How does an electric fence work? Learn about portable electric fencing from electron flow, conducting polymers and pulsed energy.
Electric fencing has come a long way since Mark Twain described the concept in his 1889 book, A Connecticut Yankee in King Arthur’s Court. And though Twain’s use of the technology didn’t have anything to do with managing animals (of the four-legged variety), one wonders whether early electric fence inventors were influenced by the Connecticut Yankee’s shocking ingenuity.
How Does an Electric Fence Work?
Electric fences made their first mainstream appearances in the United States and New Zealand in the 1930s – those applications were almost exclusively agricultural. Today, electric fence technology includes portable electronic solutions for managing domestic animals and wildlife that are economical, effective and easy to move around.
Shocking memorable experiences
Portable electric fencing doesn’t offer much in the way of a physical barrier for keeping animals in or out, but it does become an effective psychological barrier once animals learn the shocking consequences of an encounter with a conductor. As a psychological barrier, one wouldn’t want to use portable electric fencing to secure the farm’s perimeter (except in emergencies), but with trained livestock (and wildlife), portable electric fences will give you the most flexibility for managing animal activity on the inside. Training your animals can be as easy as cross-fencing their current paddock with a portable electric fence for a sufficient length of time that they learn to avoid it altogether and never break through.
Electrons flow
To be effective, portable electric fences must deliver a powerful shock every time an animal comes into contact with a conductor, or close enough that a high-voltage arc forms between the animal and the conductor (think touching a metal doorknob in winter). That shock relies on an energizer, which sends a pulse of high-voltage electrons into the fence’s conductor(s) and a functioning grounding system, facilitating the electron pulse’s movement into and through the animal. When the fence system is set up properly, the animal is always grounded, and when the critter gets too close to a conductor, the shock will be memorable but harmless. If the ground is faulty, the animal may get tickled or avoid getting shocked at all – much like the instance where a farmer with heavy, dry, rubber boots on his feet avoids receiving a painful shock when encountering an electric fence.
To keep the electrons in the conductor from routinely finding their way to the ground, you need to suspend them with the help of easy-to-install posts – many of these are easily pushed into the ground or have a step integrated into the design so you can use your body weight to set the post. Others are designed to use special lightweight post drivers or hammers for setting. Posts for portable electric fencing are usually constructed of insulating polymers, fiberglass or steel. Steel posts are conducting, so they need to be coated with an insulating material, or you need to install insulators on them to avoid shorting out the fence. You will also want to insulate the conductors from any permanent fences you might include in the overall animal control plan.
Conducting polymers
Light metal wires make effective portable electric fence conductors, but they are difficult to see, harder to wind onto spools and heavier than many alternatives. Twines twisted from ultraviolet stabilized polymers and fine metallic threads (polywire) are light and easy to spool and un-spool, with the trade-off being that they won’t carry as much shocking potential for the same distance as solid wire. Specialized braided wire/polymer lines and ribbons generally fall between the twisted conductors and solid wires with regard to shock-carrying capacity, and they have the advantage of being resilient to numerous spooling and un-spooling cycles.
Most temporary electric fencing systems rely on a single conductor, but three or more individual conductors may be used depending on the species of animal you are trying to control. For example, hogs respond well to a pair of conductors located at roughly 6 inches and 18 inches off the ground. Cattle will respect a single conductor located at about 32 inches. Sheep and goats will generally respect four-conductor fences (fewer conductors are needed in low-pressure situations), but poultry and high-density groups of sheep and goats might be best controlled with a net-type conductor system.
Electric netting is available in many different heights with a lot of variation in horizontal and vertical spacing. Generally speaking, netting is made with conductors for the horizontal lines and insulating strands for the verticals. Although it’s heavier, more cumbersome and more expensive, electric netting makes an excellent temporary fence to confine difficult-to-contain animals while keeping out more persistent predators. Netting is also more effective at keeping rabbits and other garden marauders at bay than many multiple-strand conductor systems.
Pulsed energy
If the conductors are the arteries of the portable electric fence system, then the energizer is most definitely the heart. This mystery box takes 110-volt alternating current, or something in the vicinity of 12-volt direct current (solar/wind battery or stand-alone battery), and converts it to low amperage bursts of high-voltage electricity. When properly connected to a portable electric fence and ground, the energizer sends high-voltage pulses into the conductors at short and regular intervals. Energizer output is generally expressed in joules, an energy term that relates to a fixed amount of work. One joule is the amount of work it takes to generate one Watt of power for one second. Still confused? That’s OK. When it comes to portable electric fencing, all you really need to know is the joule output rating of an energizer (a low-impedance model for most situations) and how many miles of conductor you wish to energize for any given environment. It’s actually a little more complicated than that, but good electric fencing companies have knowledgeable personnel who can help you make the right choice – especially when it comes to the shape of the pulse and the impedance level of the energizer.
Electrons working for you
Portable electric fencing is useful for everything from temporarily closing a breech in a perimeter fence caused by your neighbor felling a tree on it and not telling you, to strip-grazing your cattle through the winter on stockpiled standing grass, to protecting your precious sweet corn patch from ravenous raccoons. Portable electric fences can also keep your pastured poultry safe from four-legged predators and your pigs from tilling the garden when the tomatoes are just
beginning to ripen.
I’ve used portable electric fencing for everything from an emergency pasture gate, pasture subdivision fences and management-intensive cattle grazing, to pastured poultry, pig control, garden protection or you name it. Folks with fruit trees and large market gardens employ portable electric fencing to protect large orchards and 40-acre vegetable patches from deer and other wildlife damage. Hunters use portable electric fencing to control wildlife access to food plots and animal movement through their hunting properties.
Next time your animals wind up precisely where you don’t want them, rather than despair at the massive and expensive enterprise of installing a permanent wire fence, head to your local or online portable electric fencing dealer and procure a few spools of polywire or braided conductors, a couple of reels to keep track of those conductors, an energizer, an assortment of insulating handles and 50 step-in posts – you will be shocked at how easy the fence goes up, comes down and can be moved around.
Hank’s Osage County, Kansas, farm holds enough livestock to keep several portable electric fences, and at least four energizers, gainfully employed at any point in time.
Hank Will raises hair sheep, heritage cattle and many varieties of open-pollinated corn on his rural Osage County, Kansas farm. His home life is a perfect complement to his professional life.
