US Department of Agriculture, USDA Forest Service, Technology and Development Program Banner with Logos.
Images from various aspects of the T&D Program.
HomeAbout T&DT&D PubsT&D NewsProgram AreasHelpContact Us
 MTDC > MTDC Pubs > Specifications for Portable Electric Fence Systems as Potential Alternative Methods for Food Storage T&D Publications Header
Recreation Tech Tip
March 2007
2300 Recreation
0723-2305P-MTDC
Print this pub

Specifications for Portable Electric Fence Systems as Potential Alternative Methods for Food Storage

Dick Karsky, Project Leader
Kim Barber, Rocky Mountain Region
John Gookin, National Outdoor Leadership School
Gary Kees, Project Leader
Jim Claar, Northern Region

Since 1995, persons using any portion of the national forests in the Northern Continental Divide Grizzly Bear Ecosystem (NCDE) have been required to store food, garbage, and other attractants (such as horse feed) in a bear-resistant manner. A portable electric mesh fence system was evaluated to determine whether it was effective in keeping bears away from stored food (figure 1). The NCDE includes some wilderness and nonwilderness portions of the Flathead, Lewis and Clark, Lolo, and Helena National Forests south and west of Glacier National Park.

Two photos. Photo one is that of a portable electric mesh fence that is set up. The second photo is that of the equipment required for a portable electric mesh fence. Labeled in the photo are the diagonal corner braces, the storage bag, rolled fence and posts, energizer, grounding rod, LED warning light and the ground wire.
Figure 1—This portable electric mesh fence system is a potential alternative for storing food,
garbage, and other attractants in bear country.

Electric Fence Systems and Food Storage Orders

Portable electric mesh fence systems are being tested by MTDC and considered by land managers for approval as an acceptable means of meeting the requirements where food must be stored in a bear-resistant manner.

This document does not authorize the use of these fence systems to meet the various Forest Service food storage orders. Approval of any fence system for food storage must be provided by the land managers where this fence will be used.

These fence systems are intended to keep bears away from food, garbage, and other attract ants in the backcountry. They are not intended to protect campers from bears and have not been tested for such a use.

Several other portable fence systems have been tested that did not keep bears out. Energizers and fences that are not listed here must be evaluated by MTDC to determine whether they meet minimum specifications.

Similar storage requirements have been in place since 1990 in the Greater Yellowstone Grizzly Bear Ecosystem (GYE). The GYE includes some wilderness and nonwilderness portions of the Beaverhead-Deerlodge, Bridger-Teton, Custer, Gallatin, Targhee, and Shoshone National Forests. The area where these special orders apply is being expanded.

The National Outdoor Leadership School (NOLS) in Lander, WY, developed a portable electric mesh fence system as an alternative method of storing food in bear country. They have tested different configurations of the fence system over the past few years. The system has failed only a few times, usually because of human error or because animals accidentally ran into the fence at night and knocked it down. Flashing LED (light-emitting diode) lights were added to make the fence more visible.

The energizer weighs 1.8 pounds and the fence weighs 4 pounds. Without the braces, the kit weighs 7 pounds. With the five diagonal braces, the fence kit weighs 9 pounds, about as much as a heavy backpacking tent.

The Missoula Technology and Development Center (MTDC) and the Northern Region tested fence systems in 2003, 2004, and 2005 during the spring when bears were coming out of hibernation. A carcass was placed inside the fence as an attractant. Remote cameras monitored black bears and grizzly bears that visited the sites during the day and night.

Drawing of a grizzly bear.

Summary of Test Results

MTDC tested a number of battery-operated energizers in the lab to evaluate the voltage waveform and output energy of the different units (figure 2). Field testing determined which energizers kept bears out. As future energizers are evaluated, their voltage waveforms and output voltages can be compared to those of energizers that were successful in field testing.

MTDC tested the portable electric mesh fence system on the east slopes of the Rocky Mountains after the grizzlies had come out of hibernation in 2003 and 2004 near Choteau, MT, and in 2005 near East Glacier, MT. The fences were installed in areas heavily used by bears. Cow, horse, and deer carcasses were placed inside the fences to entice bears. Video cameras were installed to record bears actually making contact with the fence. Two test sites, each with a different fence configuration and/or energizer, were used each year.

In 2003, the portable electric mesh fence system was tested at two sites for 2 weeks. No failures were recorded during that time. Within 2 days after the fence system was removed, bears or other wildlife had eaten the carcasses or carried them off.

