wrote in message
oups.com...
I am trying to gain a better understanding of the issues associated
with lightning and grounding, particularly for an amateur radio
station. I would greatly appreciate any answers to my questions, given
below.

1.) It seems like lightning "finds" a path before actually discharging
through it. Is this correct? How fast is the process of finding the
path?

no, it takes all the possible 'paths' at once. ones that end in high
impedances reflect most of the current back and then it goes down some other
path... ones that end in low impedances suck more current out of the system.


2.) Does lightning discharge over one path or many paths? In other
words, if lightning strikes a point, and there are two paths from that
point to ground, is the energy shared - like a current divider? One
would think that this is what happens, with the sharing based upon
relative impedances to ground.

yes, as above... it goes down all paths and ends up sharing them based on
relative impedance exactly like a current divider but with time delays based
on the lengths of the paths and terminating impedance.


3.) This talk about "single point ground" can be confusing, especially
when the solution involves multiple ground rods. I believe we are
really saying that the station (equipment) should be connected to
ground at only one point - but you can have any number of ground
connections (i.e., like ground rods) otherwise.

yeah, thats a reasonable way to look at it. it kind of looks like an
hourglass with everything being connected at one common point and spreading
out in the shack on one side and into the ground on the other side but
possibly with multiple connections on both sides.


4.) Does the size of an antenna affect the probability of its being
struck by lightning, all else being equal? What is the governing
relationship?

the bigger it is the more likely it is to get hit.


5.) Finally, consider an amateur antenna on a pole, located some
distance from the service entrance of the house. Let's say there is a
copper cold water pipe right at the service entrance. Is it wise to
place a lightning rod (or rods) right under the antenna, place an
arrestor on the coax there and then another arrestor where the coax
enters at the service entrance? Is a ground wire needed between the
remote ground rod and the cold water pipe?

this is actually a couple (relatively) unrelated questions.

the more rods the merrier. the more paths you can give lightning the less
of it will get into your shack. just don't put the rods too close together
or you are wasting money, put them at least their own length apart from each
other and connect by heavy wire, cadwelded, etc, etc.

yes, you can put arresters at each end of a cable, but its probably only
worth it if the cable is relatively long... on a swag i would say if its
shorter than 100' its probably not worth two arresters, just put one at the
service entrance. the function of an 'arrester' is to just equalize the
voltage between the shield and center conductor and since the critical point
for that difference is at the radio end that one is more important.

i believe code requires water pipes to be connected to the service entrance
ground. the service entrance ground should also be connected to the ground
at the antenna, so indirectly the water pipe and remote rod would be
connected.


Thanks in advance,

-JJ