Lightning, Grounding, and Bonding

ęCopyright 2002, LLoyd W. Phillips

Introduction:

Compare lightning to a giant Peltier Device in reverse.  You put atmospheric differentials in, and get lightning out. 

Deserts, volcanoes, diesel engines, etc., add particulate matter (dust) to the atmosphere.   The dust, moisture, and differential atmospheric pressures (isobars) and temperatures cause electrical charges to form  by "stirring" this atmospheric "soup."  This is the "junction."  The sun supplies heat and (the thinning ozone layer) causes even greater ionization and atmospheric turbulence, resulting in more heat in one mass (earth or another cloud), while colder air fronts and frigid high altitude temperatures supply the cold side. Cloud masses are basically water in various states with particulate matter. There must be a collision of atmospheric fronts, with moderate to high temperature differences, for lightning to occur.

Cloud to cloud and intra-cloud lightning attempts to "equalize" upper atmosphere potentials, while earth-sky lightning attempts to equalize potentials between the earth and upper atmospheric masses.

Note: As of May 3, 2002, the National Weather Service has no way of monitoring particulate mater, and checking with Stephen Lord at the Environmental Modeling Center, no weather prediction models factor in the heat contained by matter in atmospheric suspension. 

 RADIO FREQUENCY (RF) RADIATION CAUSED BY PUBLIC UTILITIES 

An important consideration in the search for Radio Frequency sources that block communications and make garbage out of Broadcast, Short Wave, DTV and HDTV, and signals well into the microwave bands, is the RF induced on power lines by faulty connections, insulators,  LAs (lightning arrestors (surge protectors)), etc.  The transmission lines and vertical grounds then act like a giant WINDOM antenna, capable of radiating many frequencies, some with many times more Effective Radiated Power (ERP)  than a tuned dipole or 1/4 wave vertical antenna.

DEFINITIONS / FAQs:

Lightning is an electrical discharge through the atmosphere, which attempts to bring (oppositely) charged masses back into electrical equilibrium.

Lightning Channel is the path that lightning takes through the atmosphere between charged masses.  There can be many branches, but usually only one lightning channel.  Lightning travels in 30-50 meter increments, called "step leaders." 

Voltage in a lightning channel can exceed 1,000,000 volts

Current in a lightning channel can exceed 200,000 Amps ( 200 kA ), with slew rates in excess of 400,000 Amps per microsecond.  A typical 30 foot vertical #6 copper wire "ground" on a utility pole has a relatively high impedance at this frequency, and serves more as a "pointer," rather than a road, much like a painted line on a highway.   Because lightning has a "slew" component (change in electrical properties over time [ kA/microsecond ]), it has Alternating Current ( AC ) characteristics, and AC laws can be applied. 

Temperature in a lightning channel can reach 50,000 degrees Fahrenheit. 

Skin Effect is the delay at the inside of a conductor compared to the outside surface of the same conductor as frequency increases. With lightning, the existing magnetic field tends to push a newly applied charge to the outside.  A 4 inch wide, flat, bare copper ribbon only 0.030 inches thick provides a better path to ground for lightning than a solid 4 aught copper conductor with insulation. It's the outside surface area that counts, not the inner circular mils. Painting a copper ground strap reduces it's efficiency.

SUMMARY:

Rather than bore you with long-winded technical jargon, charts, and details, lets go right to the summary. 

IMPORTANT CONSIDERATIONS FOR EQUIPMENT and JACKETED HELIAX RUNS:

If you have a 2000' tower, and run a 2000' Heliax line to your antenna, with the Heliax insulated from the tower, you can usually expect lightning damage to equipment at both ends. 

Lightning hitting the leg of a tower is dissipated to other legs through cross-members, and the legs act as inductors, while the cross-members and braces have both capacitive and and inductive characteristics. This changes the velocity of the path. The insulated, jacked Heliax has a straight shot down the tower, and to your equipment.

You need to keep the power in both paths at an equal speed and potential by bonding the outer conductor of the Heliax to the leg of the tower every fifty feet or so.  In communications equipment rooms inside buildings, mount your equipment on isolation pads that extend about 1 foot beyond the base of the floor mounted equipment cabinets. Suspend all power, RF, and Telco lines in overhead troughs. Run heavy copper flashing grounds in all troughs.  When lightning hits, your equipment should be at or near the same potential as all incoming lines.  DO NOT GROUND THE EQUIPMENT CABINETS SEPARATELY to any other ground, except the overhead trough ground..  Your goal is to keep them isolated from the floor and other ground paths.

LINKS:

NOOA.GOV 

LIGHTNING & Utility Companies 

 

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