In 2004, the portable electric mesh fence system was again tested at two sites for 2 weeks. For these tests, an automatic automatic alarm system was installed that sent an e-mail message by satellite modem to MTDC offices in Missoula, MT, whenever a bear was detected in the area. One site had about 20 bear visits, some by the same bear, based on video imagery. The other site had 12 to 15 visits.

Bears got into the fence three times while we were evaluating different energizers. Two of the break-ins occurred when we were testing an energizer that proved to be too weak. Break-ins were no longer a problem after a 0.11-joule energizer was installed. The third break-in occurred when an early spring snowstorm buried the lower half of a fence, shorting it out.

In 2005, tests were conducted at East Glacier for 3 weeks. Bears visited nine times at one site and five times at the other. At one site, a bear that was digging contacted an energized wire. The bear raised up, pulling part of the fence out when it ran away. That bear was the only one that got inside an electric fence during 2005.

NOLS tested its portable electric mesh fence system for more than 3,000 user nights in 1995 in Wyoming, Utah, Idaho, and Alaska without any incidents. NOLS staff members think that the blinking LED lights are a big deterrent to bears.

Two graphs comparing the output electrical pulse of a Suregard Energizer and a Fi-Shock Energizer. Measured in microseconds the voltage is graphed between -5,000 and 8,000 volts. The oscillating pulse for the Suregard Energizer has a peak of high voltage and a steadily decreasing voltage over a longer period of time than the Fi-Schock Energizer which has a high voltage but a short duration.
Figure 2—Different energizers have different pulse shapes. Effectiveness appears to be a factor of
the total area (shaded) under the waveform curve. The "ringing" or oscillating pulse on the left
appears to be more effective than the pulse on the right. Also, a pulse with higher voltage and
amperage but a short duration is more effective and safer than a lower voltage with a
longer duration.

Electric Fence System Requirements

Table 1 summarizes the specifications of the fence system that has proven effective for food storage. As new components for electric fence systems are developed, they will require testing and approval.

Table 1—Summary of MTDC specifications for energizers and portable electric mesh fence systems.
Fence Height
Required: 33 inches
Recommended: 42 inches
Post length
Required: 42 inches
Recommended: 48 inches
Post construction
Required: Polyethylene with metal spike on bottom
Recommended: Fiberglass posts with metal spike
Strands of stainless steel wire per horizontal wire
Required: 3
Recommended: 9
A metal tab fastened to one of the horizontal strands of both the hot and ground wires is highly recommended as an attachment point for the energizer leads.
Number of horizontal wires
Required: 7
Recommended: 12 or more
Horizontal opening in mesh
Recommended: 6 inches or less
Maximum allowed: 12 inches
Length of ground rod (earth ground is mandatory)
Required: 1 foot
Recommended: 1 ½ feet
Energizer output
Required: 0.11 joules
Recommended: 0.2 joules
Tested peak output voltage (on every hot conductor, with no load other than the fence)
Required: 5,000 volts
Recommended: 7,000 volts
Minimum pulse duration (with a 10,000-ohm load applied)
Required: 0.05 milliseconds
Minimum shocks per minute
Required: 35
Recommended: 45
Distance between fence and items
Required: 1½ feet
Readable placard indicating fence is electrified
Required: 1
Maximum fence length
60 feet
LED lights
Required: 2
Recommended: 3

A ground wire return fence (with alternating hot—energized—and ground wires) must be used. Mesh with semirigid stays (figure 3a) is recommended to keep the mesh from drooping, which could allow the hot wires to short out against the ground wires below them (figure 3b).

Photo of a electric fence with vertical stays.
Figure 3a—Semirigid vertical stays (above) are preferred to flexible vertical
strands (below Figure 3b) because they prevent hot wires from sagging
and shorting out the fence.

Photo of a fence with flexible vertical strands.
Figure 3b—Unless this fence is kept tight, the flexible vertical
strands may allow hot wires to sag, shorting out the fence.

The recommended size for fence enclosures is 6 feet per side with five sides for the backpacker version (figure 4) and a maximum of 12 feet per side with five sides for the outfitter's version. The outfitter version must have diagonal braces on the corner posts. It can be created using two backpacker fences.

