[Elecraft] OT- Tower grounding

[Jim Brown]

On 5/9/2013 11:57 AM, Don Wilhelm wrote:
> Option 2 only.
> In fact, if you want to make it even better, run a #6 copper wire all 
> around the perimeter of the house with a driven ground rod anywhere it 
> makes a turn more than 30 degrees.  That perimeter wire provides a 
> path for lightning instead of allowing it to punch a hole in your 
> building foundation.
>
> I would also suggest at least 3 radial wires from the tower (length at 
> least 1/2 the tower height) with driven ground rods spaced twice the 
> length of the ground rod.

I like this advice, BUT -- also make sure that ALL other grounds are 
also bonded to this ground. That includes the common connection of all 
the gear in your shack (which should have a bond from one chassis to 
another for each piece of gear), the antenna entry point, cable TV 
system, telephone system, cold water (it it's metallic), structural 
steel if there is any, and the green wires for all the outlets in your 
shack.

A quibble though -- the "green wires" for all the outlets must be bonded 
to the enclosure of the main breaker panel, and they MUST be connected 
to your gear via the power cord. That combination of wires IS a 
connection through the house, although it's not a very good one, both 
because the conductors are small and they're long, so they're inductive. 
SO -- my advice, and what I've done in MY shack (where power is on one 
side of the building and the shack is on the other), is to do BOTH the 
perimeter wire (#4) with rods at multiple points along the run, and 
bonding the steel conduit (EMT) that carries wiring for the shack to the 
operating desk common point, and to the coax entry point.

The fundamental concept is that you want to provide a robust, short path 
to earth for the strike (which can come in on your antennas, the tower, 
a phone line, a CATV cable, the power line, and even the wiring inside 
your home), and for everything in your premises to stay as close to the 
same potential as possible. To accomplish that, you want multiple paths 
to earth (ideally close to every entry point), and the lowest possible 
IMPEDANCE between everything in the premises, with conductors large 
enough that they can carry as much current as practical before they 
melt. :)  Because lightning is an RF event, with a very broad energy 
peak around 1 MHz, the impedance is mainly INDUCTANCE, not resistance, 
which is why "short" matters, and why more parallel inductors are better 
than one.

73, Jim K9YC