All fences discussed on these pages are variations on the same theme-enclosures of wires, carrying a high voltage, low amperage charge, delivered in short pulses. They are designed to cause pain or fear in an animal, but not to cause injury. Electric fences have been used for many years on farms and ranches to contain livestock. What works to keep cattle and horse in, also works to keep bears out!

Electric fences have three main parts. When used properly all three components create an open circuit, which closes when touched by a bear. This is similar to a lighting circuit in your home: the circuit remains open until you turn on the switch, which closes the circuit, and the light bulb comes on.

1. An electrical device called a charger or energizer pushes and regulates power through the wires of the fence. Chargers that plug into household current (110 Volts Alternating Current--AC) also convert this current to voltage in direct current (DC). These devices, weighing only a pound or two, have been used for many years on farms and ranches to contain livestock. What works to keep cattle and horse in, also works to keep bears out!

2. The wires of the fence carry the electrical charge. This is the "hot" part of system. When wires are touched, the bear is shocked. These wires are nothing more than uninsulated electrical wires set on posts to exclude a bear from a possible food source.

3. The grounding rod is usually a 4 ft. by 5/8th in. rod of metal driven into the ground. The rod attracts the electrical current after it passes through the bear. The power is then returned to the energizer through a wire between the energizer and the grounding rod. In order to be effective as a deterrent an electric fence must be properly grounded.

Uses of Electric Fences

Electric fences have been used successfully to deter bears around the following settings:

• camps           
• beehives        
• remote cabins and lodges      
• compost piles
• fish camps     
• fish cleaning sites       
• canneries       
• airplanes       
• garbage containers    
• freezers         
• rafts and boats          
• incinerators   
• butchered game         
• animal feed    
• garbage dumpsters    
• municipal landfills       

Charger or Energizers for Portable Fences
The charger is the most important and expensive part of an electrical fence. For an electric fence that you can put up and take down relatively easily, you will need a charger with the following qualities:

Low impedance chargers are recommended for all electrical fencing installations where the intent is to deter bears. These chargers are specifically designed to overcome loads-such as grass or branches that may inadvertently come in contact with and draw current from the fence. When selecting a charger specify a "low impedance" model.

Fence chargers should deliver between 5,000 and 7,000 volts. While the exact amount of power needed to deter bears has not been scientifically determined, it is the best estimate of wildlife professionals that these numbers are sufficient.

Joule ratings between .025 and 0.70 have proven effective for deterring bears. Electrical engineers determine power amounts in a measurement known as joules. Different energizers produce different joule ratings. It is suggested that when purchasing an energizer for a portable fence that it have a joule rating of between .025 and 0.70. Exactly what you need depends on the length of your fence, the number of wires used, and the severity of conditions. Be sure to describe your needs to your fence vendor who will help you with your design. Vendors are listed in the Resources section.

Power Sources for Energizers for Portable Fences
Your fence location will help determine the best power source for you. The best choice for a given situation is dependent on such factors as where you will place your fence, battery charging facilities, and weight.

It is easiest if you can plug into an outlet that connects to a village, town or suburban power supply. Chargers may be plugged into 110 volt AC (household) current.

Away from power supplies, 12 or 6-volt DC batteries are an excellent choice. These "wet cell" batteries can be charged with boat and car engines, portable generators, or solar panels.

9-volt dry cell batteries are an excellent choice for remote situations and for people who choose not to purchase a solar panel charger. They are lightweight, long lasting, and relatively cheap. They can be purchased with 150 amp hour ratings.
"D" cell flashlight batteries are useful when size and weight are an issue. Not as long lasting as dry cells

Wire for Portable Fences
The wires of the fence carry the electrical charge. There are two choices for portable electric fencing: polywire and electro-plastic netting. Other fencing wire made of steel or aluminum is adequate, it's just not as easy to use or transport
Stranded polywire consisting of at least six strands of stainless steel wire woven into a thin polyethylene rope is recommended. It has no "memory", is lightweight and easy to roll and unroll. The top strand of a polywire fence should be 1/2 inch polytape wire. If desired, polytape wire can be used for all the strands. Polytape wire has the advantage of being highly visible to both people and bears. However, a fence entirely of polytape needs to be firmly anchored in windy areas, and will attract frost and ice during freezing conditions.

Lightweight aircraft cable has also been used in portable fences that can then be rolled up and carried around as a unit. This type of conductor does not degrade in sunlight or crack in cold temperatures, and has no "memory."
We recommend a minimum of 3 strands of wire for portable fences, with the lowest wire at 10-12 inches and the upper wire at about 40 inches above the soil.

Electro-plastic netting has effectively deterred bears at fish weirs and hunting camps on Kodiak Island. It's cheap, lightweight and easy to set up.

Connecting Wires for Portable Fences
You will also need short lengths of 12 to 14-gauge copper electrical wire to connect the energizer and the fence, and the grounding rod and the fence. For portable fences some people prefer alligator clips as connectors to the energizer. A standard commercial ground rod clamp is often used to connect the grounding rod to the fence.

Grounding Rods for Portable Fences
Dry soils are less conductive to the flow of electric current. Therefore you may need larger and/or multiple grounding rods if your soil is very well draining. Your fence vendor can help you to choose how many rods you will need and the most appropriate size and material, for the type of soil around your fence. A single 4 ft. by 5/8 in. copper rod driven 2 or 3 feet into the ground is adequate in most soils. An electric fence voltage tester will help you determine if your ground is adequate.

Fence Posts for Portable Fences
Non-conductive plastic posts are a good choice for portable fences. Fence posts may be made of any material but wires must be insulated from touching the posts so that the electricity is not carried into the ground by the post. Many different commercial insulators are available and your vendor may have suggestions.

Fence posts may be optional in brushy or forested areas. Some people have had good success with suspending fence wires with "zip strips" (plastic wire holders) from convenient branches.

Gates for Portable Fences
Essentially a gate is a place where a person can interrupt the fence circuit and make a place so they can pass through without disrupting the wires. Gates generally need an extra post or two. The gate needs to be made of wire and insulated, and hooked up to the other wires so it is "hot." You may want to get insulated gate handles.

Voltage Meters for Portable Fences
It is important that your fence have 5,000 to 7,000 volts at all points along the wires. For this reason we suggest you purchase a voltage meter specifically designed to test electric fences. Such units should also indicate that your fence is properly grounded. These meters can be purchased from one of the vendors listed.

Electric fences are unlikely to harm people, pets or bears because the current or amperage is very low and is not likely to cause injury. However the voltage is very high, for this reason energizers send power through the fence wires in pulses, about once every second. Because the current isn't continuous, the animal or human that comes in contact with the wire has a chance to break free of the fence-feeling only a quick nasty jolt.

The Alaska Department of Fish and Game strongly recommends that you do the following to make your fence as safe as possible

• To be certain you are purchasing a charger that will not harm people, bears, or pets look for a UL-approved label that meets federal safety standards.
• Avoid "weed burner" chargers. They have longer electrical pulses than the low impedance models, being designed to burn off vegetation that comes in contact with the fence. These units present a fire danger.
• Place appropriate warning signs on the fence.
• Use highly visible polytape if you expect visitors to your fence site.
• Caution children about touching the fence, using the gate, and operation of the energizer.
• Do not set fences up in streams, lakes, or standing water. Water conducts electricity. Animals or humans that stand in water and touch the fence could receive multiple shocks that may cause injury.
• Consider using electro plastic wire mesh when possible, or when you think there is a possibility young children may play in the vicinity of the fence. Wire mesh is highly visible and it discourages children and small animals from entering between strands of wire.