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

[Roger (K8RI) on TT]

At 75 feet from the entrance, my tower is close enough that it's all one 
big ground system. I used to put arrestors at the tower base and house 
entrance. I had to replace those at the tower often, but not the house.  
Then I asked, Why? They both do the same thing (protect the equipment in 
the station), but with a much higher voltage at the tower.  The series 
of pulses sees the coax as a big inductor and capacitor, automatically 
reducing the voltage between the center conductor and shield. What 
useful purpose do the extra arrestors at the base of the tower serve?  
They certainly do not protect the coax as the voltage across the 
conductors is highest at the top of the tower with a reduction by the 
time it reaches the bottom.  If it held up to that, the coax from the 
tower to the house will see even less and fail less while still 
protecting the equipment. The same for the rotator and control box.

I took out the arrestors at the base of the tower, but I rarely have to 
replace ones at the house entrance/SPG.  The cables run underground from 
the tower to the house. There is inductance in those lines, but also a 
large capacitance to ground.  The capacitance is essentially a series of 
parallel capacitors to ground so the voltage is lowered as you move 
toward the house end.  The coax jacket is grounded to the tower, top and 
bottom. At some point the distance from the tower to the house becomes 
great enough that they can be treated as separate entities.  I believe 
Polyphaser says >= 200 feet you no longer need to maintain a continuous 
ground.  I believe it said, needed, not that they must be seperate, but 
if not needed, why go to the additional work and expense of doing it? 
None that I can think of

It's only a single installation, but it appears to work for me.


73

Roger  (K8RI)


On 1/13/2016 Wednesday 1:30 PM, Gary Schafer wrote:
> Lightning can be thought of as a constant current source. A strike will
> contain X amount of amps and it will conduct that amount of current to
> earth. If there is resistance/inductance in the path, the voltage will rise
> to whatever is needed to maintain the X amount of current.
>
> So yes, leaving ungrounded coax cables laying on the floor is a bad idea.
> The voltage will rise until it is high enough to create an arc to a path to
> earth to dissipate the charge.
>
> You most always should have two ground systems unless your tower is right at
> the shack entrance.
> The tower should have its ground system at the tower base, ground rods
> radials etc.
> Then you need a similar ground system at the shack entrance where your
> single point shack ground system gets grounded. This needs ground rods,
> radials etc.
>
> You should always tie both ground systems together and to the power ground
> for safety. The ground lead between tower and shack will dissipate some of
> the lightning energy and help equalize voltages in the area but it should
> not be a substitute for a ground system at either end.
>
> Both ground systems are important as you want to discharge as much energy to
> earth right at the tower as possible if the tower is struck or energy is
> induced into it.
>
> The ground system at the shack will take up a lot of what is left over that
> the tower ground system did not take care of and it will dissipate a large
> part of energy if a strike comes in on the power line or phone/TV etc.
> lines.
>
> Having all the equipment, power, coax etc tied together at the single point
> ground panel keeps the potential the same on all lines as they enter the
> shack. The fact that the single point panel has a ground lead a few feet
> long to its ground system will allow some voltage rise there but all lines
> to the equipment will have near equal voltage.
>
> If the power comes into the shack from a ways away of the other side of the
> house a good thing to do is run an ac line (from an outlet in the shack)
> over to the single point ground panel where AC protectors are placed on that
> line and then power all of your equipment only from that AC outlet on the
> single point ground panel. That will place the AC power at the same level as
> the coax lines.
>
> 73
> Gary K4FMX
<snip>

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