Lighting Rods without ground wire....hazard or not?
Our Museum has a late 1800's 2 story house which, going by old pictures, had lighting rods in the past.
There were 3 that I could see, one on each gable end and one on the "Witches Cap" .
I have 3 antique rods from a tear down and was considering to mount them in those locations. I did not plan to run any ground wire down to the earth. These would be for asteties only.
The entire structure is wood with asphalt shingles.
Would this attract lighting that had nowhere to go?
Comments
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If it's not connected to earth I couldn't imagine them having any effect at all.
On the other hand, I do have a 6" B vent sticking out of my roof 3 feet that is connected to earth. That has made me think a few times.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Doing what you suggest will certainly increase the hazard of lightning striking the house and starting a fire. The rods will increase the height of the structure, making it more likely to attract lightning. Without a low resistance path to ground, the current will flow through the structure.
If you install them, run properly sized and connected grounding conductors and ground rods. Unfortunately that will not be cheap.—
Bburd
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On the contrary — they will attract lightning, grounded or not. It's not just the height of the object, but the sharpness — and lightning rods are made with a small radius tip. And they are, so far as initiating a strike, grounded. Wood is a pretty good insulator, but there is very little current involved most of the time, so the voltage on the rod is pretty much the same as ground. Now of course when lightning strikes, the current immediately becomes insanely high and the wood heats… and the fire department shows up…
Consider. Trees get struck by lightning!
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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I agree that lightning rods need to be grounded to work. By work, I mean conduct a lightning strike safely to ground. But I am troubled by my neighbor's experience. He had a plastic satellite dish mounted to the outside of his house on the second floor. The dish was grounded to a spigot but the spigot's and the house' water supply pipe were PEX, so, the dish was ungrounded when lightning hit it. It sent his daughter to the ER with a burn mark on her back (she was sitting in bed with her back against the wall where the dish was mounted), and fried every wire, appliance, and metal porch railings in the house. It also set the attic above on fire. So, I think an ungrounded lightning rod can be dangerous.
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The tree is wet and connected to Earth.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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@Erin Holohan Haskell I need a different reaction button for this. Something between awesome. Horrified and insightful.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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And the house is wet and connected to the earth also.
The roof (any roof) has metal drip edge on the gable ends, the roof edge has a metal drip edge where the shingles end.
In the old days rather than shingle ridge caps, there used to be a metal cap going the length of the roof ridge, often with a 2" or so decorative ball on each end.
Static roof vents/louvers are metal. Power roof vents are certainly grounded.
Would a wire radio antenna strung inside the length of the attic be the same attraction as the old school antenna wire mounted on the roof? Or the UHF TV antenna mounted in the attic?
Lighting is a fascinating item, I consider it being able to do whatever it wants.
This structure is a couple hundred feet from a metal cell tower which is taller than the house. You can be sure that tower is grounded and should take the strike……but it goes where it wants to.
I often contemplated why houses in town are seldom hit by strikes and lone country houses seem to get hit. I believe it is because of power lines that are taller than the house, they lose lighting arrestors on a regular basis. I witnessed a strike drill into a pile of freshly ground hay just 500' from my house. There were 50' grain bins and power lines around this……why pick on the pile of hay?
Also we have a 130' tall water tower that is all steel and certainly grounded, could it be taking the hits? Or is it passively draining the cloud charge as it builds up overhead?
Now I am in a conundrum, either do nothing or change the copper pipe to CPVC.
I would like to get these things out of my storage unit. 😉
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Arborist compananies ( tree cutters) offer lightning rods for trees. I had them quote a system for my pecan tree but it was more than I wanted to spend.
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braided aluminum lightning rod cable goes forabout $1.65/ft. Cheap, considering….
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I suppose but in general the lumber should be very dry. If it's wet then you need some roof repairs.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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So would the house, with similar results. Run the wire.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
I think everyone missed my point.
The tree is literally soaking wet on the inside.
If your house is this way you have a big problem. I didn't mean just the outside was wet.
I'm not saying there's not an issue, apparently there is. But my point wasn't the tree being wet on the surface.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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It is highly unlikely I will spring for the grounding electrode wire.
