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About the Author
Ann Larkin Hansen is the author of The Backyard Homestead Seasonal Planner, The Organic Farming Manual, The Electric Fencing Handbook, Finding Good Farmland, and Making Hay; coauthor of A Landowner’s Guide to Managing Your Woods with consulting forester Dennis Waterman and master logger Mike Severson; and coauthor with her husband, Steve, of Maintaining Small-Farm Equipment. She has been a journalist for more than 30 years, specializing in organic agriculture and sustainable forestry. A homesteader and a small-scale organic farmer, she lives with her family on a farm in northern Wisconsin.
Read an Excerpt
HOW AN ELECTRIC FENCE WORKS
When an animal touches a charged fence, the electricity passes through its body to the ground and back to the energizer's grounding system. This completes the electrical circuit and gives the animal a memorable shock. The shock is what makes the fence work: animals conclude that the pain isn't worth the reward of pushing through the fence. This is how they are trained.
The intermittent static electrical charges on an electric fence are generated by a fence energizer (also called a fencer, power unit, controller, or charger), a box of electronic components that convert standard lowvoltage current from an electrical outlet or storage battery to the high-voltage pulses along the fence wire.
Elements of Electric Fencing
The most important principle of electric fencing is that electricity doesn't shock unless it is moving. For electricity to move there must be a complete circuit; that is, the charge generated by the energizer must be able to find its way back to the energizer.
Clearly, then, the energizer is only part of the circuit; contrary to popular belief, it alone does not control the effectiveness of an electric fence. The type and condition of the wires and whether there is enough moisture in the ground to conduct electricity both play critical roles in how effective a fence will be.
Two additional factors help to make a fence effective:
* Properly insulating the charged wires from the ground so the current flows only through the animal
* Having a good ground system, so that when the current is flowing it doesn't get diluted on its way back to the energizer
To understand any discussion of electric fencing, it's helpful to know some basic electrical concepts. The simplest way to grasp these is to compare the current along a wire to water in a hose.
Volts are the equivalent of water pressure. The more pressure (volts), the farther the charge can jump. Voltage must be higher if the charge has to jump farther to penetrate thick fur or hair.
Amps are the equivalent of water volume. The longer your fence or the more faults present, the more amps you'll need to fill the line.
Watts are volts x amps, and are used to describe how much electricity is being drawn from the power source. Watts also underlie the next, very important concept.
Joules are watts multiplied by time. One watt for one second = one joule. The "size" of a fence energizer is commonly ranked by the number of joules it generates. Joules are related to the amount of fence the energizer is capable of charging effectively, but the relationship is not straightforward, as we will discuss in chapter 2.
Because you want the circuit to be completed only when an animal touches the fence, the rest of the time the wire must be insulated from the ground. This separation is accomplished by using nonconductive materials (stuff that won't conduct an electrical charge) to isolate the wire from contact with any conductive materials touching the soil.
Posts are what hold the wire off the ground. If they are made of conductive materials (such as metal T-posts), you must attach insulators between the post and the wire.
If the posts are made of nonconductive material, such as fiberglass or plastic, you can attach the wire directly to the post. You can even use metal clips to hold the wire on a fiberglass post. The clip will then be charged along with the wire, but the charge cannot get to the ground through the fiberglass, and that's all that matters.
The Grounding System
To complete the electric circuit, you must bring the electricity flow home to the energizer. You do this by creating an antenna in the soil to attract and gather the electricity flow once it reaches the ground and deliver it back to the energizer. The grounding system must be big enough, in relation to the energizer and soil moisture conditions, to be effective.
To create a ground system, you will pound a bunch of metal rods deep into the soil (see illustration here), wire their tops together with insulated wire and clamps, and attach the end of the wire to the negative (ground/earth) terminal of the energizer. If there aren't enough feet of correctly spaced rods for the size of the charge sent out by the energizer, and for the amount of moisture in the soil, the electric current can't find its way home easily and may flow weakly, impairing your fence.
Sometimes ground rods aren't enough to bring the charge back to the energizer, such as when soils are frozen or very dry. In that case you must add a "dead" or grounded wire next to the "live" or charged wires on the fence, close enough that an animal will be likely to touch both a live and a dead wire at the same time. The grounded wire is so-called because it is connected to the ground via a ground rod at the end of each stretch of fence. Instead of going through the animal to the nonconductive soil surface, the charge will go through the animal to the grounded wire and so to the attached ground rod. This will take the charge deep enough underground to find moist or unfrozen earth, allowing the charge to return to the energizer's ground rods.
Types and Uses of Electric Fence
Each type of electric fence is distinct and has its own place on a farm.
Permanent Electric Fence
Use. Best when you need to keep animals permanently away from plants, such as gardens and small fruit trees, or to create "cells" in large pastures that can then be further subdivided by temporary fencing for rotational grazing.
