Rural Electric Fence Training Manual
- Basic electrical terms
- How/why an electric fence works
- Series and Parallel circuit’s
- Fence/Gate construction
- Energizer & Accessories Selection
1. Basic electrical terms
When talking about electricity we need to understand a few terms and definitions, below is a list of words or phrases we will be using, which may or may not make sense to you.
- Flow of electricity: This is the movement of electrons along a conductor/wire, this can be compared to the flow of water through a hose. Just like water it has a volume and pressure to create the power to do work. So does electricity.
- Current: The volume or the amount of electrons flowing, is the current. This is measured in Amps.
- Volts: The pressure or force that electricity is under is measured as Volts. The voltage between two points is measured as a potential difference between those points.
- Resistance: This is the nature of an object to resist or prevent the flow of electricity. This is measured in ohms.
- Circuit: This is the path that an electric current travels on. Current will flow in a closed circuit but not in an open circuit.
- Watt: The watt is a method of measuring the rate of energy transfer or can commonly be called power
- Joules: The standard international unit of energy equal to one watt for one second
- Battery: this is a device that stores chemical energy and converts it to electrical energy. The flow of electricity is from the positive to the negative terminal.
- Relay: these are electrically operated switches that turn on and turn off the connected devices by receiving electrical signals.
- A/C: Alternating current is the type of power we get in our homes, this is called alternating current because it changes direction from negative to positive constantly as it flows.
- D/C: Direct current is the type of current supplied by batteries and its flow is from one terminal direct to the other, it does not change direction.
- Energizer: An energizer is an electric device used to create the high voltage pulse to be sent down the hot wires on an electric fence. This is done with a control circuit, capacitors and output transformers
2. How an electric fence works
- An electric fence is a barrier that uses electric shocks to deter people and animals from crossing a boundary.
- Most electric fences are used for agricultural fencing and other forms of non-human animal control, although they are increasingly also used to protect commercial & residential areas.
- Electric fences are designed to complete an electrical circuit when touched by an animal or person.
- A component called an energizer converts electrical power into a brief high voltage
- One terminal of the energizer releases this electrical pulse along a connected bare wire about once per second.
- Another terminal is connected to a metal rod implanted in the earth, called a ground or earth rod.
- An animal touching both the wire and the earth during a pulse will complete the electrical circuit and will conduct the pulse, causing an electric shock.
- The effects of the shock depend upon the voltage, the energy of the pulse, the degree of contact between the recipient and the fence and the ground (earth) conductivity.
- The shock can range from barely noticeable to painful.
3. Series and Parallel Circuits
There are two basic ways in which to configure an electric fence: series and parallel
- When using a series connection the fence wires are connected end-to-end in a line to form a single path through which current can flow:
- When using a parallel connection, all the fence wires are connected across each other’s leads. There are many paths for current flow, but only one voltage across all components:
Series wiring = higher sensitivity but higher resistance so is used on security fences.
Parallel wiring = lower resistance but less sensitivity making it more suitable for animal control
Your electric fences performance will be determined by how well your earth grid performs. A good earth grid is the foundation of a good electric fence, there are many different ways to configure the earth grid .The most important question we need to answer is, why do we need the earth circuit? To understand why we need good earthing we need to understand its two functions.
- The first job of the earth system is to ground out one side of the energizers output transformer. As we know voltage is measured as a potential difference between two points, The most effective way to ensure a good shock is to keep the potential difference (voltage) between the two ends of the output transformer as big as possible. The easiest way to do that is to make one side ZERO, (ground it) hence we install the earth rod close to the energizer.(but this must be 10m from any other existing electrical or communication earthing)
- The next function is even more important, When an animal/person touches the hot wire, in order for them to feel the shock they need to complete the circuit. Their body completes the electrical circuit between the live and the earth,(both sides of the output transformer) the current will flow through the wire, through the person/animal, into the ground and all the way back to the earth spike.(As seen in the following diagram )
- The down side of using only the ground to complete the circuit is that its resistance or conductivity changes depending on its make-up, (clay conducts electricity better than rock) and water levels contained .The ground conductivity will change throughout the year. It is affected by rainfall as water conducts electricity an electric fence installed in the wet months may perform faultlessly, however be ineffective in the dryer months of the year.
- The answer to the problems discussed above is called the Fence return System .As can be seen in the below drawing the operation for the fence is the same, with one exception, the shock is returned to energizer via an earth wire on the fence .This is a quicker and more reliable return method so this will increase the shock felt.
- The fence return system is a very important part of the modern security fence as it will provide a more reliable shock ,stops people diving through a freestanding fence and will “short out” the high voltage circuit when cut. The hot wires are under tension and will return to a bundle when cut thus completing the circuit and dropping the voltage and setting off the alarm.
