[TowerTalk] Antenna/Tower Grounding (Lightning Protection)

[Jim Brown]

On Fri, 05 Jan 2007 12:13:37 -0500, Les Kalmus wrote:

>Should be OK, no?

Not ideal. The BEST, by far, is for all cables -- power, antennas, 
CATV, telco to enter at the same point so that the ground 
connections between them can be as short as possible. 

Remember that the MOST important element of lightning protection 
is for all of those systems to be at the same potential when a 
strike hits. The wires connecting the grounds will carry current, 
and there will be both induced voltage and IZ drop across their 
inductance. So in the world of lightning protection, SHORT is 
important. 

Gary Schafer, K4FMX, said:

>A single point ground is NOT a place or spot in the earth but it 
>is a point of common connection which can be anywhere designated.

Yes. 

>The whole idea of a single point ground is to have a place to tie
>all lines together with zero impedance between them. You can run
>as many grounds to earth from that point as you desire. But all
>cables entering the shack must be physically mounted to that 
>single point ground panel. 

AND THAT PANEL MUST HAVE A SHORT BOND TO ALL OF THE OTHER GROUND 
BONDS IN YOUR BUILDING -- POWER, CATV, COLD WATER, BUILDING STEEL, 
AND LIGHTING PROTECTION. Caps added for emphasis. This is quite 
important. 

As hams, we tend to focus on our INTENTIONAL antennas, but they 
are only one element of the problem. Lightning will see every 
other conductor in our home as an antenna, and will induce current 
onto each of them based on their length, orientation, and where 
they are connected. The telephone line is a very good receiving 
antenna for lightning. So is the power line. So is the downlead 
from a cable TV system. We ignore them at our peril.

Several of my friends in the pro audio world who have no 
INTENTIONAL radio antennas at all have lost all of the Ethernet 
and printer interfaces in their home office computer systems from 
lightning. 

73,

Jim Brown K9YC