I know of only one "modern" house built that got lighting rods, that was in 1979…..I think there was a good salesman involved. Not that they are a scram at all, just got this homeowner to pay for the install…….his house has not been struck BTY.
These rods I have do have the pretty blue glass globes to decorate the installation.
Some thought those were necessary for function but I do believe they are ornamental only.
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At 50,000A, the tree being wet inside doesn't make much difference. The plasma carries the current.
I'd hate to have the OP install them ungrounded, get a strike and the liability.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
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Is the rod continuous through the glass ball?
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
Doesn't have to be. Remember that until the strike actually fires, you are dealing with static electricity. There is no current flowing, and so the conductivity of the objects is irrelevant. Usually the earth — and everything attached to it — is charged up in one direction, usually an excess of electrons, while the clouds above are charged in the other. The voltage difference between the clouds and the ground can be very high — high tens of thousands of volts — but you don't notice it, as you aren't tall enough to sense any difference to speak of (and, in any event, you are a good conductor, which air isn't). In the case of those glass balls, if the rod isn't continuous, there will be a large voltage difference — hundreds of volts — between the ends of the rods — but, oddly, the charge at the tip will be very similar to the charge on the ground. Now eventually the field strength of the charge difference becomes large enough locally to overcome the resistance of the air. The field strength (volts per foot) is greatest at sharp corners or points. Remember up until that moment there is no current flowing, so the resistivity of the material is quite irrelevant. However, at the moment the resistance is overcome, an arc forms between the particular point on the ground and an area in the cloud, and that arc is very conductive — and so a huge current can and will flow — again, tens of thousands of amperes. It doesn't last long — just long enough to temporarily equalize the charge between the ground and the cloud (milliseconds to seconds, never longer). But the heat in the arc is enough to pretty much vapourize anything in the path of the arc, and the residual heat is enough to set anything flammable — such as a house — on fire. If the object is wet inside, such as the outer bark of a tree, it will also turn all that water into steam, and the tree will quite literally explode along the path of the current.
Oddly enough, about the safest place to be is inside a metal box or cage — the current will flow through the metal preferentially, and while you will be deafened and, possibly, a bit perturbed, you will be in pretty good shape. Examples include inside a car with the doors closed, or in an airplane.
A very poor place to be is out standing in open country… or worse, on a hill or mountain!
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
So aluminum siding is beneficial?
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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I certainly don't claim to be an expert on this.
I can't see a ground rod attracting lighting if it is not grounded. If the building was masonry it would be different.
Seems to me lighting goes from cloud to ground or ground to cloud it is a difference of protentional. I feel grounded grounding rods are used where a building is located in an area more susceptible to lighting strikes
But let's say a ungrounded ground rod is on a building, and it takes a strike.
Could the arc jump from the ground rod to a nearby CI plumbing stack which goes to earth? Or to some nearby metallic wiring like BX or EMT, or a nearby metal water line?
There is no material that is a perfect conductor and there is no material that is a perfect insulator. Oil burner electrodes jump an air gap at 10000 volts only a 1/4" gap but the point is a high enough voltage will jump across anything
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The point (oops… sorry) about the pointed rod (or tree branch… TV antenna… umbrella tip…) is that a higher potential gradient exists around it, and that is what makes the arc to strike there than somewhere else.
There's a reason burner electrodes are somewhat pointy…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
Burner electrodes too make a complete circuit, one isn't floating in the air disconnected.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Oh, "go fly a kite"…in a storm, with a metal key on the end of the kite-string, in a glass jar.
See what happens.
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I read on the internet (so it must be true) that, aside from the points of the electrodes, the purpose of the lightning rods and cabling is to bring the electrical potential of the building as a whole down to the same as the earth, thus making the building less 'noticeable' to the lightning when it looks for a good place to strike.
A lightning strike an eight of a mile away blew out my brothers cable modem, router, access point, DVD player, projector, and the HDMI port that fed the projector; but not the switches (3-4) or computers (10+). Lightning does what it wants!
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I had a guy with a PhD in electrical engineering tell me that about lightning rods, or something similar.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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I think the issue with a nearby lightning strike and telecom cables is you can get massive induced voltages from the current of the lightning strike in the ground. Once this gets to your domestic equipment it finds a way to you house earth blowing all sorts of thing up. The voltage is common-mode so it is both conductors to ground.
