[TowerTalk] Grounds, 'remote' towers, 'house' power system

[jimlux]

On 1/13/16 11:03 AM, StellarCAT wrote:
> Please forgive me - I'm not saying its bad practice or one shouldn't do
> it - just trying to understand why.
>
> Lets differentiate between what is always said "you need to connect the
> two together" and WHY you need to do it. Again - if there is a long
> distance except as a DC ground most any kind of connection is going to
> be a poor if not non-connection at RF! So why do it? There will be
> minimal current through it - especially if you've done your job at the
> tower where there is a much lower impedance path to ground. Its not
> going to take the higher impedance path (or of course it will but in
> proportion to the impedances seen) just because its there.
>

The separate bonding wire (leaving aside the size of the wire..) 
provides the "chassis" voltage, so you limit your common mode voltages 
at the shack end.

You don't really care about its RF properties, per se, as long as it's 
close to what your signal and control wires are.  Since inductance 
dominates, basically, if it's the same length, it will have the same L. 
  (the L doesn't change with conductor size very much).

As noted by others, you do NOT want this bonding wire to be an "energy 
dissipation" path.   You'd rather dissipate the energy at the tower (or 
the house, if the strike is at the house).

On  the other hand, if the wire is reasonably sized, you could carry a a 
fair amount of energy without trouble. With all that inductance, the 
current won't be that high.  AWG10 can handle a typical lightning stroke 
without melting.