Two of nature's great forces are hurricanes and thunderstorms. A cloud with dimensions measured in miles can accumulate a great deal of static charge during a storm, thousands of times more than any human-built accumulator. When the volts/meter between the cloud and the ground become high enough, lightning bores an ionized hole through the air to some point on the ground. Occasionally the point on the ground is a tall tree. Just up the road from here (MN, USA), lightning struck a tall thick tree during a storm. The tree exploded from the pressure of steam generated by electrical heating during the brief duration of the strike. The trunk was split into four long parts, one of which landed on the roof of the nearest house. That's quite a demonstration of energy. Skin effect did not save the tree.
So I wonder about this concept of a lightning "arrestor". The report referenced by Arthur Dent is quite complete. It also says, at the bottom of page two, "It is impossible to prevent damage from a direct lightning strike ..." Why, then, do people sell lightning arrestors when they wouldn't dream of selling hurricane arrestors? Perhaps it is because we create models of reality from our own experiences. Most of us have controlled electricity in some way, so it ought to be a piece of cake to arrest lightning. People who have witnessed the power of lightning have a different model. This business of grounding or Earthing suffers from differences in scale. Human-generated electricity can be dissipated with ground rods if the soil conditions are right. When lightning pumps hundreds of kiloamps into the ground, the results can be measured in kilovolts per meter. This is what electrocutes cows near struck trees, and why a golfer should hunker down and keep his feet together when his hair rises. You can rely on probability to avoid a direct hit, or you can erect tall grounded masts around your tallest object. This proven method is used by NASA to protect rockets on the launch pads. Each mast provides a cone of protection with an angle of 45 to 60 degrees to the ground. See, for example, http://www.nasa.gov/mission_pages/constellation/ares/lc39b_lightning.htm l - but you may need sand saturated with salt water for it to work. Read the "Antenna System Grounding Requirements" and learn what you can do to arrest the surges that accompany nearby strikes. The term "surge arrestor" is much more accurate than "lightning arrestor". Yours for safe time research, Bill Hawkins -----Original Message----- From: Arthur Dent Sent: Wednesday, November 26, 2014 6:42 PM To: [email protected] Subject: [time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp Here is a link to a good 12 page description of grounding practices/requirements. http://www.reeve.com/Documents/Articles%20Papers/AntennaSystemGroundingR equirements_Reeve.pdf _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
