It's like Ben Franklin with a key and a kite...you see it right?
November 8, 2017 7:35 AM   Subscribe

Suggestions, tips and tricks for attaching (installing?) a lightning rod to my house?

A recent lightning strike and subsequent devastating house fire in the neighborhood has led me to look at lightning rods as a way to mitigate the risk of same at my own place.

Those of you who have done this: how to approach, where to begin, brands, etc etc? I have no idea where to start and would appreciate any and all input. If you have a l. rod, has it ever been struck? Results?

Or are there other measures I can take which will accomplish the same thing? Total n00b here!

Thanks.
posted by Ginesthoi to Home & Garden (8 answers total) 3 users marked this as a favorite
 
Someone more versed in the matter could get you a better answer, but it's not just as simple as buying something and putting it on your roof - for a large facility I worked on where we looked at lightning protection, the system also involved a method of distribution, where the rod was connected to a cable of some sort that surrounded the building, taking any electrical charge into the ground. The grounding is important - you have to give the lightning someplace to go that's not your house. I don't think this is a DIY kind of thing because the cable has to be correctly sized and located.
posted by LionIndex at 7:53 AM on November 8 [2 favorites]


My first call would be to an electrician. They have some relevant expertise (possibly a lot!) and they can order and install the right parts.
posted by Huffy Puffy at 8:05 AM on November 8 [1 favorite]


2nd the electrician.

to the hope that your lightning rod provides, may you always be satisfied.
posted by ovenmitt at 9:15 AM on November 8 [4 favorites]


Roofers or lightning rod companies have the expertise to figure this out. It's not just a rod --- it's a system. Not a DIY situation.
posted by mmf at 9:50 AM on November 8


It actually could be a DIYable thing if you're willing to learn about soil conductivity, electrical theory, etc., and your house's electrical system is properly constructed to modern standards. Problem is that by the time you learn all that, all you may learn is that you need a pro.

And all that said, if your goal is to absolutely ensure you never have any significant damage from a direct lightning strike, you will fail either way. What something you can actually afford to retrofit will do is make it much less likely the whole thing burns down. It (probably) won't save your electronics without a lot of stuff that turns out to be literally impossible in some soil types without a properly designed system being installed during construction.

Somewhere on DSL Reports, a WISP in Missouri documented the process of constructing the grounding/bonding system for a new tower they were putting up. And that's for something akin to what people do with lightning rods. We're talking thermite welded connectors, a loop of very large wire around the tower and building to create a protected "halo," and IIRC even bonding to the rebar in the concrete pad on which the building (and separately, the tower) sat, then making sure that the electric panel ground was bonded to the same grounding system along with all the incoming telecom stuff. In a house, you also have to be able to bond your water/gas pipes (and anything else metal) to the same ground as well.

FWIW, lightning strikes that burn down buildings are very rare (because hitting a house is rare, since they are rarely the tallest thing around) so long as the electrical system is grounded properly and all pipework and telecom cabling are bonded to the same grounding rod. The big problems usually come when that isn't done and different things have different induced voltages on them that can then cause enough current flow to heat up wiring/piping/whatever enough to start a fire.

(I'm not an electrician, just an IT person who has had to clean up the aftermath of more than one lightning strike, direct and indirect, though never one that caused a structure fire, even in hundred year old buildings in rural Arkansas that were built before electric power was a thing)
posted by wierdo at 2:03 PM on November 8


I don't know, it could be a DIY thing. Your aim as a homeowner is somewhat different from that of a WISP. Theirs is to protect very sensitive and very expensive electronic equipment from even relatively minor EMF fluctuations. Yours is to have the lightning hit the neighbor's house instead of your own.

Lightning rods systems do not protect you by channeling the lightning strike past your house and into the ground. They protect you by preventing the strike in the first place, by bleeding electrons from the ground to the air to reduce the differential. If the difference in charge at your house is less than at your neighbor's house, it's highly probable that their house will take the hit. So you don't have to have a perfect ground, it just has to be enough to make you "less attractive" to strikes. If there's a direct hit next door, your electronics are still going to get fried. But your house won't be the one that bursts into flames.

I'm sure there are reputable companies peddling complete systems that can instruct you on how to do it.
posted by bricoleur at 5:25 PM on November 8


Lightning rods systems do not protect you by channeling the lightning strike past your house and into the ground.
Uh, yeah, they do…
They protect you by preventing the strike in the first place, by bleeding electrons from the ground to the air to reduce the differential.
Ol' Ben Franklin may have theorised that, based on what was known & observed at the time of related phenomenon e.g. coronal discharges. But he was wrong.

