Weather impacts electric fence
For many graziers using rotational grazing, the electric fence is a critical component of the total system. I know of examples where just one or two strands of electrified high-tensile wire serve as a perimeter fence along a road. The grazier is trusting in the electrical system and the prior experience and training the livestock have received to ensure the fence is not crossed.
In wet years, a lot of electrical fence systems can do an adequate job. Soils with good moisture ensure animals are well-grounded, and when a wet nose meets a wire, even if the voltage is not high, a good circuit is made. The resulting shock can convince an animal that the grass is not really greener on the other side.
However, in dry years marginal electrical fence systems may not maintain the desired voltage. Dry soils don’t provide the same grounding between animal and fence. Fences that might not be challenged in a year with plentiful forage may be tested in dry years with limited forage growth. During dry years we talk about slowing rotations down and even holding animals in one paddock as a sacrifice area until grass growth allows the rotation to be resumed. Can your fence keep your livestock from moving to where the grass really is greener?
Although many graziers have learned the basics of electric fencing, most can benefit from a review every now and then. The basic components of your electric fence system that should be evaluated are the fence energizer/charger, ground rods and the fence wire.
Match energizer and fence
In grazing schools you will hear that the fence energizer/charger is the “heart” of the electric fence system. The beginning grazier can avoid some frustrations by spending the necessary money for a high-quality energizer/charger. When the time comes to replace the current energizer/charger, this is not the place to cut budget corners.
Size the energizer/charger to handle your current fencing system, plus some room for growth. I know graziers who have significantly increased their electric fencing over the years. Sometimes the fence has increased as a result of expanded pasture acreage; sometimes the reason is more internal divisions as paddock numbers increase. Sometimes, it is both.
As the fence grows, graziers should check to make sure the energizer they have is adequate for the amount of fence they are asking it to charge.
Graziers should be checking their fencing to make sure it carries a voltage adequate to deter livestock from crossing. Figures I have heard thrown around regarding voltage levels and various livestock species include 1,600 to 2,000 volts for cattle, 3,000 volts minimum on electric netting for sheep and goats, and 4,000-plus volts on high-tensile fence for sheep and goats.
I also know of sheep and goat producers who maintain 7,000-plus volts on their fence.
The point here is to evaluate the charger/energizer as fencing needs grow and change, and either fence to include another charger/energizer in the system or add a larger charger/energizer to handle the increased fence. There are many ways to evaluate chargers/energizers, but one method is to look at output in joules.
Also remember that when a product is advertised by the miles of fence it can energize, it is for one wire. If multiple wires are energized, these must be added together. Four strands of high-tensile wire around a mile perimeter with two hot strands account for two miles of energized wire.
Remember ground rods
One component of the electric fence system that is sometimes overlooked is the ground rods. The full capacity of the charger/energizer will not be utilized unless a good ground system is in place.
In a dry year, it is critical to have the correct number of ground rods installed and properly spaced to help keep enough voltage on fences.
What is the correct ground rod system? A general rule of thumb says to install a minimum of 3 feet of ground rod per joule of energizer output capacity.
For example, if I have a 15-joule energizer, this requires 45 feet of ground rods. Generally, either galvanized or copper rods in 6- to 8-foot lengths are used. This energizer would require six to eight ground rods depending upon if a 6- or 8-foot ground rod was used.
Using coper rods
If copper rods are used, make sure to use a copper wire from the energizer ground terminal to the ground rod. If different metals are mixed, electrolysis can occur and the effectiveness of the grounding system is reduced, so stick with either galvanized or copper.
Ground rods should be driven in their full length, or if rocky soils don’t permit this, driven in at an angle so essentially the rods are lying in a trench. Ground rods should be at least 10 feet apart and 40 to 50 feet away from any other existing grounds. Ground rods should be tied together in a system, connected with wire between rods.
Try to locate ground rods in an area that is likely to stay moist. Northern exposures under building drip lines often work well.
In drought situations, it may be a good idea to water your ground rod areas to increase the effectiveness of your electric fence.
Finally, evaluate the fence itself. Remember that as the diameter of the fence wire decreases, there is more resistance to push electric current around the fence. Polywire is very handy stuff, but it should not be used to carry the charge long distances.
Use high-tensile wire to carry the charge and for perimeter fencing, and polywire to hook on to the high-tensile wire for internal paddock divisions. Voltage will drop in the fence as distance and amount of fence increase.
Also check to make sure the galvanized coating on the fence wire is intact. Rust is an enemy of electric fences.
Electric fence technology has allowed many graziers to more effectively utilize pastures and their management ability. Graziers need to periodically evaluate the energizer, ground rods and fence wire components of their electric fence system to ensure fences are operating efficiently and serving as effective barriers for livestock.
Lewandoski is with Ohio State University Extension in Athens County, Ohio.
This article published in the February, 2010 edition of THE FARMER.
All rights reserved. Copyright Farm Progress Cos. 2010.