- Earth stakes must be driven the whole way into the ground .(Do not cut short)
- Earth stake must be a minimum of 10m from any existing electrical or communication earthing.
- Position earth stakes in permanently moist areas if possible.
- Fence return system is required for consistent earthing. Ground return earthing is only effective in moist soil.
- On security fences connect the posts and protective mesh to the earth system at regular intervals.
- Additional earth spikes may be required along the fence line, not only at the energizer.
- Use joint clamps to ensure good contact between wires and earth spikes.
- An effective earth grid is at least 3 earth spikes installed at least 3 m apart.
Check earth grid regularly as brush cutters and other landscaping work can remove or damage the wiring connecting earth spikes to the fence.
Testing the Earth grid.
- Connect the end of your live wire to earth by hammering a metal stake into the soil, and connecting this to the live fence wire.
- Using an electric fence volt meter or a JVA Electric Fence Fault Finder (do not use a standard multi-meter) check what the voltage is at the earth terminal of the energizer.
- In general you should see a reading less than 300 volts (0.3kV).
- If the voltage is higher than 300v you will need to increase the efficiency of the earth grid by installing additional earth spikes.
- For particularly poor earth conditions (sand, peat, gravel, very dry soil, snow or frozen ground) it is possible to increase the earth efficiency by: Increasing the number of earth spikes or running earth return wire on the fence line and connecting it to spikes at regular intervals.
- See separate ‘fault finding’ manual for more information.
4. Fence/Gate Construction.
- The fence should be well constructed and the construction method should suit the landscape it is installed in.
- Visibility is important! A cattle spec fence will stop most horses if they see it or are used to it .However a horse in a panic is likely to try jump the same fence and can be hurt in the process. Always design the fence around what you are wanting to contain.
- The distance between the posts and the intermediate posts will affect the cost considerably, this should be discussed with the client.
- The function of the fence needs to be discussed and taken into account in the planning stages. Security fences need to perform different tasks to a deer fence, while the principles of operation are the same the looks and costs associated with these two designs are considerably different.
- The positioning of the energizer in relation to the fence line will affect the cost and performance of the system.
- For animal control we recommend a hot wire at head and chest height, as well as an earth wire in between.
- Plan gateways and paddock entry points with the terrain and functionality of the completed fence in mind.
- Use approved conduit for all under gate cables, bury the cables deep enough to not be damaged by plant and machinery that may go through the gateway.
- Always configure gates in such a way that the power is disconnected when the gates are open or in the process of opening.
- Take a look at where handles are positioned on the gates, how likely is accidental contact with the hot wire going to be while handling the gate
6. Energizer & Accessories selection
Once again the type of energizer will depend on the function you want to perform.
- Mains or battery powered.
- Battery units have external batteries
- Different size/power units available.
- Battery units can be connected to solar systems.
- Normally wired in parallel.
- Stand-alone operation.
- Small compact all in one solar units available.
- Separate alarm/monitoring devices available
The modern range of JVA rural energizers are Wi-Fi compatible, this sounds complicated but in reality is very simple.
The full instruction manual is in the box when shipped.
This gives the owner the ability to turn on or off the energizer via a cell phone, as well as see the output voltage, joules and the battery input voltage
There are many accessories that can be added to make your fence function better and give you the owner/operator more information. Most of these are more suited to the security sector however some are useful in both situations.
- Cut out switches: These are used to cut power to the fence or sections of the fence. Often connected between energizer lead-out cable and fence wire to cut power to the fence. Also Connected along fence line to cut power to sections of the fence
- Line clamps: Clamp fence wires together or use to join lead out cables to live wires. These prevent arcing and unravelling as can commonly occur with twisting wires together. Suitable for most fence wire types.
- Warning signs: Electric fences are required by Australian/New Zealand Standards to have warning signs fitted at regular intervals where the public could potentially come in contact with the fence. This means along a road frontage or driveway. These bright yellow signs can be clipped or tied to the fence wire.
- Lightening diverters: These provide protection for the Energizer on both the Feed and Return fence wires ensuring a lightning strike on, or near the fence, is safely diverted to Earth. Its two stage protection can withstand a lightning surge of up to 2000 Amps limiting the voltage to the Energizer to an acceptable 15kV.
- Offset brackets /bobbins: Perfect for mounting an electric wire inside an existing permanent fence. Usually a single electric wire is all that is needed to prevent livestock from pushing through a fence or rubbing against it. Also known as outriggers. Double offsets are available for areas with earth problems.