Electric Fence Anatomy

Let us first look at what an electric fence is.

An energizer generates high voltage impulses between its two output terminals by means of wires (different types to choose from).  The impulse is very brief and is repeated every 1 to 2 seconds. The fence design is intended to connect the animal to these two output terminals through these fencing wires. When the electrical impulse passes through a muscle in the animal it stimulates the muscle to contract. If you have not felt an electric fence before, the best description of the feel is like leg cramp but lasting for just a moment. By necessity it is very unpleasant so that it provides an effective deterrent when the animal next encounters the fence. The animal remembers the unpleasant experience and avoids touching the wires again. It is not injury or damage that produces the discomfort but rather the induced muscle contraction that is unpleasant.

The voltage in an energizer could be as high as 9500 volts which should be able to spark nearly 5mm (0.2″). Importantly, if the electrical impulse does not spark across this gap to the animal’s skin then the animal does not feel anything. Therefore, a higher fence voltage can mean increased reliability or effectiveness for well insulated animals.

It is also important to realize that more voltage does not always mean more discomfort. Perhaps you have experienced a spark from common static electricity? Did you know that such sparks can have voltages as high as 30,000 volts! Yet the sensation is generally just a slight pinprick feel. What is happening here? The nerves on the skin are being stimulated as the electrical discharge dissipates over the surface of the skin. This feels a little unpleasant but nothing like a properly induced muscle contraction from an electric fence. To induce a muscle contraction, you must have a voltage difference across the ends of the muscle. In other words, the electrical impulse must go through the animal. It also must go through the animal in such a way that stimulates many muscles to make the overall “feel” unpleasant enough.

How can one enhance the muscle contraction so that it provides an effective deterrent? Firstly, the electric fence energizer must be able to generate sufficient electrical energy (energy is measured in joules). Most electric fence energizers will do this. However, this energy must be delivered to the animal with minimal loss between the energizer and the animal.

In general, you will need these basic parts to build an electric fence.

• 1 – Fence energizer
• 2 – Earth stakes
• 3 – Fence wire or tape
• 4 – Insulators
• 5 – End strainers
• 6 – Fence warning signs
• 7 – Connection bolts
• 8 – Fence posts
• Fence energizers

A separate article covers this. Please enquire at the office.

• Earth stake

Electric fences work on the principle of simple electronics. For a good flow of live positive energy there needs to be good path to the negative earth. In standard electric fencing this is achieved in two ways.

1. Through the ground with electrical flow returning to an earth stake.
2. In poor soil conditions a return through an earth wire.

Both methods can be used in conjunction for better efficiency. Electric fencing is only as good as the earthing system.

 

• Fence wire or tape

Poly wires and poly tapes are primarily used in electric fences for their ability to improve the presence of an electric fence. It iscdddw a well proven fact that all animals including humans will recall (after varying amounts of exposure) that the higher visibility of the wire basically means “stay away”.

So, when looking at hot wire and hot tape products the best thing to look for is the ohms or resistance values of the products. This will give you a good indication ofdhow far a fence your product will be good for.

 

• Insulators

Be careful what you buy. Sunlight deteriorates plastic. So, buy good-quality, long-lasting insulators. Usually black ones are treated to resist degradation by ultraviolet light. Poor quality insulators turn white or clear after a few years in direct sunlight. When using plastic tubing as an insulator, do not staple it too tight. I once spent several hours trying to find a short in a gate. Finally, I discovered a staple had damaged the tubing next to a ground wire, causing a hidden short.

 

• End strainers

Premium heavy-duty end strain insulators are used for tensioning the ends and corners of your fence lines. Electric fencing galvanised wires should be strained to around 90 kg (200 lb) High tensile galvanised wire is best as it will not stretch like soft wire and short out. Ratchet strainers are ideal for short wire strains. For poly wire or poly tape fences it is still recommended to use end-strainers for longer runs so you do not put much strain on your standard insulators.

 

• Fence warning signs

When an electric fence is installed where it might reasonably be expected to be touched by the public, warning signs must be attached. The warning sign must be at least 200 x 100 mm in size and should be affixed to the fence at intervals not exceeding 90 meters. The sign should also display the words ELECTRIC FENCE or show the symbol depicted. Any lettering should be indelible, at least 25 mm high and it is recommended that the colour of the sign be yellow with black inscription. In areas prone to bush fires, power the fence line from the 1/2 voltage terminal or turn the energizer off on days of extreme fire danger. Do not connect an energizer simultaneously to a fence or to any other device such as a Cattle Trainer or Poultry Trainer because if lightning strikes your fence it will be conducted to all other devices. Young children should always be supervised by a responsible adult when near electric fencing. If in doubt check the regulations with your local authority.

 

• Connection bolts

Nemtek line clamp U bolts are used to join and electrically connect cables, wires, and poly ropes. The line clamp ensures that a good electrical connection is maintained between the joints so that the electric fence functions correctly.

 

• Fence posts

Electric fence posts come in numerous styles. Most fixed installations would use steel posts, timber posts or fibreglass posts.

Generally, for strip grazing and temporary electric fencing tred-in posts will be used.

Beware of overhead power lines