Lightning Rods

[leilanidude]

Ther higher the "joules" rating is, the better the protection.

[kalakoa]

a 10' steel pole. Is this a lightning rod?

Mitigate the potential lightning strike by providing a path of least resistance, such as a solid #6 copper ground wire that runs directly from the pole to a ground rod.

The best protection devices typically include some "gas discharge tubes". Which probably means making them yourself, because commodity "surge supressor" doesn't include these.

[kimo wires]

The lightning damage I've seen on homes occurs from lightning entering through the grounding system, through a nearby ground or tree strike, It then exits at a random spot anywhere in the house. It could be on a conductor as big as #6 stove wire or as small as a 20gauge phone wire. A metal roof is better than shingles. The metal will dissipate the charge over the entire span. But Wet shingles won't. That's why when lightening hits a wet shingle roof it blows a hole in it.

[geochem]

TomK is correct: a TV antenna cable would likely vaporize leaving the current looking for another path to ground. The "problem" is related to current and resistance - Hunt's analogy of turning on a 2200 kw light bulb isn't quite correct: that light bulb is passing current through a resistor, not a conductor. The purpose of the heavy copper wire (I've seen braided heavy gauge wire ~1/2 inch in diameter used) is to allow that instantaneous current to pass while generating minimal heat. Same problem with MarkD's analogy: (the moisture in) trees can conduct, but it isn't a good conductor and will vaporize (hence the explosions) due to that heat.

I would guess that equally important to the diameter of the copper wire, would be the adequacy of the grounding in Puna's rocky ground - rocks aren't good conductors, and even wet rocks are only fair. So proper grounding of the lightening rod would likely require running buried cables across the yard to ensure that the charge cold be dissipated effectively.

[MarkP]

According to the internet there is a parameter called the fusing current at which the conductor will melt like a fuse. For 0000 copper wire, which is about as big as your thumb, I found the value of 30,000 amps, so half of lighting strikes would melt it like a fuse. OTOH half of the time such a conductor would actually conduct the lightning bolt and presumably save your house from further damage, at least the physical structure of your house. I can't imagine that any electronics nearby would fare very well. The principle of a transformer is to induce a voltage in one wire by placing it in close proximity to another wire that is carrying a rapidly changing current. Your whole house would be a transformer. The spoon in your hand while sitting at the table on the other side of the house from the lightning rod and conductor would probably give you a shock.

If I understand correctly a lot of the damage to electronics comes from being connected to the grounding system of the house wiring. That grounding system serves a good purpose under normal circumstances but all bets are off if your house gets hit by lightning.

[Hunt Stoddard]

Not to beat a dead horse on this issue, but again, it gets back to whether having a lightning rod, or even grounding your metal roof is actually advisable or not. If lightning hits an ungrounded metal roof we can assume that it then disperses to various paths to ground, one of which might be through you, which is bad. If the roof is grounded the lightning "decides" to follow the grounding conductor. For the most part. In fact, it will still follow every available path, according to the parallel current law. It's just that most of it will go down the lightning conductor to ground.

But wait a minute. By the same token, lightning in the atmosphere will "go through" (i.e. strike) your house to the extent that it serves as a good conductor to ground, which you have just made possible with your excellent lightning rod installation. Doesn't really make sense.

[TomK]

Hunt - personally, if I were to install a lightning rod on my property, I wouldn't have it attached to the house. That makes things complicated of course and probably more expensive, but I would want it a few dozen yards away.

[Seeb]

I have seen flag pole lighting rod setups that reportedly work- they are supposed to protect a 45 degree cone down from the top of the pole. They need an actual ground tho not just stuck in a rock

[sistersue]

Maybe you should study what the people in Florida do about lightning. I think that's the "lightning capitol" of the USA?

[Hunt Stoddard]

quote:

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Originally posted by TomK

Hunt - personally, if I were to install a lightning rod on my property, I wouldn't have it attached to the house. That makes things complicated of course and probably more expensive, but I would want it a few dozen yards away.

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That would be my preference. Get it away from your house.