[TowerTalk] Antenna/Tower Grounding (Lightning Protection)

[Telegrapher9 at aol.com]

Gene,

does anyone run simulations or calculations on lightning strikes. A common 
direct stike is 100 kA with a risetime of 8 us, correct? If so, using an 
inductance of 200 nH/ft, the voltage drop along 1 foot of wire is 2.5 kV. And we can 
calculate the low frequency impedance of a ground system. Let's say it is 1 
ohm. Now we have 100 kV between the tower base and earth ground. 

Using some ball park numbers like this we should be able to determine the 
currents and potentials at various points in the system. Then appropriate series 
Z and shunt Z can be applied to design for survival of equipment. 

I'm thinking of doing it via design rather than blindly by code. I suppose 
that there is nearly 100 years of experience contained in the codes that will 
lead one to success. But perhaps a good understanding of the nuances can help 
one to gain several dB of margin by some simple additions. 

Can someone steer me to some numbers on lightning? Thanks. 

    Dave WX7G