Drawing of an electrical fence enclosure that is measured six feet along the sides. In the center of the fence is a box labeled food that is 1 ½ feet away from the fence.
Figure 4—A recommended fence enclosure for
backpacker's food would have five 6-foot-long
sides. Food must be stored at least 1½ feet away
from the fence. Outfitters needing to protect
more food can combine two of these fences
to enclose an area with 12-foot-long sides.

Flashing LED lights (figure 5) are required on two sides of the fence to prevent persons, stock, and wild animals from running into the fence and knocking it over.

Make sure that the fence's bottom wire is near the ground, so that bears cannot crawl or reach under the fence without getting shocked.

If the fence is installed on wet snow, pack the snow down so it cannot short out the fence's bottom wire. A ground wire return fence with alternating ground and hot wires is effective even when the earth is too dry to be a good conductor. The grounded wires in the fence provide a direct electrical return path to the fence controller's ground terminal.

Because a bear must make good contact with two wires to get a shock, it may apply some force to the fence before the conductors work through the fur and contact its skin. This is why inside diagonal braces are recommended for the corner posts on the larger outfitter version (figure 6).

Photo of light-emitting diodes attached to electric mesh fence.
Figure 5—LEDs (light-emitting diodes) attached to
two sides of a portable electric mesh fence can
warn campers or animals before they touch or
run into the fence.

Photo of a bungee cord holding a brace against a post.
Figure 6—Bungee cords can be used to hold
diagonal braces against corner posts.

The ground rod provides an electrical circuit with the earth as the return path when the soil is moist. A bear will get shocked when it contacts any hot wire while standing on moist soil or when it touches a hot wire and a ground wire simultaneously.

Grass and weeds should be clipped or removed around the fence's perimeter so moist vegetation does not contact energized wires, even in windy conditions. Wet vegetation conducts some of the electric current to the ground and will decrease the shock delivered to a bear. Fences that contact wet vegetation are unlikely to produce the required 5,000 volts.

Check the fence with a fence tester that indicates voltage (Gallagher Model G50104 or equal). Place one lead on one of the energized wires and the other lead on a ground-wire. If the voltage reading is higher than 5,000 volts, the fence is working properly. If the voltage reading is lower than 5,000 volts, vegetation probably is shorting out the fence. Clear the obstructions and retest. Another possible cause of low fence voltage is a discharged battery.

Installing the Fence System

Choose a spot to install the fence system where the ground is fl at, no trees or brush hang over the fence, and where the fence does not block an established game trail. Unroll the fence and grab the posts, allowing the loops of mesh to droop between them (figure 7). To install the fence:

Photo of a man holding an electric fence system.
Figure 7—If the fence mesh has been gathered accordion style,
the fence will be easy to install.

  1. Hold the posts and allow the fence mesh to drop.

  2. Insert one of the end posts into the ground at your starting point.

  3. Insert each of the remaining posts into the ground to delineate the five sides of the fence (see figure 4).

  4. At the end, push the last post into the ground next to the first post.

  5. Reposition individual posts until you are satisfied with the fence's tension and shape.

  6. Attach the diagonal braces to the fence posts, if the braces are being used.

  7. Make sure that the energized hot wires are on the outside of the posts (figure 8).

  8. Place the energizer next to the posts just inside the fence where animals cannot damage it. Drive the ground rod near the energizer (figure 9).

  9. Clip electrical wires onto metal tabs crimped on the fence mesh near the end post (figure 10).

  10. Attach the energizer's green wire (ground, see figure 9) to the fence ground wire. Connect a separate green (ground) wire from the ground rod to the fence.

  11. Connect the white or red (hot) wire from the energizer to the proper metal (hot) tab on the fence mesh.
    CAUTION: If you do not connect the hot lead from the energizer to the proper metal (hot) tab on the fence and the ground lead to the proper metal (ground) tab on the fence, the energizer will not operate properly.

  12. Use adjustable bungee cords to attach the LED lights on two of the posts.

  13. If the soil is very dry, pour water over the ground rod to provide a good earth ground.

Photo of hot wires on the outside of a fence post.
Figure 8—Make sure that the hot wires (arrows)
are on the outside of the fence posts. Otherwise,
a bear could knock the post over without
getting shocked.

Photo of an electric fence labeling the diagonal brace, metal (ground) tab, green ground wire and the ground rod.
Figure 9—Connect the ends of the fence and attach the
energizer to the fence and the ground rod. The ground
rod should be at least 1 foot long. If the soil is dry,
pour water near the rod to ensure a good
electrical ground.

