Lightening

Atmospheric static discharges, commonly known as lightening, are perhaps the most costly natural phenomenon to us as ham operators.  Sure, wind and ice tally up quite large numbers of antennas and towers, but lightning has the ability to get the tower and antenna, a rig or two, as well as other valued possessions.  I personally know a ham that lost a new rig, the antenna to which it was connected, two garage door openers, every TV and stereo in the house, the microwave, the dishwasher and several breakers in the panel box.  Fortunately nobody was injured in this strike. 

This strike came in on a 10 meter vertical antenna that was attached to a Kenwood TS940.  This damage could have been prevented.  Before I list some tips for keeping lightning at bay, I have some interesting facts for you.

1.	According to the National Geographic Society, Lightning strikes somewhere on the surface of the earth about 100 times every second.
2.	The National Lightning Safety Institute says that in the decade from 1040 to 1949 that lightning was the single most deadly natural disaster averaging 337 fatalities a year.  That’s more that twice that of tornados in that same time frame.  It still accounts for an average of 73 deaths a year and is still almost twice that of other natural disasters.
3.	A lightning bolt reach voltages of more that 1,000,000,000, (1 Billion) volts.  It may also have a charge of more than 10,000 amps.
4.	Can generate temperatures as high as 90,000 degrees Fahrenheit.
5.	5 % of those killed by lightning were playing golf and 2.5 % were on the telephone.
6.	73% of the people killed in the United States were killed in June, July and August. Last year the top five states for lightning fatalities were Florida, Michigan, Texas, New York and Tennessee.
7.	Santa Clause named two of his reindeer after this phenomenon, Donner (Thunder) and Blitzen (Lightning)
8.	Lightning can and does strike the same place twice.

When it comes to lightning protection, three words come to mind, grounding, grounding and grounding.  The question on many lips here is usually “how?”  First thing to bear in mind here is that am improperly installed lightning protection system is worse than none at all.  There are many trains of thought on protection systems but the one to which I subscribe is preventing the strike from occurring instead of trying to harness the beast after the fact.  To that end we will march on.

We all know that lightning is created by differential static charges in the atmosphere.  These charges can be cloud to earth or cloud to cloud.  The cloud to earth static is the one we as hams worry about.  I use the word earth so as not to be confused with the term ground as in electrical ground.  For our British friends that may be reading this, kindly reverse the two terms.  

A lightning protection system provides a designated path for the dissipation of static charges. The system neither attracts nor repels a lightning strike, but simply intercepts and guides the current harmlessly to ground. A lightning protection system is made up of several components.

a.	The lightning rod, sometimes called the air terminal.  You want this to be the tallest item around.
b.	The ground rods, sometimes called the ground terminal.  You want these to be at least 10 feet long, ½ inch or more in diameter and inserted into the ground with no more than 3 inches above ground.
c.	The conductor.  This is a copper wire of substantial current carrying capability, #4 AWG or larger.

If you look above to the statistics, you’ll see that a single strike can deliver a billion volts at 10,000 amps and create heat sometimes to 90,000 degrees.   Bearing this in mind, we know that it will be easier to prevent a strike than to control it.  Those numbers alone tell us that the protection system could not contain the energy of a direct hit.  I say all this to prove that your protection system will dissipate the static charge before it build to those numbers.  In other words, the lightning rod DOES NOT attract lightning.

Here are some quick tips for building your tower protection system.  The first tip is to use good bonding techniques to affix your conductors to your terminals.  Copper welding kits are the best for this and are available at most electrical supply outlets.  While you are there, ask them how to use these kits.  They will be more than happy to help.

Second, be ware of oxidation and corrosion caused by dissimilar metals.  Aluminum does not play well with others.  If you must mate copper to aluminum, use a device known as a bimetal split-bolt.  This handy item has special plating that does work well with both copper and aluminum.  It has bar in the center separating the cavity into two compartments.  DO NOT put the copper and aluminum in the same compartment.  These too, are available your local electrical supply outlet.  

Third, when it comes to ground rods, the bigger, the better.  If you can find some 20 feet long and ¾ inch in diameter, buy them.  A good system should have 3 rods.  Run your conductor from the second rod to the first and from the second to the third.  This makes a tee and not a loop.  By all means, if your connections are to be under ground, WELD them.  Mechanical connections can and do fail.  If this connection is under ground, you will never know until……

I hope this helps some.  If you have questions, suggestions, or a topic you think I should cover, email me at wy7fd@arrl.net