[time-nuts] thoughts on lightning arrestors

[Bill Hawkins]

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: time-nuts at febo.com
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