(If you think about it, if what Ben thought was true then trees - quite good conductors compared to air (especially when wet), large, fairly pointed & often covered with thousands of other sharp points - would be very rarely hit…)

It's true enough that the strike you see is actually ground-to-cloud - but that's preceded by an air-to-ground discharge. Roughly, this is what happens during a lightning storm:
  1. Friction from air/moisture movement within clouds causes them to become negatively charged with respect to everything else, including the ground. In most clouds the potential difference doesn't become high enough to create a discharge; the charge simply bleeds & equalises between cloud and air. But in a lightning cloud, charge production outstrips this ability to equalise charge.
  2. When the charge builds up to a high enough level, an invisible / barely visible 'stepped leader" negative discharge escapes from the base of the cloud through the air & starts creating an ionised path. These can be seen in high-speed photography - they 'strike' forwards a few 10's of metres, seem to pause for a few 10's of ms, then branch & continue on repeating the same pattern.
  3. When one of these negatively-charged branches gets within ~50 metres or so of the ground, it's close enough to attract / be attracted by (opinions differ ;)) the positive charge on the ground. Either way, the 'stepped leader' forms a path to the ground causing higher current to flow, and that path is further ionised.
  4. The positive charge from the ground then suddenly discharges along the ionised path, creating the 'lightning strike' we see.
The purpose of a lightning rod is to (a) lift the positive charge from the ground (& buildings on it) higher than the structure it's mounted on, so that any stepped leaders that come close will hopefully be attracted to it and not the structure, and (b) provide the lowest-possible-impedance path to the ground - via thick cabling, large straps, and, yes, thermite-welded connectors, to a large ground mat surrounding the structure - so that the energy of the strike travels along that path and not through the not-quite-so-low-but still-fairly-low impedance path of the roof/walls/wiring/piping of the structure itself.

That said, having worked alongside the power & lightning protection guys in a previous telco job*, personally I'm not so convinced that lightning rods are typically worth it. Got a large low impedance structure (e.g. tower, unit block, etc.) that stands high above or apart from surrounding trees/structures? Sure, go for it, but it needs to be professionally done - your typical 14ga earth wire & household earth stake / water pipe will last long enough to attract the lightning, before it vapourises & the energy in the strike takes the next-lowest impedance path it can find nearby. Like your house walls, wiring, or piping…

But a typical house, surrounded by trees / other structures of similar height or higher within 50 metres or so? Not really worth it - you'd mostly be increasing your chances of lightning hitting your house, and the electromagnetic discharge itself will induce enough current in surrounding wiring / metalwork to cause related damage whether it hits your house or your neighbour's anyway…

(* I looked after power & building maintenance for the local telco for a while, and those guys knew their stuff. All the towers were fitted with lightning rods, or at least proper earthing all the way up, because they were frequently struck. Lots of the older exhange buildings - 2 or 3 storey house sized, typically on or near the tops of hills - were also fitted with lightning rods, but the newer ones weren't. They used to monitor lightning strikes on all the plant - towers were commonly struck, but there was practically no difference in the likelyhood of a building being struck in a residential area regardless of whether it had lightning rods or not. Damage caused by nearby structure or ground strikes being inducted / conducted into the building through the power / grounding / telecomms cabling? Sure. But unless a building was literally standing in a bare paddock or hillside with nothing else around it, lightning rods made little or no difference to the likelyhood of lightning damage.

Later on, I spent some time doing customer work &, large electrical storms being almost a weekly occurrence here in summer, saw a fair bit of lightning-damaged exchange, external plant, & customer gear. The one example I remember most was a case where the house next door was struck - in the house I attended practically everything electrical was a write-off except an old mains-powered dial wall clock. In the house that was actually struck, everything was fine except for a similar clock that was mounted on the wall directly under where the lightning hit the house.

But I also saw plenty of the opposite…)
posted by Pinback at 12:55 AM on November 9 [2 favorites]


Wow, I had no idea this was such a complicated thing. Thanks to all of you experts with your extensive knowledge.

And a particular tip of the tricorn hat to ovenmitt for making me laugh out loud....well done!
posted by Ginesthoi at 5:11 AM on November 10


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