.com/p/Eaton-Whole-House-Surge-Protector-CHSPT2ULTRA-1/204761136?cm_mmc=Shopping%7CG%7CBase%7CD27E%7C27-8_CIRCUIT_PROTECT._DEVICES%7CNA%7CPLA%7c71700000034238981%7c58700003943782709%7c92700031956831781&gclid=Cj0KCQjw77TbBRDtARIsAC4l83kkR2DyNDuPeyK6Rpcg8NuLKreijUmHUGvM0QY74vXvM8NEWZJuDtcaAuLtEALw_wcB&dclid=CImhjcr_4twCFVCoaQod5v0EIQ
I know so little about this, my questions are more basic.
Leaving aside whether they work, is the idea behind installing rods that they will attract the lightening to hit them, rather than other nearby high points? That is, are they actively trying to get the lightening to hit them, and if so why would the lightening choose to do so rather than say the roof nearby?
- Are the cables grounding the rods able to take the voltage a strike feeds through them, or just mitigate some of the potential damage?
- Given that the damage to Martin's neighbours property seems to have been from electricity moving through the ground once it had hit the tree, is it sensible to believe that simply directing the current to the ground solves much?
Malcolm,
Good questions -- and I'm not the best person to answer them.
A lightning protection system is basically a ground (along with a low-resistance conductor to the ground). Atmospheric electrical discharges sometimes happen near a building, and when one does, providing a low-resistance path to ground is better than providing a high-resistance path to ground (for example, through a tree or through your chimney), because a high-resistance path results in heat and more ancillary damage. That's my understanding, anyway. Expressing it the way I just did is a little different from saying that a lightning rod "attracts" lightning.
If lightning passes through a lightning rod via a copper cable to a grounding rod, can the building with the lightning rod still be damaged? To the best of my knowledge, the answer is yes. The hope is -- and there is some evidence to support this hope -- that if the building is damaged, the damage will be less than it would have been without the lighting rod and ground.
My cabin will sit on an exposed hill and the roof height is close to 30'. I think I can put four rods on my standing seam metal roof, tie them together with braided copper line, and connect to a couple of ground rods for around $500. I have no idea whether it's a necessary expense but if it provides some illusory piece of mind, it's probably worth it to me.
Martin,
Thanks for the reply. It all academic for me, as we get lots of rain but no lightening here.
While in college I recall visiting a AM radio station in Texas where a classmate was working. He showed me the antenna, something like a 100 foot tower of steel, and pointed out some lightning protection (of which I don't remember details) because certainly if anything is a target for lightning, it would be a metallic tower sticking into the sky.
A house is not nearly as tall and less likely to be hit but I would imagine the odds are increased if there is metal roofing, metal siding, and/or metal plumbing vent pipes. Perhaps metal ducts and vents through the roof also increase being a target, maybe depending on how well they are actually connected to the ground.
And then there are power lines and fences that often get struck. Power lines can bring a surge of several thousand volts into the house. I've read that wall outlets generally limit the voltage to somewhere less than 10,000V above which it will arc across the contacts instead. Certainly not a voltage to sneeze at.
I don't think anything will protect against a direct strike, but I am getting a whole house surge protector installed on my new home. Certainly helps your odds for "near miss" strikes which are way more frequent. Actual electronics are important, but since you can't seem to purchase an appliance without an electronic touch screen these days, your blown flat screen tv might be a drop in the bucket compared to changing out all the control panels on your main appliances in case of a large surge(furnace/water heater/stove/refrigerator/washer /dryer etc.)
If you're building the place new, a couple hundred and you've got it. Also, it may not be the home that endures the cost, but the electronics in it. I'm building an off grid home with batteries and solar etc. A lightning strike will be more than a nuisance for me, so a couple of lightning rods and some 6 gauge wire it worth it.
I'm hardly an expert here, but my understanding is that the lightning rods effectively make the roof the lightning equivalent of the ground: the high-capacity, direct path from the lightning rods to the ground around the house make it seem like the whole house is at ground level rather than raised above the ground. It's not so much about the rods attracting lightning, but about creating a protective 'bubble' around your house. Or so the proponents would say at least.
I had a bad lightning hit at our house in NH back in 2015. I had all of the normal protections -- whole house surge suppressor, quality power strips with surge suppression, etc. -- and, although they potentially helped, I still ended up with a lot of damage. Structurally, the only issue was a bunch of plaster that exploded away from the wall where we were hit. Electrically, I lost about half of the low voltage devices in the house including a well pump controller, a bunch of Ethernet switches, a ton of thermostats, etc. There wasn't much damage to the 120V electrical, but the lightning seemed to flow down a lot of my low voltage wiring destroying a number of systems in its path.
I installed lightning rods after that -- along with a new roof that was overdue anyway -- and haven't had any lightning strikes since then, but... who knows if it really helped. For $20K in damage, though, it seemed like a reasonable protective investment against future strikes. (We are at the top of a mountain and very exposed so, although NH isn't known for being lightning-prone, we get more strikes than most in the state.)
Anyhow...
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