I'll attempt a more non-technical explanation for why you need all your grounds
(Tower, SPG, Shack, Electrical, Arrestors) to be bonded together.
Say that you have all of the above bonded together except for the Electrical
service entrance. We get strike energy induced into our Tower/Antenna system.
Most of the energy will be shunted to ground out at the tower, and then some
more at the SPG (arrestors or just coax shields bonded to the SPG). Some
voltage rise will still occur in the system and will go onto the case of the
equipment inside via the Shack ground.
Now the electrical service ground is not in this group and will/may have a
lower potential (yes it will have some energy induced from the nearby strike
but not the same as the Tower/SPG/Shack system) than the Tower/SPG/Shack system.
Now inside your equipment you have your case at a higher voltage than the
electrical ground (which is connected to your mains box and in turn to your
service entrance ground). Back from Electricity 101, we know that when we have
a voltage difference and there is a conductive path, we will have current flow.
This flow is normally through some component on your equipment's circuitry or
circuit board and voila, zapped equipment.
OK, so now lets bond everything together, outdoors. Now when we ge the induced
energy, everybody (grounds) all rise and fall in that voltage together and
there is no voltage difference inside of your equipment and voila, no current
and no zapped electronics.
Quite simple if you think about it.
Phil - KB9CRY
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