Lightning Protection: What's the 'last word.'

From time to time, I see or do something that renews my interest in lightning protection. For example, last week I was on my room tending to our TV antenna (it's reasonablly well grounded with #6 Cu wire going to opposite ends of the roof and then to ground rods which are also bonding to the electrical service ground.

Also, last week, I say three trucks of a nearby electrical co-op installing some blunt end rods on top of a series of power poles. The ground wire was below the 3 high voltage phase conductors.

I also glanced at a 100 year old (or so) patent by the great Testla. In the patent, Testla claims that pointed ground rods are a bad idea.

His "best idea" is having a "conducting cap" with rounded edges as the highest part of the structure. The cap would be separated from the grounding system by an "air gap." The idea seems to be that the capitance of the "cap" will let it soak up some charge and reduce the chance of a "streamer" starting a true lighting strike.

So: we have pointed rods, charge dissipators, blund rods, and insulated caps.

Anything else?

What works and what is nonsense?

Reply to
John Gilmer
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Consider that lightening comes from several hundred, if not several thousand feet in the air. In order for it to make that long of a trip, it has to be pretty excited.

So ANY "lightning arrestor" where one hangs a spike on the side of a building only serves to direct and guide the stroke to ground. It never actually carries the body of the current of the stroke. It is meant more so that the stroke doesn't choose the building itself as the path, usually resulting in a fire.

A capacitor meant to grab lightning bolt energy will only be able to keep that which does not flash over to ground during the event. If it can flash from the sky to ground, it can certainly flash around any device or creepage fins or any other thing we have way down here at ground level.

Lightning rods work because the pointed tip creates a huge gradient spike making it the most attractive point to strike when the cloud gets charged up. They also allow one to choose where a strike will be occurring by way of placement selection.

Reply to
life imitates life

"life imitates life" wrote in message news:

It amazes me that all of that voltage can be handled by a #6 wire.

Reply to

No, it can't. That was the point of what I wrote, which you snipped.

All a rod does is attract the strike to a known location, and then giving SOME of the current a path to ground. Note how bare copper is (or should be ) all that is used, and it is on the EXTERIOR of the building. That allows the majority of the stroke to 'follow' the copper down to ground. The wire gets a lot of it, but most of it remains external even to the wire.

Reply to
life imitates life

There is no better protection than the traditional lightning rod (now called an "air terminal"). Or it is practical sometimes to use an elevated grounded wire above what is to be protected (often used by utilities).

There is a lot of good information from the National Lightning Safety Institute at:

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in "5 structural lightning safety"

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a good simple overview.

There is disagreement whether a sharp rod or blunt rod is better. Far as I know there is no evidence one is better than the other.

There are at least a couple schemes that claim better protection than conventional rods.

- Early Streamer Emission (ESE) claims to provide protection over a large area with a single terminal.

- Charge Transfer System (CTS) claims to prevent lightning strikes. The claim is that sharp points will discharge the thundercloud or will create an ion field that will prevent a lightning strike where the device is installed.

There is no reason to believe either device works (other than a conventional lightning rod). NASA and the FAA did not find they worked as claimed. For more information:

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You can ignore Tesla's patent.

Conventional lightning rods provide a "safe" point for lightning to discharge to. They work by being the high point (which, unfortunately, your TV antenna probably is).

The voltage at the rods and along the down conductors may be far above ground potential. Codes may require that metal within 6 feet of downconductors be bonded to the downconductor. If not bonded there may be an arc.

An "average" strike is about 20,000A. Only about 5% of strikes are above


A lightning strike is a very short event, so wires can be smaller than you might imagine. A #6 wire will have about a 50 degree C rise with a

200,000A strike.
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If your antenna is actually struck by lightning you would need more than ordinary protection for equipment attached to the antenna. In particular the antenna lead entry ground block needs to have a short ground wire to the ground at the power service.
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I once saw a rather bizarre description of a type of lightning rod. The rod didn't end at a point but in an almost umbrella-rib like top made of large diameter stranded wires. At the ends the strands were unraveled and sharpened, making lots and lots of corona-generating points. The idea was that lightning would strike one of these things that were around the thing they were protecting, and not the thing itself. It may have gone on beyond that, small diameter stranded wire soldered onto the unravelled ends of the large diameter wire, with its individual component wires unraveled, producing lots of copper "hair", each tip a corona generator.

One of these lightning rods would take the strike before the protected thing came in range, and there was supposed to be no more energy left to strike the protected thing. I don't know if it was a real system or the creation of a mad scientist.

Reply to
Michael Moroney

I think the description of Early Streamer Emission (ESE) systems is umbrella shaped. If it is, they don't work as claimed. There are related cites in my 1st post.

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[Bzzzzzt!] "Yeow!!!!"
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Paul Hovnanian P.E.


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operator jay

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