Correctly Grounding an Electric Fence
- Improper grounding is the most common reason for electric fence malfunctions
- Install 90 cm (3') of ground rod for every joule of output from the energizer
- Ground rods should be more than 3 m (10') from each other
- Ground rods should be more than 23 m (75') from other grounds, waterlines, or utilities. Ontario One Call can help you locate publicly-owned infrastructure: 1-800-400-2255 or www.on1call.com. A private locator can be hired to find other buried infrastructure.
Improper grounding is the most common mistake that causes an electric fence to malfunction. Understanding electricity and all the jargon that goes with it can be a challenge. Luckily, thinking about water is often a great way to imagine electricity, so I'm going to draw some comparisons between electricity and water in this article.
Why do I need to ground my electric fence?
Just like water, electricity has a current. Electric current is a steady flow of electrons. Much like water runs downhill, electrons move towards a positive charge such as the soil (think lightning strikes), or the earth terminal on the fence energizer. Metal and water are good conductors of electricity because they hold electrons loosely and are relatively dense, which enables electric current to flow through them.
Electric current needs a circuit of conductive material to flow. A properly constructed electric fence is a potential circuit. Electric current is sent from the energizer through the fence wires. Ground rods are installed and wired back to the energizer. When an animal touches the fence, the circuit is closed, allowing the electric current to flow from the energizer, through the fence wires, through the animal, into the soil moisture, to the ground rods, and back to the earth terminal on the energizer.
Building an electric fence means creating a potential circuit; one that closes properly when something touches the hot wire and the soil at the same time. An electric fence is a psychological barrier: cattle learn not to touch the fence because the shock is unpleasant. Untrained animals or a non-electrified fence may enable livestock to go right through the fence, because it is not physically strong enough to stop them. To be effective, both the fence and the ground system must be installed so that they become a circuit, and a practical way to contain cattle.
How do I install a ground system?
Ground rods made of either copper or galvanized metal are available. While copper is more conductive, it also corrodes faster. Corroded metal is not a good conductor, and can prevent the circuit from closing. Galvanized rods will last longer than copper ones because they are protected from corrosion. Ground rods should stick out of the soil 10 - 15 cm (4 - 6"). Ground rod clamps have been designed to conduct electricity from the rod to the return wire, and work better than home-made clamps or those designed for a different purpose. Double check that brass clamps are used with copper rods, and dissimilar metal (non-corroding) clamps are used with galvanized rods. Mixing metals can make components corrode faster.
To ensure ground rods come in contact with enough soil moisture to complete the circuit, the best practice is to install 90 cm (3') of ground rod below the water table for every joule of output provided by the energizer. The water table is the level below which the ground is saturated with water, and the depth can vary greatly depending on location. Where the ground is dry or the water table is low, this may not be possible - dumping a bucket of water on each ground rod at regular intervals can help maintain contact. The length required can be divided between multiple ground rods but these must be spaced at least 3 m (10') apart, otherwise they act like a single ground rod.
In areas with a very shallow depth to bedrock, it may not be possible to bury rods deep enough to properly ground the fence. Some farmers have had success in these situations with the ground plates used to ground houses. These can be found at many hardware stores.
In addition to spacing out multiple ground rods for the fence, ground rods also need to be more than 23 m (75') away from any other grounds, waterlines, or utilities on the farm. Ontario One Call offers a "call or click before you dig" service, allowing landowners to request infrastructure location to identify where publicly-owned utilities are buried. Ontario One Call needs five business days' notice, but will arrange for someone to come out to the farm and identify buried infrastructure that may interfere with the fence grounding system. Ontario One Call can be reached at 1-800-400-2255. Not all owners of buried infrastructure are registered with Ontario One Call, and privately-owned companies may need to be contacted individually. A locator service can be hired to locate these utilities and any infrastructure running between farm buildings, as these are generally privately installed and not covered by Ontario One Call.
Why do some electric fences contain ground wires?
In Ontario, climate affects the design of electric fences. If the earth is frozen or snow-covered, it can be difficult to achieve electrical contact; snow contains a lot of air, and ice holds onto electrons more tightly than liquid water. Often an animal touching a hot wire will not complete the circuit. This has led to many fences being built with alternating hot and ground wires, called a ground-return system. Hot wires are connected to the output of the energizer, while ground wires are connected to the ground rods. If an animal touches both the hot and ground wire at the same time, they close the circuit and receive a shock. This design keeps electric fences working throughout the year.
With a ground-return design, it is common for ground rods to be installed along the fence every 400 m (1300') to improve the grounding system.
How can I tell if my fence is grounded properly?
A volt meter touched to the ground rods should read less than 400 V. If the reading is greater than 1000 V, another ground rod should be added to the system.
Another sign that the fence is not grounded properly is stray voltage. Stray voltage is a difference in electric potential between two places that should not be different. With improperly grounded electric fences, it is most common to hear a ticking sound over a landline telephone, have problems maintaining an internet connection when the energizer is on, or interference with radio or television reception. Occasionally, poor grounding may send current through other metal items or water lines; if cattle are refusing to drink, check that their trough hasn't been accidentally electrified.
Most problems are caused by not having enough ground rods, installing ground rods in bad locations, or having loose or corroded ground rod clamps.
For more information:
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|Author:||Christine O'Reilly, Forage and Grazing Specialist, OMAFRA|
|Creation Date:||26 July 2018|
|Last Reviewed:||26 July 2018|