[AReU] Report of the May 2006 meeting.

[Ron Youvan]

Hi all:

   I had an "overhead projector" presentation ready, but the projector was not
available, so I did the best that I could.  I am posting the text from the slides
with a description of the [PIXture].  I do this because it is a very important
subject that will visit us all sooner or later.  We need to keep thinking.

   Ron

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			Lightning, how it works.

			Ron KA4INM Youvan
				- - - -
			To understand lightning
Let's start with a refresher about the  laws of physics that control the way lightning works.
			[PIX:  TRIPLE LIGHTNING STROKE]
				- - - -
Electricity is the flow of electrons in conductors
Everywhere electrons flow, holes flow in the opposite direction, this is because the atoms 
in conductors have insufficient electrons, an excess of holes, sufficient electrons would 
render elements and compounds non conducting.
Lightning is electrons flowing, 	Lightning is electricity.
				- - - -
			It's all about electron flow!
Electron flow is a sub-atomic process.
The outermost electron shell of atoms, the "valance shell" determines whether an 
element is a conductor or an insulator.     A full shell is present in insulators and 
incomplete shells are found on conductors.
				- - - -
				Compounds
Conductive elements can combine with other elements to result in non-conductive compounds.
Example:  Aluminum (an excellent conductor) bonds with oxygen to produce a white clay, 
called "alumina" which when baked at very high temperature becomes a good high Voltage 
insulating ceramic.
				- - - -
The action, electron flow, is the result of pressure
The only pressure exercising a force against electrons creating electron flow is Voltage.
High enough pressure can make good insulators conduct.  Except for a good vacuum!  We call 
this "break down."
				- - - -
			Three kinds of atomic bonds
		create compounds from elements
covalent bonds, ionic bonds and electrostatic bonds.
combinations of these bonds exist in simple compounds such as water.  H2O
		[PIX: "SHARING ELECTRONS OR TRANSFER OF ELECTRONS]
				- - - -
The bonds between the elements effect the conductivity of compounds
Pure (distilled) water is a good insulator, adding a small amount of salt (sodium and 
chlorine) renders water very conductive as do most "contaminants."
Rain and ground water contain enough contaminants to be quite conductive.
				- - - -
				Charges
Like charges repel each other, dissimilar charges attract, with a powerful force.
The differences in electrons (and holes) between the bottoms of charged clouds and the 
surface of the earth create an enormous potential difference, a huge Voltage, enough to 
break down the insulating air making it conductive.  The air molecules become "ionized."
				- - - -
			Lightning begins
with electrons becoming "brushed off" of molecules, droplets of water in clouds by the 
forces of winds and rain.
This (generally) creates a positive change at the top of clouds and a negative charge in 
the lower regions of clouds.
The "charge" on the ground is generally somewhere between these two extremes.
				- - - -
				Lightning
				how it works.

				Ron KA4INM Youvan
					- - - -
Lightning is powerful, Lightning should be feared.
The best defense is to avoid being struck.  The second defense is be prepared for it.  The 
"single point grounding system" is the only way to have your equipment struck and you 
tolerate it.
		[PIX: DIRECT STROKE TO THE GROUND REAL CLOSE]
				- - - -
			How much voltage, how much current?
P L E N T Y!
			[PIX: DOUBLE STROKE WITH BRANCHES]
				- - - -
Holes (or electrons) in the groundwater follow the cloud as the winds blow it across the 
surface of the earth.
When the pressure (Voltage) exceeds the insulation of the air + water (humidity) for the 
distance, a "step leader" of electrons forms and the ground sends up an ionized "corona," 
when they meet we call that  B A L M!  (or Ka-pwie!)
			[PIX: CHARGED CLOUD OVER THE GROUND]
				- - - -
				 POW!
If lightning strikes a conductive object that can tolerate the massive current such as 
this steel tower, no damage (other than an entrance wound) results.
[PIX: TRIPLE STROKE TO TOWER TOP]
				- - - -
If a tower is struck and there is enough mass top have enough "electrons or holes" to 
satisfy the charge there will be negligible ground current, if not even if the tower can 
tolerate the stroke, the "electrons or holes" flowing across and in the ground (water) to 
the tower to satisfy the stroke will cause high potential differences between the various 
ground "rods" as they are passed, creating excessive Voltages between the power ground, 
the telephone ground, the "cable" or HAM radio grounds  and so forth damaging any or all 
electrical appliances, and possibly things that are not electrical appliances like people 
and such.
				- - - -
			Need I say more?
[PIX: ROW OF COWS KILLED VIA BARBED WIRE FENCE]
				- - - -
Florida Man Dies After Struck By Lightning in Head While Talking to Neighbor
Thursday, April 27, 2006

WEST PALM BEACH, Fla. ? A man was fatally struck by a bolt of lightning while talking to 
his neighbor about the upcoming hurricane season.
Harold Bennett, 65, was standing outside his home wearing sandals and no shirt when he was 
hit in the back of his head about 6:30 pm. Wednesday, said his neighbor Judy Thompson.
"It was like somebody had shot him," Thompson, 51, said. "The lightning went right through 
him ... It was horrible."
It was lightly raining when Bennett, a retired gardener, was taking the garbage outside 
and spotted Thompson rearranging furniture.
"He always liked to talk any chance he got, and he asked me if I was moving," Thompson 
said. "I said I was just clearing out the back for hurricane season. He said, 'Now's the 
time to do it,' and started walking toward me. That's when it hit him."
The two were standing about 25 feet away. Thompson was not hurt.
Wednesday's storm brought about 530 cloud-to-ground lightning strikes in Palm Beach County 
between 5 and 6 pm, said Roberto Garcia, forecaster with the National Weather Service
			- - - - - - - -
			What should we do?
   We could: Prepare to be struck.

a. Ground the tower at the shack ONLY using  battery cables.  (from a 1950's Buick battery)

b. Ground everything in the building using the three point grounding plate, nothing at the 
service entrances.
			- - - - - - - -
			What else could we do?	
     We could: Avoid being struck.

a. Don't ground anything.

b. Disconnect all transmission lines except when you are using them.

c. Tie all grounds around the building together to the power ground, don't miss any!
-- 
    Ron  KA4INM