Lightning -- to ground or not to ground, that is the qn

[s/v Jedi]

Originally Posted by chicagocpo

Go ahead and protect your metals from galvanic corrosion. The bit of paste will not be an impediment to a 300MV discharge leaping across an air gap measured in miles. At potentials that high current travels down the surface of the conductor and not the interior anyway.

Skin effect is not based on the amount of current. It only occurs for AC currents and becomes more pronounced with higher AC frequency.

I don’t even know that lightning is AC currency, I think it isn’t…

https://en.wikipedia.org/wiki/Skin_effect

[team karst]

Originally Posted by s/v Jedi

..
I don’t even know that lightning is AC currency, I think it isn’t…

https://en.wikipedia.org/wiki/Skin_effect

It has a frequency spectrum still significant at 1MHz. Ever listen to AM broadcast when thunderstorms are within a thousand miles or so?

Also the reason why strapping beats round conductors, unless there are many round conductors in parallel.

[chicagocpo]

Originally Posted by s/v Jedi

Skin effect is not based on the amount of current. It only occurs for AC currents and becomes more pronounced with higher AC frequency.

I don’t even know that lightning is AC currency, I think it isn’t…

https://en.wikipedia.org/wiki/Skin_effect

Let me start by saying that it's been waay too long since I left school and I wasn't even thinking about Mr Maxwell and his equations. I was also incorrect in stating that voltage determines current depth in a conductor. Rather it's apparently the AC components of the static discharge that produce the effect:

"Lightning currents have a very fast rise time, on the order of 40 kA per microsecond. Hence, although lightning is a form of direct current, conductors of such currents exhibit marked skin effect as with an alternating current, causing most of the currents to flow through the outer surface of the conductor.[31]"

Also Wikipedia, but I've already lost the link 🫤

[s/v Jedi]

Yes, I also read up on it and it’s an impuls current with steep edge which creates the RF noise.

Interesting that I remember an insurance survey on the office building I was renting for my business and the lightning rods had round solid copper conductors to ground, maybe 8/16” or 3/8” diameter and not flat plate. And I have seen the same on churches etc.

[GordMay]

Originally Posted by s/v Jedi

... I don’t even know that lightning is AC currency, I think it isn’t…

Lightning is neither AC, nor DC; but a composition of AC, DC, and RF [frequencies 1kHz, to 1GHz.], which is a transient impulse.
It has a changing amplitude, like AC, but a unidirectional flow [polarity: CG or GC] like DC, and the frequency[s] of RF.

[dannc]

Originally Posted by s/v Jedi

...
Interesting that I remember an insurance survey on the office building I was renting for my business and the lightning rods had round solid copper conductors to ground, maybe 8/16” or 3/8” diameter and not flat plate. And I have seen the same on churches etc.

One large commercial building complex I have worked at had rounded lightning rods, I think the were AL but I could only see them from ground level, space pretty close together, with what looked to be AL cable as the ground conductors. 3/8" would be about the size.

We were recently in a museum in the NL that was awesome for many reasons. One reason, was that the museum buildings had two courtyards which had been roofed over to provide more multi storied space. Very nice. What was more interesting to me was that this allowed me to see the roof up close.

I was very interested in the flashing, roof tiles, and the lightning protection system. I could not find photos of the lightning rods, but the ground conductors were of solid metal and braided copper cable. 3/8" would be close to the diameter of both. The solid metal was painted. Both ground conductor types were tied into the roof/wall flashing. This was on the third level in the covered courtyard. I did not think to look to see if they had connected the flashing at the roof level to a conductor on the ground floor. Guess I will have to go back and look.

Later,
Dan

[skenn_ie]

Originally Posted by chicagocpo

Go ahead and protect your metals from galvanic corrosion. The bit of paste will not be an impediment to a 300MV discharge leaping across an air gap measured in miles. At potentials that high current travels down the surface of the conductor and not the interior anyway.

Paste, or even a thin insulator won't affect whether lightning hits the boat or not, but it could affect the route it takes through the boat.

[moseriw]

Originally Posted by GordMay

This standard states, in the first line of its introduction that:
“There are no devices or methods capable of modifying the natural weather phenomena to the extent that they can prevent lightning discharges”.
IEC 62305-1 ➥ https://webstore.iec.ch/preview/info...ed2.0%7Den.pdf

Sorry Gords but this link is like to throw the roman rights enceclopedia to someone who just wants to know if he are allowed to park his car there.

[aberglas]

If those numbers are per year, then in tropical areas, over a 20 year life, maybe 20% of boat will be struck. So quite high actually.

[GordMay]

LIGHTNING TRIVIA:

On April 29, 2020, National Oceanic and Atmospheric Administration recorded [1] the world’s longest lightning flash, at a horizontal distance of 477 miles. It was certified by the World Meteorological Organization (WMO) as the longest lightning strike. The flash stretched from the central coast of Texas, crossed Louisiana, and ended in Southern Mississippi.

The WMO also recorded [2] the greatest duration, for a single lightning flash, at just over 17.1 seconds, on June 18, 2020, a record that still stands today. The flash developed through a thunderstorm over Uruguay and Northern Argentina.

[1] “World's longest lightning flash on record captured by NOAA satellites"
➥ https://www.noaa.gov/stories/worlds-...oaa-satellites

[2] “WMO certifies two megaflash lightning records”
➥ https://public.wmo.int/en/media/pres...htning-records


While the flashes we see, as a result of a lightning strike, travel at the speed of light (670,000,000 mph) an actual lightning strike travels at a comparatively gentle 270,000 mph.

Around the world, there are over 3,000,000 flashes every day. That's around 44 strikes, every second.