Setup. Utilizes deep-set metal or wooden posts and durable wires or woven wire.
Temporary Portable Electric Fence
Use. Ideal as an effective barrier for a day, a week, or a few seasons. Works well for rotational grazing and the temporary protection of such things as gardens, young trees, and beehives.
Setup. Uses short, lightweight posts that can be quickly pushed or pounded into the ground, and light plastic netting or light plastic wire with interwoven metal filaments that is quick to reel and unreel.
Use. Combines a physical with a psychological barrier. This is the fence of choice for property lines and anywhere you want to be extra sure no animals will get through. Not only is a perimeter fence of this type effective, but it also makes it simple to hook up a temporary fence anywhere on the property. Many graziers use combination fences to create permanent "grazing cells" on a larger acreage, which then can be easily subdivided with temporary fences for rotational grazing.
Setup. Extra-long "offset" plastic insulators are used to run one or more electric wires in front of a traditional wood, woven wire, or barbwire fence.
The gold standard in the "combination" category is electric high-tensile (HT) fence, which uses extremely strong, smooth wires strung tightly on deep-set posts. Some or all of these physically strong wires can then be electrified. Although it is the most effective fence for any purpose, unless you're experienced it generally requires professional installation with specialized tools and techniques. This book deals with do-it-yourself electric fencing, so HT fence won't be covered further.
Where Electric Fence Doesn't Work
There are four situations where electric-only fence is a bad idea or simply ineffective:
1. In animal-handling facilities — the chutes, headgates, pens, and crowding tubs used to herd and hold livestock for vaccinations, loading, pregnancy checking, and other operations that require animals to be restrained in close quarters. Crowded animals become stressed and naturally jostle each other. Adding an electrified wire to the situation, where inevitably someone will get pushed into it, can turn a quiet and controlled operation into a real rodeo. Use only physical barriers for handling animals in close quarters.
2. When the farmer or rancher is often not at home during daylight hours, or doesn't get around to checking the fenceline regularly. You can fix a short or a break before the animals take advantage of it only if you're around.
3. If it is illegal to use electric fence along a road or property line or across a waterway, as in some towns. Though it is legal in our rural township, I still think it is risky. Sooner or later an electric fence will fail, and then your animals may be loose on the road or in the neighbor's corn field. It would be far better to put an electric wire on the inside of a physical fence, or use just a physical fence along property lines where you need maximum reliability.
4. When separating newly weaned youngsters from their mothers, or breeding females from a breeding male. In fact, most physical fences are not totally reliable for this purpose either. The best approach is one or more of these:
* A lot of distance between the two groups of livestock (difficult for small operations)
* Isolation of the male in a very strong pen or building (traditional, but stressful for the male)
* A fence that is a physical and psychological barrier
Distance is my first choice, a dual-purpose fence my second; having both is best of all. The right combination fence can keep the bull from the heifers and the calves from the cows.
What Will Work for You?
The final decision on what type of electric fence to use where on your farm will depend on the specifics of the site, what's being protected or contained and for how long, your budget, and your personal preferences.
Use the worksheet on the next page to define your parameters and goals for your fence. The answers will help guide you in determining the size of energizer and types of fence components you'll need.
THE FENCE ENERGIZER
The energizer is the pulsing heart of the electric fence, not to mention the single most expensive, complicated, and confusing piece of the entire system.
The basic question everyone asks is, "What size energizer do I need to power the length of fence I have with enough of a charge to control the target animals?" Unfortunately, there is no simple formula that answers that question, since (as we discussed in the previous chapter) the energizer is only one of several variables that affect the potency of the charge.
You have to start somewhere, though, so here are two basic rules of thumb:
1. Do the math. Energizer size is generally given in joules (volts × amps × time), and many units also state how many miles of fence the energizer will power. As the first (and conservative) rule of thumb, figure that you'll need one joule for every 1.5 miles (2.4 km) of fence wire for easily controlled animals such as cattle and horses. For more difficult-to-control animals, including sheep and most predators, double the number of joules per mile.
If the ratio between the joules and the miles of fence given for a particular energizer is wildly different — say, a unit claiming to power up to 25 miles (40.2 km) of fence with one joule — it's unlikely that the energizer will put enough amps as well as volts on the wire at the far end to control any animals.
2. It's better to have too big an energizer than too small. If you have dry or frozen soil for all or part of the year, sandy or rocky soil, a lot of green vegetation touching the wires in some seasons, or rusty or knotted wires, you should certainly buy a bigger energizer than what is indicated by the simple 1.5 miles per joule guideline.
Combined with the checklist answers from chapter 1 (see Fence Planning ), these guidelines should give you a general idea of the size of energizer you'll need. Next there are the details of energizer types, power sources, and special features to consider, discussed below.
