[TowerTalk] What is a single point ground (again)

[Gary Schafer]

I posted this about a month and a half ago. I see that it is again needed.
:>)

Many are confused by the SPG term as they try to envision it as how they
would  tie their ground system together.

The "single point ground" (SPG) really refers to the bonding of the
equipment that you are trying to protect and all of the cables feeding that
equipment. 
It has nothing to do with the rest of the ground system other than being
bonded to it.

The ground system can and often is made up of many different individual
grounds consisting of ground rods, radials, tower ground  etc.

The SPG should be referred to as a single panel where all cables that enter
the building pass thru and are bonded to that panel either  directly or thru
lightning protection devices.
That panel is then connected to the station ground system by a heavy, low
inductance conductor as short as practical.

The ground system directly connecting to the SPG panel should be made up of
radials and ground rods starting as close as practical to the SPG panel.
Other ground systems, such as utility ground, tower ground etc should be
bonded to the SPG panel in as direct a route as practical.

If the utility power is more than a few feet away from the SPG panel, the
most practical way to maintain a single point ground system is to  run a
power line over to the SPG panel and put a protection device for that power
line directly on the SPG panel, bonded to the SPG panel, and then power the
equipment only from that power line, after it has gone thru the SPG
protector. 
By doing this you do not have multiple paths for current flow into the
equipment, everything is maintained at the same common potential and it is
all held close to ground.

Think of the SPG panel as a window made of a sheet of copper or aluminum. In
order for anything to enter or leave the room it must first pass thru that
copper panel.

The whole idea of a single point ground system is to not  allow any
lightning energy to flow thru any piece of equipment and secondly to hold it
all as close to (earth) ground as possible.

73
Gary  K4FMX