Photo of leads clipped from energizer to the hot wire labeling the metal (ground) tab.
Figure 10—Clip the leads from the energizer to the hot
wire (shown) and ground wires of the fence.

Using the Fence System
  1. After food has been placed in the middle of the enclosure, close the fence. With the energizer outside the fence, turn it on. After you are sure the energizer is operating properly, carefully slide the unit under the fence into the fenced area. The fence's bottom one or two wires are ground wires, so you should be able to do so without getting shocked. The energizer must be inside the fence to keep it out of the reach of animals.

  2. Use a fence tester (Gallagher Model G50104 or equal) to check the fence voltage. Place one lead on one of the energized wires and the other lead on a ground wire. If the voltage reading is higher than 5,000 volts, the fence is working properly. If the voltage reading is lower than 5,000 volts, food must be stored by another approved means, such as hanging it properly from a tree.
Removing the Fence System
  1. Turn the energizer off.

  2. Disconnect the energizer and electrical fence connections.

  3. Remove the LED lights.

  4. Remove the diagonal braces, if they were used.

  5. Pull each post from the ground as you walk down the line.

  6. Gather up the fence by collecting the posts with the loops of mesh drooped between them (see figure 6). Allow the mesh to fold into loops, accordion style, as you proceed.

  7. Lay the fence flat on the ground and roll the mesh around the posts.
Suppliers of Energizers and Electric Mesh Fences That Meet Specifications

Power Innovations (Models: Sureguard S4-Plus, S4, S10, and M-4)
110 Barton Rd.
Lismore, NSW2480, Australia
Phone: 61-2-6628-2000
Fax: 61-2-6628-2022
Web site: http://www.sureguard.com.au
Email: help@sureguard.com.au

Gallagher Power Fence (Models: B11, B75, and B80)
18940 Redland Rd.
San Antonio, TX 78270-8900
Phone: 800-531-5908
Web site: http://www.gallagher.com.au

Stafix (Models: B0.5 and AN90)
Web site: http://www.stafix.com/Default.asp?Country=United%20States

PEL (Models: 901B and 110B)
Web site: http://www.pel.co.nz/

Electric Mesh Fences That Meet Specifications

J.L. Williams Co. (Models: Electro-Web P-75 and P-89)
P.O. Box 209
Meridian, ID 83680
Phone: 800-843-3702
Email: freeinfo@safefence.com

Kencove Farm Fence, Inc. (Models: NSG, and NSG12X)
344 Kendall Rd.
Blairsville, PA 15717-8707
Phone: 800-536-2683
Email: fence@kencove.com
Web site: http://www.kencove.com

Premier 1 Supplies (Model: Electronet)
2031 300th St.
Washington, IA 52353
Phone: 800-346-7992
Email: info@premier1supplies.com
Web site: http://www.premier1supplies.com

Recommended Fence Improvements

The fence's current configuration uses alligator clips attached to metal tabs that allow improper electrical connections. A better alternative would use polarized connectors (figure 11), that would always connect hot to hot, and ground-to-ground.

Photo of polarized connectors.
Figure 11—Polarized connectors could prevent
improper electrical connections.

Maintenance Tips

Voltage

  • Clip grass, weeds, and branches around the fence's perimeter so moist vegetation will not contact hot wires, even in windy conditions. Retest the fence's voltage.

  • Clip the hot lead to the solid metal connector rather than a piece of plastic twine and ensure that the ground lead is connected to the ground clip on the fence. A separate wire should connect the ground clip to the ground rod.

  • Find a good ground by using the ground rod to probe for damp soil.

  • Clean the energizer's battery contacts with a pencil eraser.

  • Use dry silicone spray on the charger in humid areas. Silicone will reduce the possibility that moisture will allow the high voltage current to arc to the energizer's case.

  • During cold conditions, use new batteries and replace them more frequently than when it's warm. Solar energizers, such as the Sureguard S4-Plus, may not keep the batteries fully charged from November through February, when days are short and temperatures are low.

  • Make sure that the ground and hot leads are connected correctly or the fence will not operate properly.

Care

  • Care for the energizer the way you would care for a cell phone, radio, GPS receiver, or other electronic device.

  • Place the energizer in a dry, foam-padded case before transporting it.

