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Electric Fences
10 June 2007

WeedA WeedB WeedC WeedD

Palms 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.

Tensioner 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..

Problem 1
Problem 2

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