Lighting Rods without ground wire....hazard or not?

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.

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!

The tree is wet and connected to Earth.

braided aluminum lightning rod cable goes forabout $1.65/ft. Cheap, considering….

So would the house, with similar results. Run the wire.

@JUGHNE

All that's been said here sounds like leave them off.

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!

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

Burner electrodes too make a complete circuit, one isn't floating in the air disconnected.

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!

@ratio

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!

7TCA085400R0116 ESP 50E | WJ Furse, ESP E Surge Suppressor Unit 58 V Maximum Voltage Rating 5kA Maximum Surge Current Twisted Pair Surge Protector | RS

John

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.

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.

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.

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?

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.....

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.

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.