Electric Fencing Basics

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Electric fencing is ideal for grazing or pasture management by containing animals on a selected area of pasture or crop. It also may be used to protect gardens and landscapes from animal damage.

In 1938, the first electric fence was developed in New Zealand by Gallagher. Since that time, electric fencing systems have made farm and ranch life easier. Today, both permanent and portable electric fencing products are used all over the world.

Basics of electric fencing

Permanent electric fencing is economical, easy to install and easy to maintain. Temporary electric fencing provides an effective temporary barrier for short-term animal control and rotational grazing. Electric fencing is:

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Fig. 1: Open circuit, no current flowing

Fig. 2: Closed circuit, current flowing

Safe: Animals remember the short, sharp but safe shock and develop respect for the fence

Easy to install: An electric fence takes less than half the time to build compared to traditional fence systems

Durable: A non-electrified fence experiences constant wear and tear under stock pressure. Because your animals learn to avoid an electrified fence, your fence will last longer and remain in good condition

Economical: Electric fences cost less than 50% of traditional non-electric fences

How does an electric fence work?

Electric current (Amps) only flows when a circuit is completed between a positive and negative terminal.

In Fig. 1, the current cannot flow from the positive terminal to the negative terminal because the switch is open.

In Fig. 2, the switch is now closed, allowing the current to flow from the positive terminal through the light bulb (lighting the bulb) to the negative terminal.

Fig. 3: An animal standing on the ground and touching the electrified wires will complete the circuit

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An electric-fence circuit is made on a larger scale. The energizer fence terminal (positive) is connected to the insulated fence wires, and the energizer ground terminal (negative) is connected to galvanized metal rods driven into the ground.

The same “circuit completion” (Fig. 2) is necessary before the animal gets a shock. An animal standing on the ground and touching the electrified wires (Fig. 3) will complete the circuit like the closed switch in Fig. 2.

For example, a bird sitting on the wire will not receive a shock (Fig. 4). It is not touching the ground so the circuit is not completed. A person wearing insulated footwear will only receive a small shock because all the current cannot pass through the insulated soles.

Dry, sandy or pumice soil is a poor conductor of electric current, so it is a good idea to add a ground (negative) wire into the fence. The animal must touch both a hot wire and ground wire to feel an effective shock (Fig. 5).

Choosing the right energizer

Once you have decided what type of electric fence you want for your property, you will need an energizer, or fence charger, to power it. The correct energizer size for your property is determined by the type of animal to be fenced, distance of fence to be powered and the number of wires in the fence.

Fig. 4: A bird sitting on the wire will not close the circuit to receive a shock

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There are two types of energizers:

• 110v powered — these are energizer units which are plugged into a 110v power supply.
• Battery/Solar powered — these are energizer units that can be left out in your pasture and require a battery to run them. Two batteries can be rotated on a regular basis or a solar panel can be an effective means of continuously charging your battery.

Steps to good grounding

Grounding is perhaps the most neglected component of many fence systems. Three ground rods — 6 feet (ft.) deep and spaced 10 ft. apart — is a minimum recommendation. Never attach copper to steel. Electrolysis can occur and result in corrosion, which weakens shocking power. Use galvanized ground wire and grounding rods to avoid this problem.

Consider that most energizers use galvanized or stainless steel terminals — not copper. Think of your ground system as an antenna that gathers electricity to deliver the shock to the animal. Modern satellite receivers can tune in to more television channels than the “rabbit ear” antennas of the past. A hose clamp holding a piece of copper wire to a rusty T-post has been the weakest link of many electric fence systems.

Fig. 5: With a ground wire, the animal must touch both a hot wire and ground wire to feel a shock

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Safety

There is a misconception that dry vegetation touching an electric fence can cause fires. This is extremely unlikely. To create a short, vegetation needs to be damp or green; therefore, dry vegetation will not ignite. Once vegetation dries out it becomes non-conductive, meaning any short created disappears.

The only conceivable, but still unlikely, scenario where an electric fence could start a fire is when a wire shorts to a grounded metal object, such as a steel post or wire where insulators have broken, in the presence of abundant dry vegetation. This scenario is unlikely to occur in practice, and even less so on a well-maintained fence. Producers with fences on steel posts or using earthed wires are advised to ensure the live wires are well insulated and the fence is clear of vegetation. If these factors are of concern then on days of severe or above fire risk, consider switching the energizer off.

Editor’s note: This article and figures are from Gallagher.