Lightning

Don Y wrote: ===============

** Antenna groundings is NOT for lightning hits.

It is for electrical safety, preventing the antenna ever becoming live. It also stops static voltage build up - which can reach 10kV in dry, windy conditions.

Lightning rods have to be very substantial copper pipes or bars.

..... Phi

In Germany lightning protection of antennas and often even bare rooftops was required. So when I started ham radio there I read up about their standards. AFAIR the "wire" from the antenna to the ground rod had to be

16mm^2 (!). Huge. It was meant to survived a lightning hit and be able to take another. Just bending that stuff took raw force. You had to do push-ups in the morning to shape up.

There were rules that it could not run horizontal and no sharp angles.

The ground rod was also massive. I forgot but I think the diameter of that was almost 1/2".

Did you mean 16mm in diameter? Because 16mm^2 is only 5mm diameter, and you'd have to be a weakling to find that difficult to bend.

As I understand it, a lightning "conductor" does not typically actually conduct most of the current - it just gives it a starting point to follow. It still has to survive to be useful, of course.

CH

Don Y snipped-for-privacy@foo.invalid wrote in news:sdvl8d$blp$1@dont- email.me:

Wow... like those little feeder dendrites which propagate just before a strike.

Our rooftop antenna got hit back in the seventies and I think our protection was a single 14Ga Copper strand... maybe 12Ga. Down to a true 5 foot driven ground rod. The strike burned a trail along that "low resistance path the wire provided, and a burn through and fire started at the strike point but was extinguished by the rain. We had an Aluminum awning on the back porch of a two story 5 bedroom colonial house. My grandfather was standing against the awning's second stanchion post drinking a pretty big mug of beer. It made him jump about five feet and he almost had a heart attack. It was almost the loudest thing I had ever heard as a kid in Ohio, second to funny cars at the drag strip and train horns up close. It is what took out our Zenith 25" color floor console model from 1963 after 11 years of faithful tube circuit based service. I watched world series' on it and Olympics and the Moon landing and the Monkees and The Twilight Zone and Alfred Hitchcock Presents and Batman and Star Trek and Lost In Space and The Rifleman and Frosty The Snowman, and Rudolph The Red Nosed Reindeer and the Grinch and Scrooge and even JFK's assassination. and Bobby's too. That TV shaped my life back in the days of only 4 or 6 channels.

Anyway... if ya didn't notice, I digress... It was really a fairly small lightning bolt.

I saw ball lightning less than a block away in the seventies too. Two 8 inch translucent red and blue spheres appeared after a bolt struck my bus driver/farmer's barn peak rod. They cascaded down the side of the barn slowly and stpped to hover about 6 feet off the ground and then popped out of this plane of existence into a vacu- flash. All over a period of 3 to 5 seconds.

Can't be too expensive for one strand of wire. I would replace it.

In fact I would buy 12Ga romex and strip the outer sheath off and use the fault return bare strand, and the other two can be stripped and used or used with their NFPA approved jacket still on. That way you have one and two replacements ready and waiting. Or braid all three together and be a little more certain that it would be following your wire as the path to Earth instead of your wet building surfaces. I would put stand offs and make the thing run 2 inches off everything all the way to the lightning rod.

A GDT arrester is inline between my ham radio and antenna.

The GDT datasheet says it can theoretically reset hundreds of times, dependent on the nature of the surge. But the datasheet doesn't describe details of the reset. Wikipedia claims most modern lightening arresters are also "filled with a precision gas mixture, and have a small amount of radioactive material to encourage the gas to ionize when the voltage across the gap reaches a specified level."

Presumably these more robust arresters are also able to reset.

Danke,

A storm was coming up in my neighborhood the other day, and there's a big wild apple tree down the street and the high winds started knocking apples off the tree. Sky was black as pitch. A bunch of kids and some adults ran under it and started grabbing some of the (pretty juicy-looking) green apples and I was watching this from my window thinking about how many Americans I could successfully perform CPR on simultaneously...

The strike will probably take multiple paths to ground. Like a genetically-selective, carefully-raised lab animal subjected to perfectly-calibrated stimuli, it will do whatever the hell it wants :-)

The goal is to divert enough of its current to a relatively safe path, that the remaining current doesn't do irreparable damage to other things.

If the conductor is heavy enough, grounded well enough, routed properly, and bonded well enough, it may survive multiple lightning strokes.

This is not, by any means, guaranteed. It's quite common for such conductors (and their associated grounds and bonds) to fail after one or more lightning strikes. A poor bond between conductor and ground system may very well blow itself apart during the first strike.

Suggestion: download and read this:

This is a copy I found of the U.S. government military handbook on grounding... it has both the theory section (part 1) and the practical- applications section (part 2).

bitrex snipped-for-privacy@example.net wrote in news:FvVMI.30837$ snipped-for-privacy@fx44.iad:

Simultaneously? Zero. Sequentially, in a quick manner... maybe quite a few. Probably get covid from one of them though, depending on the geographic/demographic locale there are hot spots and hot groups with higher incidence. Better use a breather bag and let it do the work.

amdx snipped-for-privacy@knology.net wrote in news:se1a2u$k9e$ snipped-for-privacy@dont-email.me:

West Palm Beach getting nailed right now. One can only pray that Trump is out on a course nearby and God shows us what the word Karma really means.

There is this incorrect mental image of lightning diving into the ground and vanish when a strike hits.

What really happens is that a cloud of charge moving over the ground at some altitude draws along an image charge on the surface below it. When it finds some spot where an arc can form, an impulse of current flows along the surface of the earth to cancel that image charge.

Deep vertical grounding electrodes for lightning protection are pointless, because that's not where the discharge current wants to flow. A grid of wires on, or just under, the surface works much better.

Another point is that a lightning strike is a fairly high frequency event. The inductive impedance of a bend in a lightning conductor may sometimes be enough to cause it to find a shorter path.

Jeroen Belleman

And, keep any induced voltage spikes below a "safe" level.

The question THEN becomes, "what does it take (by way of conductor) to ensure a DURABLE solution?"

For example, if I ran a 1/2 square copper bar AS the conductor (instead of a flimsy "wire")?

Or, relied on a metalic support member (I beam)?

When do you stop worrying about whether or not your protection is still intact (given that you may not actually be on-hand to OBSERVE the actual lightning strikes)?

Thanks, I already have that as a two-volume set.

A deep electrode is preferred because many places don't have good soil conductivity.

And, it is infinitely more PRACTICAL than a "grid of wires".

(We're not talking about a gummit lab that can spend whatever it wants on a solution but, rather, solutions that can be deployed "in the wild" by relatively unskilled professionals. E.g., an electrician likely knows how to install an "earth" for a mains service. Tell him you want a gridded array and he'll look askance at you)

Not necessarily; a grid of wires is a common concrete reinforcement item, available 'free' in a poured slab. Anyone atop such a grid doesn't care much about fields below it into deeper soil.

Cheap solution: tie an overhand knot in each sensitive power and data cord. Leave other appliances connected through straigt-ish wires, as sacrificial defenses. Try to keep the knots separate and not coaxial...

The fact that it is easier to do it wrongly (and unskilled installers usually do it wrongly) doesn't make it right.

Maybe it was diameter, it was very thick. Also, it was steel, not copper.

This one was meant to conduct it and survive.

In a good and robust lighting system low transfer impedance is key. For an antenna system routing the cable in a grounded metal pipe is a durable solution. We used that when doing wind turbines

Refer to NFPA 780. You can find "copies" for download if you look.