"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.

Placing electrodes close in to tower legs will reduce the path for current
to flow if the Rohn 25G tower is struck by lightning and represents a
compromise between optimum earthing practice and discharging excess voltage
on the tower by the most direct path possible. Precautions are normally
taken to keep people and animals away from the immediate vicinity of the
base of an antenna tower, so this method of earthing would tend to reduce
the hazards associated with this particular design of antenna tower. The
requirements for other types of antenna tower installation can be very
different depending on the width of the base of the tower, number of support
legs and method of anchoring into the ground.

Mike G0ULI