Mike Kaliski wrote:
"Rick (W-A-one-R-K-T)" wrote in message
news
In the 2007 ARRL Handbook page 3.6, there is a discussion of building a
ground ring around the base of the tower, connected to three ground rods
each connected to each leg of the tower.

In the narrative it says "Space rods at least 6 feet apart" but then in
the caption for the accompanying drawing it says Locate ground rods on the
ring as close as possible to their respective tower legs".

On a Rohn 25G, the rods can't be "as close as possible" to their
respective tower legs and still be anywhere near 6 feet apart.

So, which is it ... close to their respective tower legs, or 6 feet apart?

What is the reason for the 6-foot separation, anyway? The rods all go
into the ground. Why would it make a difference if they're closer
together than 6 feet?


Rick

General guidance is to space the rods a minimum of their length from each
other. So 8 foot rods should be at least 8 feet apart for optimum results.
Its all to do with voltage gradients through the ground when a fault current
is flowing through the electrode. Wider spacing tends to reduce the
steepness of the voltage gradient and is considered to reduce the risks to
people or animals in the vicinity of the earth electrode in event of a fault
or lightning strike. Ground voltage gradients of only 50 volts can be lethal
to cattle or other quadrupeds.

Also to reduce the grounding resistance. Close rods don't reduce the
resistance as much as farther rods. This is probably a more common
reason for multiple rods, rather than reducing step potential. Places
with step potential hazards (e.g. electrical substations) tend to use
ground grids, since, as long as you're buying all that heavy copper
cable to connect the rods (not to mention the above ground
infrastructure), you might as well just bury it.