Electric Fences
10 June 2007
The saga of the trespassing coffee cows continues. If you haven't read
part 1 and part 2
yet, you should probably do that first. That will explain why I've been
spending so much time with the electric fence recently. I'm hoping that
the electric fence will help keep the cattle away from my Kona coffee.
There are three types of fencing surrounding various parts of our
coffee farm. The section along the cattle ranch is ten zillion
year old barbed wire fencing. It has all but rusted into oblivion
and is now nothing but a hazard to wayward animals and careless coffee
farmers.
The best section of fencing is along the lower boundary of our back
field. It is three feet of woven wire (a 6' tall roll cut in
half) on the bottom half of the fence with a couple strands of electric
fencing along the top. I wish I had this fencing around our
entire place. I might add a stand-off electric line about a foot
up from the bottom. The electric lines on the top keep animals
from jumping over and the stand-off line keeps animals from rubbing
against, pushing on or digging under the fence. This fence is
tremendously effective, acting as a visual,
physical and psychological barrier. Unfortunately only one small
section of the farm has this good fencing. I did the math and replacing
the existing fencing around our macadamia orchard with this good fencing would
cost a couple thousand dollars, not including labor. I don't think that
will be happening any time soon.
Most of our farm is surrounded by five strands of electrified high-tension
wire. Electric fences are nothing but a psychological barrier.
When an animal first encounters the fence it is naturally cautious, probably
sniffing or nibbling the fence to see what it is. If nothing is touching
the fence it just sits there quietly, with no way to tell if it's charged or
not. Touch it and WHAM, it delivers one heck of a shock. It pulses
once per second with 8000 volts. I can tell you first hand that the
tingling lasts for several minutes. The current is very low so there is
no permanent damage. It's only lasting effect is psychological.
Touch it once and even the dumbest of animals will learn to avoid it. Of
course Kona coffee farmers are exempt from this learning.
The most difficult part of an electric fence is keeping it from
shorting out. If you're planning to install an electric fence, the
first piece of advice I'd offer is "Don't plant palm trees next to
it." I'm always dragging our neighbor's palm fronds off our
electric fence. Usually I can just lift the frond off the fence
and it's fine but every once in awhile *ZAP* the fence will get me
through the frond, followed by several minutes of swearing. The
fence is configured in sections so if there's an on/off switch nearby,
I'll turn that section off first. More often than not though,
after a few moments of staring at the innocent looking fence, I'll decide
that the walk to the closest switch is too far and figure I can lift the
frond off between pulses. I'm successful with this just often enough
to keep me thinking it works.
Besides palm fronds there are a million other things that can short
out and break electric fencing. Luckily, repairing the broken wire
strands is fairly straightforward. Step one is to turn the fence
off, there's no fix-it-between-pulses this time. It's best to turn
the entire fence off, turning off just the section you're working on is a
good way to forget and accidentally move on to the next section. Even
really smart people can make that mistake.
Once the fence is off, it's safe to begin repairs. They sell special
connector bolts but I've found it easier to simply tie the two strands of
wire together. I might seem easiest to twist loops into the
end of each strand. Unfortnately this doesn't work well because
that single point of contact creates a poor electrical connection and
the wires tend to snap at the loop tips. Only amateur farmers use
loop knots like this. Of course this coffee farmer has
never used such a knot. I don't know where loop knot came
from. It must have been tied by evil elves.
The fence manual recommends using a reef knot. That creates more
electrical connections without creating any pinch points. Getting
a reef knot tight is difficult with the stiff, brittle wire so I've
invented my own "knot" that I think works even better. I pull the
two strands tight and hold them in place with a pair of vice
grips. Then I wrap the end of each strand around the trunk of the
other strand. In my opinion this creates the best electrical
connection, has no weak pinch points and is easy to tie by hand.
After tying all the broken strands back together, the next step is to
tension the fence. This is accomplished with special tensioner
wheels. The wire is rolled tight around the tensioner then held
in place with a clip. It's easy to do as long as I remember to
bring my wrench handle along, otherwise it's a pain in the rear and
next to impossible to get the fence tight.
Anything touching the fence will cause it to short to ground, rendering
it ineffective. Weeds are the primary culprit. Living in
the tropics, weeds can grow with amazing speed and vigor. All
weeds must constantly be removed from around the fence. It takes
a little practice to use the weed whacker without tangling it in the
electric fence wires. With several thousand feet of fence around
the farm, there's plenty of opportunity to get good with the weed
whacker.
When the fence is repaired and all the weeds are cleared then it's time
to turn the fence back on and check for shorts. If the voltage
isn't high enough that means the fence is shorting to ground
somewhere. Sometimes the short is obvious, other times it take a
bit more investigation. Turning the fence on and off in sections
can help isolate the problem area but the best indicator is usually the
snapping sound of the spark with every pulse. The snapping sound
gets me close then I have to visually inspect the fence until I spot
the problem. Here are a couple pictures, can you tell what is
wrong with the electric fence in these pictures? Don't click on the
picture to see the answer until you think you see the problem..
Answer 1: The little plastic pin in the top bracket has broken,
allowing the wire to fall out of the bracket and contact the steel fence post.
It's easy to see in this picture, not so easy to spot from a distance while
walking along the fence line. This was a solid connection so there was
no snapping spark sound.
Answer 2: Since the steel pole touches the ground, the electric
wires can't touch the steel pole or the entire fence will short out.
That's what all the white insulators are for, they isolate the fence from the
pole. The two sections of fence still need to be electrically
connected. The wire that does this used to have a small piece of plastic
shoved between it and the steel pole. When that plastic fell out, the
fence shorted out against the pole. The proper solution would be to use
a heavy gauge insulated wire to jump the two fence sections together.
The Kona coffee farmer solution was to use an old piece of hose as an insulator.
Problem 1
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Problem 2
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