recommendations for erecting permanent electric fencing,
problem-solving for ineffective fences,
what to think about when choosing components for a well-performing electric fence and
instructions for the installation and operation of electric fencing
The principles of electric fencing
The following information answers two questions:
- Why should you choose wire with good conductivity?
- Why should you always check the earthing?
The current in an electric fence circuit must pass through three parts in order to close the circuit. These are the wire, the animal and the earth.
This can be described in simple terms as follows:
The current passes from the energizer into the wire. The animal makes contact with the wire and conducts the current into the ground. The current in the ground returns to the energizer through the earthing rod. The circuit is closed.
Each rectangle symbolises the resistance (R) of the part in question, i.e. the resistance of the wire, earth and animal/vegetation. The energizer registers the total resistance and adapts the power accordingly. The voltage from the energizer is spread across the three resistances, depending on their sizes.
If the wire’s resistance is high, it leads to a large voltagedrop. Near the energizer the voltage can be 5 000 V, but a little further along the wire the voltage is only 2 500 V.
If wire with good conductivity (low resistance) is used, the voltages near the energizer and along the wire are almost the same, i.e. 5 000 V and 4 800 V respectively. This is because the resistance of the wire is so low.
The resistance of the animal/vegetation can vary between very high (no vegetation, no animals) and very low (dense vegetation, animal touching the fence). This is difficult to know in advance. It is important that the energizer is able to detect what is happening in the wire. This is achieved by ensuring that animals and grass are the factors causing the highest resistance in the fencing system. To do this, the total resistance of the wire and earth must be as low as possible.
The resistance of the ground must therefore also be low. This is achieved by having numerous earthing rods with good, large ground contact. The only way of knowing whether the earth resistance is high or low is to measure it using a digital volt-meter (DVM). If the resistance is high, there is a large voltage-drop across the earthing rod, i.e. the DVM displays a high reading of >0.3 kV. If the resistance is low, the DVM displays a low reading.
The most important prerequisite for a functioning electric fence is to keep the resistance of the wire and earth as low as possible. The resistance from the animals and vegetation will then always be at its highest. The energizer will thus detect changes in the load due to more vegetation, change its power point and maintain high voltage.
An electric fence is a system built up from a number of different components. For the system to work, it is very important that each component is good quality and compatible with the rest of the system. We describe the essential components and their properties below:
Electric fence energizer
The first thing to decide is whether to have a battery or mains powered energizer. If possible, choose a mainspowered energizer because they have lower running costs.
When choosing an energizer, the main things to consider are the height of the lowest wire above the ground and the length of the fence. For sheep, the choice is therefore a powerful energizer because the lowest wire is not more than approx. 30 cm above the ground. For horses, a relatively low-power energizer is sufficient because the bottom wire is seldom lower than 60 cm. For the same reason, choose the most powerful energizers for permanent electric fences. They are usually long, with a lot of vegetation. The more powerful the energizer, the greater the safety margin in unforeseen events such as a tree branch touching the fence or animals unused to an electric fence coming into contact with it.
Choose the wire depending on the type of fence to be erected. For moveable fences, always choose lightweight polyester wire or tape because the fence will be moved several times during the season. Note that it is important to use wire/tape with low resistance. The wire’s resistance in Ohm/ m is stated on the roll. For example, 0.2 Ohm/m means very good electrical conductivity, whilst 5 Ohm/m is poor conductivity. Furthermore, choose high contrast wire/tape. For example, black and white wire/tape has considerably higher contrast and visibility than orange wire. For permanent fencing, use only pre-stretched triple-galvanized steel wire. The galvanizing on this special quality steel wire is three times thicker than on ordinary steel wire. Also, this wire does not stretch when exposed to weather and wind.
The choice of posts also depends on the type of fence being erected. For movable fences, choose lightweight fibreglass, plastic or spring steel. These lightweight posts are easy to carry and very easy to erect. Remember to use timber posts as corner posts for moveable fences too. Only pressure-treated pine posts are strong enough for permanent fences.
Good insulators are required to insulate the wire from the post, unless lightweight posts fitted with insulators are used. Avoid small-diameter reel insulators with high-power fence energizers. It is important to keep the staple that fixes the wire to the fence well away from the insulator and to have ample separation between the wire and the post. Ring insulators are excellent. They keep the wire and the post well-separated, and are very reliable against creeping currents. Tensulators are suitable for end and corner posts. They also act as wire tensioners. They are first-rate insulators because only the nylon wire comes into contact with the post. Installing tensulators is quick and easy. The product is also 100 percent rust-free (only plastic and stainless steel are used).