Ethernet devices have isolating transformers on the data lines so that is probably why that kit did survive. Old fashioned POTS telephone lines at exchange (switches in the USA) have gas surge arresters that grounded the two phones lines. The solution is a lightning arrester on you incoming phone and data service if they are copper. Something like below would work but not cheap!
John
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Thanks to all for your input. I am surprised at the interest in this subject.
So I will most likely not install the "dummy" rods on the house. If it did take a hit and someone sees that the conductors are not connected…… it is a bad look for a 50 year licensed electrical contractor.
The house is not insured as far as property coverage, only liability. However I hold liability insurance for business.
The "Witches Cap" roof peak was lowered by several feet sometime in the past. I wonder if it did take a lighting strike and never got rebuild up to the original height. We have pictures from various stages in it's life.
It was moved across town to the Museum campus about 20 years ago. My grandparents brought it in 1946, so I have some family ties to the house.
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Popular Electronics magazine had a lightning article for radio users 30 years ago which is linked below. It is not directly on point but is interesting.
https://archive.org/details/PopularElectronics199405/page/n39/mode/2up
In my area, a builder and the electronics store employee told me that local houses don't typically have lightning rods installed; they said they are more popular in other areas. I don't know how true that is. Your local fire department and/or city hall engineering departments might have recommendations.
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Hi @JUGHNE, There was another discussion about well pump wiring and how it leaks current and goes bad. I wonder if a local well driller has some old coils of wire lying around that could be used as an inexpensive way of grounding your lightning rods? 🤔
Yours, Larry
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All true, thanks Jamie, but I was just thinking that if the rod is not continuous, the attachment point for the wire should be above the ball.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
The conductivity of the house is more than that of the air, it is lower resistance even if it is dry.
There are numerous things that are even more conductive within the house to help make it even lower resistance.
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When I was working at the Evans Area of Fort Monmouth, New Jersey this happened twice. When lightning struck nearby it induced an overvoltage in all the RS-232C lines blowing out the interface chips.
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Why I ran fiber optic between the garage and house.
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how many feet of cable would you need? The ones around here (Virginia) seem to have copper ground cables. Someone mentioned using aluminum cable; would you have to go up 1-2 sizes?
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Probably wouldn't need to. The cable — whatever it is — is going to be toast anyway. It's just there to establish the initial path of the current. You're looking at thousands of amperes…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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Is it only thousands?
We had a TV hit via the antenna back in the early 90s and all of the copper from the PCB was flashed onto the plastic bottom of the TV. Ok maybe not all but an awful lot.
I don't even know how do you do that.....
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Had lighting strike one of the trees next to my home growing up. Fried the tuner in my TV, had to use a VCR after that. And every CRT in the house needed to be degaussed. O.o ohhh pretty rainbow.
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Aircraft get struck by lightning all the time and they are not grounded. We used to be told to take off our wrist watches if caught in a storm. That may not have made a difference, but I assume we were warned for a reason.
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Just out of curiosity I watched a Utube of installation, This Old House presentation.
The main conductor was run the length of the attic, stapled up at the top ridge board.
Then holes drilled in the roof with threaded studs stuck up that were bolted to the cable and air terminal rods screwed into them on the roof side……serious copper stranded cable maybe #1 or 2.
Then cable run out the soffit down the wall to ground rod. No cable showing other than the drops to ground rods.
Looked to be a clean installation from the street……but doesn't have the charm of old school lighting rods, which would look out of place on a modern 1 story ranch.
However, I have visions of that copper becoming glowing red hot for a second or two and starting the attic framing on fire. 😯
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From my research, ideally, the lightning rod bleeds of positive ions from the surrounding atmosphere to ground, reducing the odds of an actual strike but as we all know, lightning is unpredictable. We have over a hundred rods on our roof. Every exhaust fan , solar panel, and roof edges has a rod. The rods on the edges are spaced @15' around the perimeter and the cables lay across a TPO membrane roof like a spider web. I cannot see evidence of ever being struck by lightning. We get plenty of lightning storms rolling through.
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Glowing red hot is an understatement. It will vapourize almost instantly, and set anything wooden nearby on fire. NOT what you want in the attic…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1
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