  • Clean the battery contacts with a pencil eraser as needed.

  • Keep your energizer dry. If it falls in water, open the energizer's case and dry it in the sun or expose it to a breeze before turning it on.

Troubleshooting

  • Are the batteries holding a charge? Use new batteries to see whether they fix the problem.

  • Is anything corroded? If so, try cleaning the battery contacts with a pencil eraser.

  • Are the hot and ground lead wires connected properly?

  • Are the wires intact?

  • Is the energizer dry? If it looks wet, try opening the energizer's case and drying the energizer in the sun or exposing it to a breeze before turning it on.

  • Does the green (ground) wire go from the ground clip to the ground stake?

  • Does the red (hot) wire go from the energizer to the white (hot) wire tab on the fence?

  • Is anything inside the energizer obviously broken or disconnected?

  • Have you tried tinkering? If you do, remember that the first rule of intelligent tinkering is not to lose any parts.
Acknowledgments

The authors would like to thank:

  • NOLS staff members for developing this fence system and providing materials and data for the laboratory and field tests.

  • Mark Hinschberger, Shoshone National Forest, for his work with NOLS in developing the backpacker fence system.

  • Dan Carney, biologist for the Blackfeet Tribe, for field testing prototype fences and sharing his knowledge of bear behavior.

  • Mike Madel and Mike Maples of the Montana Department of Fish, Wildlife and Parks in Choteau, MT, for allowing us to test the prototype fence system on the east slopes of the Rocky Mountains and helping us monitor the test sites.

  • Brian Castaldi, MTDC, for helping install the camera monitoring system.
About the Authors

Dick Karsky has been program leader for forest health protection, GPS, and the air portion of the watershed, soil, and air program since the fall of 1999. Karsky has been a project leader at MTDC in the resource areas of GPS, range, cooperative forestry, engineering, fire, reforestation and nurseries, residues, recreation, and forest health protection. He received a bachelor's degree in agricultural engineering from North Dakota State University and a master's degree in agricultural engineering from the University of Minnesota. He worked for private industry before coming to the Missoula Technology and Development Center in 1977.

Kim Barber has been the grizzly bear and wolf biologist for the Rocky Mountain Region of the Forest Service since 1992. Barber, who is based in Cody, WY, represents the six National Forests in the Greater Yellowstone Area (GYA) on the Interagency Grizzly Bear Study Team, leads the Grizzly Bear Cumulative Effects Modeling Team for the GYA, and serves on various technical teams for the Interagency Grizzly Bear Committee. He has also worked for the Forest Service in Utah, Nevada, and Alaska. He received a bachelor's degree in zoology from Weber State College and a master's degree in wildlife management from Utah State University.

John Gookin is the curriculum and research manager and a senior instructor at NOLS in Lander, WY. He received a bachelor's degree in biology and environmental studies from Lake Forest College in Chicago, IL. He taught high school science and was a U.S. Marine before joining NOLS in 1981.

Gary Kees is a project leader specializing in reforestation and nurseries, facilities, recreation, and GPS projects at MTDC. He received his bachelor's degree in mechanical engineering from the University of Idaho. Before coming to MTDC in 2002, Kees worked for the Monsanto Co. in Soda Springs, ID, as a mechanical/structural engineer and project manager.

Jim Claar joined the Forest Service in 1989 and has helped establish standards for food storage and other techniques for living and recreating in bear country. He has been the leader for the Northern Region carnivore program since 1999. Jim also serves as the team leader for the national lynx biology team, team leader for the interagency wolverine biology team, and regional lead for interagency gray wolf coordination. He has a bachelor's degree in wildlife biology from the University of Montana and a master's degree in wildlife management from the University of Idaho.

Additional single copies of this publication may be ordered from:

USDA Forest Service
Missoula Technology and Development Center
5785 Hwy. 10 West
Missoula, MT 59808-9361
Phone: 406-329-3978
Fax: 406-329-3719
Email: wo_mtdc_pubs@fs.fed.us

Electronic copies of MTDC’s publications are available on the Internet at:

http://www.fs.fed.us/eng/pubs

Forest Service and Bureau of Land Management employees can search MTDC’s documents, CDs, DVDs, and videos on their internal computer networks at:

http://fsweb.mtdc.wo.fs.fed.us/search/

For additional information about [portable conveyors], contact MTDC:

Phone: 406-329-3900
Fax: 406-329-3719