This is the most important and perhaps most overlooked aspect of an electric fence. Remember that the electric fence will not work if it is inadequately earthed. With small battery-powered energizers, use one one-meter earthing rod. With our most powerful mains operated energizers, use at least five one-meter earthing rods. It is important that the earthing rod is set in firm ground in a damp place and that the entire earthing rod goes down into the ground. The cable to the earthing rod must be properly screwed into the rod.
Good earthing is very important for getting maximum capacity from the fencing system. Use min. three earthing rods placed at three to four metres between each other. For best results, the rods should be placed in humid ground.
How to check earthing
- Short-circuit the fencing by leaning an iron pole/rod against the fencing wire approx. 100 m from the energizer.
- Measure the voltage between the earthing and the ground
- If the measured voltage is higher than 300V (0,3 kV) the earthing is insufficient and needs to be improved with one or more additional earth rods
Recommendations for erecting permanent electric fencing
Main points for erecting permanent electric fencing:
- Plan the most suitable position for the fence. In woodland and pasture, it is essential to take the terrain into consideration and exploit it to obtain the most effective fencing possible. Try to keep lines as straight as possible. It is also possible to achieve slightly curved lines by using 60 mm intermediate posts. When erecting permanent fencing around arable land, it is important that the fence is not too close to the area concerned. There must be enough room to turn a tractor comfortably.
- Clear vegetation and brushwood along the line of the fencing. Remove small undulations.
- Plan the positions of corner and end posts. Use a post borer to make holes for the corner posts and erect them.
NOTE : This is the most critical work on the entire fence. The posts must be set one meter into the ground and surrounded by gravel or sand. Alternatively, a corner can be braced if the ground is shallow and rocky.
- For entirely straight lines, stretch a wire between the corner posts to indicate where the other fence posts should go. If the line is somewhat curved, the posts must be erected by eye. In these circumstances it is an advantage to have two people, which makes it easier to take sightings.
- Erect the fence posts at approximately six-meter intervals. If the ground is very uneven, the distance between posts must be reduced. If it is completely flat and level, the distance can be increased to seven to eight m.
- Mark the required wire height on the corner and fence posts. The height and number of strands of wire depend on the type of animal being enclosed.
- Fit the insulators.
- Unreel the wire and lay it in the insulators. Use tensulators, insulated tubes or corner insulators on ends and corners.
- Tension the wires using tensulators or wire tensioners.
- All wires in each section must be connected together in at least one place. Use wire connections. Erect the fence in sections. A section is the length of the wire before you cut and tension it. A section must always begin and end with an end or corner post. It is seldom appropriate for sections to be longer than around 400 m. On totally flat and level areas, sections can be long. Where there are many corners, the sections must be shorter.
- The energizer is always fitted indoors where someone will pass it every day. Good quality earthing and leadout cable must be used for both the earth and the fence terminals.
- Earthing is done in a damp place near the fence, not along drained building walls. Begin with at least three earthing rods. In the majority of cases, up to six to eight earthing rods are needed for a permanent electric fence.
- Check the earthing. With very long fences, it may be necessary to fit an earth wire to the fence. Staple a steel wire 15 cm above the ground and connect it to an earthing rod every 400 to 500 m.
Recommended wire heights and numbers of strands for different types of animal
||Number of strands
||1 to 2
||50 + 90 cm
||2 to 3
||60 + 90 + 120 cm
||2 to 4
||30 + 50 + 70 + 90 cm
||25 + 50 cm
||3 to 4
||30 + 50 + 70 + 90 cm
||3 to 4
||30 + 70 + 110 + 150 cm
||90 + 150 + 170 cm
||20 + 40 + 60 + 90 + 120 cm (or 25 + 45 + 70 + 105 cm)
How to design a gate
To keep the fence live when the gate is open, the fence on both sides of the gate must be connected to each other through an earth cable. With this construction the gate will not be electrified when it is open.
Problems with an ineffective fence
These five fault-finding points below will help with locating the cause:
- Check that the electric fence energizer gives the output voltage stated in the product literature. Disconnect the fence and earth. Use a digital volt-meter to measure it directly across the output terminals.
- Check all joins in the wire, particularly if polyester wire or tape has been used. With polyester tape, tape joints must be used to obtain good joins. With polyester wire, the feeds must be twisted together after the wires have been fastened together.
- Check the earthing: Short-circuit the fence approximately 100 m from the energizer by inserting a rod in the ground and leaning it against the fence. Return to the earthing rod and touch the rod and the ground. If you feel a real shock, the earthing is not good enough and must be improved by using more earthing rods. Earthing rods should be inserted in damp ground and at some distance away from buildings, so that the rod is not in sandy infill by the wall. Rods are positioned at approximately 1.5 m intervals. Use screw connectors to connect the earthing rods. Instead of grasping the earthing rod, you can use a digital volt-meter. The meter should not show a reading greater than approximately 300 V between the earthing rod and earth.
