[TowerTalk] Grounding Coax at Tower

[K4SAV]

Having the cables exit the tower above ground is a really bad idea.  
Voltage drop down the tower is very high during a strike.  Anything 
exiting the tower above ground will see a very large voltage impressed 
on the cable at the point it exits the tower.  That translates into very 
high currents on the cable.  Those currents go toward the shack instead 
of into the ground at the tower base.

Other effects:
1. The cable at the point of exit, looses its mutual inductance with the 
tower which increases the currents on the cable.

3.  The cable is now more suceptible to direct strikes.

4.  The cable is also more susceptible to induced currents due to the 
large loop area.

5.  There are no good points.

Jerry, K4SAV

jimjarvis at optonline.net wrote:

>TT:The concept of having the coax and other lines leave the tower ABOVE earth level, is alien to me.   I've always felt that the capacitance of the coax bundle to earth would tend to limit a strike's current in the direction of the shack, in favor of the lower impedance tower connection.HOWEVER,  you COULD have the coax leave the tower at 10' or so,  making a solid connection to the tower at that level, and letting the tower be the conductor to the earth ground system.   The problem with flying the cable bundle, however, would seem to be twofold.   1)  reduced capacitance to earth, due to increased distance, and therefore reduced strike current along the bundle;  and 2) having the flown cables act as a larger loop, in the event of a nearby strike.   In the latter case, there would be greater current induced in the secondary turn of the 1 turn transformer represented by the tower-cable system.  Does anyone see a flaw in that thinking?N2EA
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