The hardest part of energizer shopping is distinguishing the good from the inadequate. There are many dozens of energizers on the market and many claims, but no universal standards, so in the section Telling the Good from the Not So Good we provide a few methods for separating the wheat from the chaff.
Finally, ground rods, lightning and surge protection, run-out wire, and fence testers are essential for getting the best out of your energizer. The grounding system is as important as the energizer in getting sufficient power on the fence. These items are discussed at the end of this chapter.
Sorting Out the Details
Since farmers first started electrifying fence wires, energizer research and development have centered on how to get enough of a charge on the fence to deter animals, but not so much as to injure or kill them when they touched the wire. As energizer technology advanced, not only have the units become safer and more effective, but they now offer more choices for power sources and added features.
Energizer Types: High and Low Impedance
Early energizers, remembered as "weed burners," utilized long pulse times and increasingly large charges to push the pulse all the way to the end of the fence. The problem was that this combination of inputs tended to start fires and kill entangled animals.
To reduce the number of grass fires and electrocutions, later models added resistors, or impedance, to choke the amps and volts down to a reasonable level. These "high-impedance" energizers are safer than the old weed burners, and effective for shorter fences and livestock with thinner coats, such as cattle and horses.
The charge isn't powerful enough, however, to reach to the end of a long fence or overcome the draining effects of a lot of vegetation touching the wire. And, since high-impedance energizers still use a relatively long pulse length, there remains a risk of heat building up enough at contact points to start a fire in dry grass, or to melt the plastic in temporary wire.
Low-impedance energizers, which now dominate the market, solved the drawbacks of the high-impedance types by shortening the pulse length from tenths or thousandths of a second to ten-thousandths. At that pulse length, even the high-amp, high-voltage charge of these energizers isn't long enough to start a fire or quickly kill an entangled animal (although caught animals can still die; it just takes longer). Removing the current-choking resistance, or impedance, also meant the charge was now powerful enough to bridge minor shorts.
These types of energizers can control almost all types of animals and power much longer fences. They also don't start fires, and have a much longer "off" time between pulses, making it easier for an entangled animal to escape.
A fence energizer can get its power from three different sources: an electrical outlet, a battery, or a solar panel that charges a battery powering the energizer.
Plug-in energizers provide the most power for the money, require the least maintenance (basically none), and are reliable in every situation except a power outage. You must install them inside a building or where they are well-protected from the weather. Units come ready to plug in to either 110- or 220-volt outlets; unless you have a really big operation, the 110-volt types will give you all the power you need.
Battery-powered energizers are portable and excellent for locations far from outlets. They range in size from dinky little 0.1-joule units up to 12 joules or so. In general you pay more per joule of power than for plug-in units. Follow the manufacturer's recommendations for battery type and be diligent about replacing or recharging batteries as they run down.
Solar-powered energizers have the highest up-front cost for the amount of power generated, don't come in larger joule sizes, and are slightly more complicated to move and set up. But like the battery-powered units, they're portable, and the power is free as long as the sun is shining.
Energizers that can run off either an outlet or a battery are a good choice if you will move your fence around among some locations with electrical service and some without.
Telling the Good from the Not So Good
Assessing the quality of an energizer can be a little tricky, not least because a good energizer can look bad if — as is so often the case — the ground system is too small, the ground is too dry, or the fence wire is covered with rust or green vegetation. In the store or catalog, however, energizers are best compared by looking at the numbers behind the joule rating.
Other Energizer Variables
In addition to size and power source, consider the following when shopping for an energizer:
The number of pulses per minute. Fewer pulses per minute means longer opportunities for an animal to slip through the fence without getting a shock. Sixty pulses per minute are effective for about any purpose; thirty a minute may not control some wildlife species. Forty-five pulses per minute may be a satisfactory compromise for battery- and solar-powered units to extend battery life.
Warranties and guarantees. A good free warranty indicates that the manufacturer stands behind its products.
Repair services. When a lightning strike, power surge, or wear and tear causes an energizer to fail, it will be essential to get the unit repaired or replaced quickly. Be sure to ask what service is available.
Bells and whistles. These include power controls that allow manual adjustment for pulse length and charge size, built-in lightning protection, indicator lights, and so on. Battery-charged units may include automatic nighttime "power-saving" modes. Some of these features may be worth it for the convenience; at a minimum an indicator light is very handy as a quick way of confirming that the energizer is on.
Excerpted from "The Electric Fencing Handbook"
Copyright © 2017 Ann Larkin Hansen.
Excerpted by permission of Storey Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of ContentsIntroduction
1 How an Electric Fence Works
2 The Fence Energizer
3 Fitting the Fence to the Animal
4 Permanent Electric Fence
5 Temporary Electric Fence
6 Planning and Building Your Fence
7 Rotational Grazing
8 Maintenance, Troubleshooting, and Repairs