- Check the insulators. If you hear an insulator ticking or you can measure a voltage drop at the insulator, you must change to a higher-rated insulator.
- Check that there is not too much vegetation and that there are no branches lying against the wire. This is particularly important with lower power energizers.
Instructions for the installation and operation of electric fencing
NOTE: The instructions below are according to Swedish regulations. Please check your own country's regulations. Under certain conditions electric fencing can constitute a fire risk.
E1. Electric fencing must be installed and used in such a way that it does not cause any danger to people, animals or its surroundings. As far as is reasonably possible, it must be out of the reach of children and not subjected to mechanical damage or unauthorised tampering. Insofar as the following requirements are additional to, but not in conflict with, regulations issued by the national authority responsible, they are valid for the installation and operation of electric fencing and its devices.
E2. Electric fencing must not be fed by more than one device. Electric fencing with one wire must be fed by only one fence circuit on the electric fencing device. Electric fencing with several wires can be fed from different fencing circuits from the same electric fencing device, provided that only one fencing circuit is used to feed an individual wire.
E3. For two separate electric fences, the distance between the fencing wires and the distance between the connecting wires must be at least two m. If the space between is to be fenced, this must be done using electrically non-conductive material.
E4. Barbed wire must not be electrified in electric fencing. Non-electrified barbed wire must not be used in combination with single or multiple wire electric fencing.
Advice: The horizontal separation between an electric fence and other obstacles to movement running parallel to the fence should not be less than two m, in accordance with the Swedish Electrical Safety Administration’s and the Swedish Board of Agriculture’s assessment, in the light of the regulations in item E1 and accidents that have occurred.
E5. An electric fence, or parts thereof, installed along a public road or footpath, must be identified using warning signs fixed securely on posts or fixed securely to the fence wire at frequent intervals. The size of the warning signs must be at least 200 x100 mm. The background colour on both sides of the warning sign must be yellow. The lettering on the sign must be black and in the form of the symbol in accordance with Fig. E1 or include the following warning: “beware – electric fence”. The inscription must be permanent and all letters must be at least 25 mm high.
E6. If it is necessary to cross a public highway with a fence wire or lead-out feed, the authority concerned must be informed. In all cases the vertical separation between the wire and any part of the roadway must be at least five m.
E7. Where electric fencing crosses a bridleway or other public footpath, a non-electrified gate must be included in the fence at this point, or there must be a crossing using stiles. At a crossing like this, the adjoining fencing wires must be equipped with such warning signs as are specified in item E5.
E8. If it is necessary to open an electric fence at places that are not accessible to the general public, parts that can be touched must be made of insulating material or be appropriately insulated from the fence.
E9. Fencing wire and lead-out feeds must not be attached to posts used for low or high-tension overhead transmission lines, or to telephone or telegraph wires. Electric fence apparatus connected to the mains may be attached to posts for low-tension lines provided permission has been obtained from the appropriate electricity utility, company or supervising authority.
E10. If an electric fence must be installed close to an overhead power line, the vertical separation between any fence wire or lead-out feed and the ground surface must not exceed two m. This distance applies to all points situated within the projection at right-angles of the outermost of the power lines onto the ground surface and a distance of two m outside thereof for power lines with a nominal working voltage not exceeding 1 kV, and a distance of 15 m outside thereof for power lines with a nominal working voltage exceeding 1 kV. Crossing overhead power lines must be avoided whenever possible. If such a crossing cannot be avoided, it must be made below the power line and at as close to a right-angle to it as possible. The separation stated above must be applied. If crossing overhead power lines cannot be avoided, the appropriate electricity utility, company or authority must be notified.
E11. Where fencing wires or lead-out feeds are installed close to overhead communication lines, the separation between any of the fence wires or lead-out feeds and these lines must be at least two m.
E12. Inside buildings, special insulation between the feeds and parts of the building connected to earth is required for lead-out feeds that work at a voltage exceeding 1 kV. This insulation may be achieved by having sufficient separation or using high-tension cables.
E13. If it is necessary to bury the lead-out feeds, a high contact resistance between the live feed and the surrounding ground must be ensured, for example by using a high-tension cable or a protective pipe made of insulating material. The effect of cattle hooves and tractor wheels sinking in must also be taken into consideration.
E14. If the earth lead of an electric fence is installed close to a building, the separation between this earth lead and the mains electricity earth protection and neutral connection must be at least 10 m. The electrode for the electric fence earth lead should preferably be installed in a location with damp earth to ensure a good contact. The electrode, unless being used with low-power battery- powered fences, must penetrate at least 0.5 m into the ground.
E15. When installing electric fencing wires and lead-out feeds, joints with metal wires of galvanically/metallically different materials must be avoided because this causes corrosion, which eventually leads to contact faults, particularly when the joint is subjected to damp. Measures must be taken to prevent interruptions at the joint.