Lake Maracaibo, in Venezuela, receives the most lightning strikes on Earth [250 flashes per sq km each year].
Massive thunderstorms occur on 140-160 nights per year, with an average of 28 lightning strikes per minute, lasting up to 10 hours at a time. That's as many as 40,000 lightning strikes in one night.

Until the late 18th century, it was believed that ringing church bells repelled lightning, so many church bells bore the inscription 'fulgura frango', meaning 'I chase lightning'.
During a thunderstorm, bell ringers would run to the bell tower, to ring the bells. However, a high tower with a metal bell was, in fact, about the worst place to be. Between 1753 and 1786, in France, 103 bell-ringers were struck by lightning and killed, resulting in the custom being banned.

[s/v Jedi]

Omg, megaflashes…. as if people aren’t scared enough yet. Soon they will give them names, not just to remember them better, but also as recommended by insurance companies

[GordMay]

These flashes that should remain nameless [#56], AKA: "Megaflashes" are at least 100 kilometers (62 miles) in distance, and do not occur in ordinary thunderstorms.
They need large, electrified thunderstorm clouds, that discharge at low enough rates, to allow for single horizontal flashes, spanning great distances.

These conditions are created by a Mesoscale Convective System (MCS), a collection of thunderstorms, that act as a system. MCSs have overhanging anvils, and rainy stratiform zones, but rarely produce lightning at extreme levels, and such unusual storms have been detected at only a few sites, in the past.

AFIK, no direct connection has been verified, between longer-distance lightning [or longer-duration lightning] and climate change.
But, it’s, perhaps, worth noting that climate models do suggest we can expect more intense storms, with stronger lightning, as Earth’s climate continues to warm. Because lightning is driven by the strength of the convective updrafts, we can expect it to increase, with temperature.

The WMO Archive of Weather and Climate Extremes currently includes two other lightning-related extremes:

One is for the most people killed, by a single direct strike of lightning, when 21 people died, in Zimbabwe, in 1975, as they huddled for safety, in a hut that was hit.

The other is for an indirect strike, when 469 people died, in Dronka, Egypt when lightning struck a set of oil tanks, in 1994, causing burning oil to flood the town.

Roy C. Sullivan, an ex-park ranger [AKA ‘Spark Ranger’], from Virginia, set a record for the most lightning strikes survived - 7.
His first unfortunate encounter, with electrostatic discharge came, in April 1942. And finally, Roy’s chest and stomach were burned, when he was struck during a fishing trip on a boat in June 1977. Thankfully, Roy’s relationship with lightning appeared to end then.
He wasn’t struck again, before he died in 1983, at the age of 71.
More ➥ https://www.guinnessworldrecords.com...n-times-733932

[aberglas]

Thunderstorms are negatively charged at the bottom, positive at the top. So the more common negative lightning is shorter and less powerful than the rare positive lightning.



Not sure if there is anything that can be done with that information though.

[GordMay]

Originally Posted by aberglas

Thunderstorms are negatively charged at the bottom, positive at the top. So the more common negative lightning is shorter and less powerful than the rare positive lightning.

Not sure if there is anything that can be done with that information though.

In a thundercloud, positive particles tend to gather toward the top of the cloud, and the negative ones gather at the bottom. As the charge grows larger, on both sides, an exchange of energy [lightning strike] becomes inevitable.

"Negative lightning", is the transfer of negative charge, from the base of the thundercloud, to the ground. However, not all lightning forms in the negatively charged region, under the thunderstorm base. When a negative charge is transferred from a cloud to the ground, it's known as negative lightning, and it makes up about 90 to 95 percent of all the lightning you ever see. A negative bolt produces about 300 million volts, and 30,000 amps of electricity.

Some lightning originates in the cirrus anvil, or upper parts, near the top of the thunderstorm, where a high positive charge resides. These bolts are known as "positive lightning", because there is a net transfer of positive charge, from the cloud to the ground.
Because an ordinary storm cloud keeps negatively charged particles, between the positively charged particles, and the ground, positive lightning doesn't usually happen, unless there's a strong wind to move the negative charge out of the way, or once most of the storm has cleared.

Positive lightning strikes make up less than 5% of all strikes.
However, despite a significantly lower rate of occurrence, positive lightning is particularly dangerous, for several reasons.
Since it originates in the upper levels of a storm, the amount of air it must burn through to reach the ground usually much greater. Therefore, its electric field typically is much stronger, than a negative strike. Its flash duration is longer, and its peak charge and potential can be ten times greater than a negative strike; as much as 300,000 amperes, and one billion volts.

Positive lightning can strike up to 20 or 30 miles (32 to 48 kilometers) away from their storm clouds. The term “bolt from the blue” references positive lightning, that travels outside a thunderstorm, through clear sky, and strikes the ground, many miles away from its origin.

There is also “bipolar lightning”; lightning that actually changes its polarity; in which both positive and negative charges are lowered to the ground, through the identical lower part of a lightning channel, near the ground. They are usually initiated by upward leaders from tall structures, but they can also be downward flashes. It is no less dangerous than any other type of lightning, but shows that we live on a complex planet, with many aspects we do not fully understand.

The lesson of positive lightning is that [as Yogi Berra said*, about the 1973 pennant race]: "It ain't over, until it's over."
Watch out for the bolt from the blue; and don't relax your lightning safety measures, too soon.


* And, oddly enough: "It Ain't over 'Til It's over": Rethinking the Darwinian Revolution” ~ by Vassiliki Betty Smocovitis
➥ https://www.jstor.org/stable/4331918...n_tab_contents

[Pelagic]

All very interesting but back to basics for a simple sailor:
All Steel Boat-Wooden Masts with heavy Stainless Mast Top Caps and stainless rigging to hull.
What is my weak point in Lightning strikes?