Some other considerations:
The size of most ground rods in the U.S. are based upon the efficient
grounding of 60 Hz AC from the power company. Anything larger in
diameter than around 5/8 of an inch does not increase the grounding
effect, thus the selection of that size by the U.S. NEC (National
Electric Code).
Since fencers (energizers) have very short pulses in the microsecond
range (millionths of a second), they can benefit from improved grounding
with the use of multiple grounding rods spaced at least their length apart.
This is also very important with lightning protection. I suspect that
many farmers do not properly protect their systems from lightning
strikes, but the typical spark gap type lightning "arrestor" plus an
added choke coil in series with the main feed from the high tensile
terminal may not protect against direct strikes. (Yes, we have had
direct strikes that sever the wire 100's of yards from the fencer and
having the fencer totally destroyed.)
Ideally, the lightning ground should be better than the earth ground at
the energizer so that it shunts the spike to ground well before it
reaches the unit but I suspect this is rarely done. In rocky ground, the
use of bare copper wires that are spread out around a shorter rod,
(shorter, because you can't get it in the ground very far), can work to
your advantage even if not buried very deeply. Scientific measurement
has shown that due to the law of diminishing returns the length of the
wires should be under 50 feet long. I would recommend more wires at less
than half that distance as a better choice if you have difficult soils
that would need this kind of grounding. Thus, leon's recommendation of
having the ground rods in a group is better than having them in line
over a long distance. And also keeping the fencing grounds away from the
AC service ground.
I strongly recommend the use of MOV spike protection if using an AC
power source since it is very common to have power surges on AC power
lines from both storms and from switching transients, inductive loads,
etc. These devices typically cost less than US $10 although some are
better than others depending on the number of MOV's and how they bridge
across the AC hot/neutral/and ground.
The conductivity of copper is about 4 times that of zinc. I generally
recommendation the use of copper wiring and copper clad steel ground
rods with bronze clamps since the conductivity is improved over the zinc
used in galvanized rods and wire. If this is not available locally, then
using the galvanized product is still acceptable. As long as you do not
have any dissimilar metals from the fencer to the ground system, you
should not have difficulties. The only connection points that would be
dissimilar would be at the fencer ground terminal and at the ground rod
clamp. The U.S. fencers often have brass screw terminals which should
not pose a problem with the use of galvanized materials although the
copper would be better. Same thing with bronze clamps on the ground rods.
The grounding effect of multiple shorter ground rods versus a fewer
number of longer ground rods, is dependent upon local conditions and
soil structure.
Sincerely,
Rick Williams
Misty Ridge Farm
Viroqua, WI
leon wrote:
>Proper galvanised stakes (Gallagher dealers should be able to supply them)
>are important.
>
>Copper �rods� are likely to be too thin if less than an inch diameter and so
>will have little bearing surface (contact) with the soil and will not be
>able to be driven in two metres deep. Also copper will corrode galvanise
>wire where they join. Copper should not be used anywhere in electric
>fencing, but if copper or copper coated pipes are used, use copper wire from
>the energiser and copper clamps.
>
>If you can�t buy proper earth stakes that are about two inches wide, then
>get galvanised pipe of at least 1 inch diameter (preferably larger) and at
>least two m (6 ft) long. Trials showed that two three metre long (deep) ones
>gave better earthing than three two metre long ones. Depth is important,
>especially in dry soils.
>
>At least three two metre deep stakes are necessary, but if the energiser is
>around 20 joules then at least five will be necessary and to reduce the
>lightning risk, in a square formation with one in the middle all at least
>three metres apart. If a lightning diverter is incorporated in the system,
>five in this shape will protect the energiser better than a smaller earth
>system or one where five stakes are in a line fifteen metres long.
>
>Rust and corrosion occur more near the surface so use coated cable rather
>that bare wire. All can then be at ground level.
>
>In very dry areas a bentonite system may be necessary.
>
>If milking, place the earth system well to one side of the parlor to prevent
>shocks going through the parlor and position it well away from the mains
>earth peg which might be only a metre deep and not made to conduct more than
>a trickle of current.
>
>
>
