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 Technology & Development Center |
| March 1999 | 2300 | 9923-2321-MTDC |
Dave Gasvoda, Project Leader
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 (Special Order No. F10014S95). The area includes wilderness and nonwilderness portions of the Flathead, Lewis and Clark, Lolo, and Helena National Forests south and west of Glacier National Park (see map).
Electric fence systems are an acceptable means of meeting the requirement for storage in a bear–resistant manner. Electric fence systems can be used alone or to supplement other forms of bear–resistant storage, such as using bear–resistant containers, or suspending attractants from a support.
It is the user's responsibility to operate the system in the field at the required levels. Forest Service employees will inspect electric fences when they are set up in the field.
Fence systems must meet the following minimum requirements:
Each conductor must have a tested minimum of 5000 volts. The voltage must appear at least 40 times a minute.
*Height above ground; distance between wires may vary from 6 to 10 inches.
The fence must be high enough that a bear cannot walk or jump over it. The wires must be close enough together so that a bear cannot get its head through without contacting the wires.
The top fence conductor may be high–visibility fence ribbon (Polytape) to decrease the chances of accidental human contact.
A ground wire return fence is effective when the earth is too dry to be a good conductor and make a good electrical connection to the bear’s feet. The grounded wires in the fence provide a direct electrical return path to the fence controller’s ground terminal. Because the bear must make good contact with two wires to get a shock, the bear may apply considerable force to the fence before the conductors work through the fur and contact its skin. This is why the ground wire return configuration requires strong fence wire and sturdy corner posts. Also, Polywire needs to be pulled tight to prevent sagging that could short hot conductors to ground conductors.
The ground rod provides an electrical circuit using the earth as the return path under wet conditions. A bear will get shocked when it contacts any hot conductor while standing on wet soil.
Grass and weeds should be cut short so most vegetation around the fence perimeter does not contact any hot wires, even in windy conditions. Wet vegetation conducts some of the electric current to ground and will decrease the shock delivered to a bear. Fences that contact wet vegetation are unlikely to produce the 5000 volts required by the inspection test.
Manufacturers refer to fence controllers as "energizers," "chargers," and "fencers." It is difficult to compare the controllers from different manufacturers because specifications have not been standardized. The controllers being marketed for pet control are not likely to be suitable.
Gallagher Model B50 (which has been superseded by Model B75) and Model B150 have been used successfully for bear fences by the Montana Department of Fish, Wildlife & Parks.
Other models stated by their manufacturers to meet the 6000 volt and 0.7 joule specifications are:
| Bear
Fence Models that Manufacturers Claim Meet the 6000 volt and 0.7 joule specifications |
|
|---|---|
| Fi-Shock | Model SS–7000 |
| Parmak | Model MAG.–12 SP |
| Red Snap’r | Model LIB–15 |
| Speed–Rite | Model SB 1000 Model SB 1500 Model SB 5000 |
Manufacturers whose literature does not specify stored energy in joules must specify in writing the models that meet the minimum stored energy requirement of 0.7 joules.
Very high energy controllers are not recommended because they are expensive, large, and heavy, especially when the battery requirements are considered. They can deliver a nasty or perhaps even fatal shock to humans who might accidentally contact the fence.
Solar–powered fence controllers are recommended for most installations. The battery life for most non–solar powered controllers depends on the capacity of the battery and the power used by the fence controller. Solar panels will usually eliminate the need to charge or replace batteries, allowing smaller, lighter batteries to be used.
A solar–powered unit should be located so it will be in direct sunlight most of the day.
Two types of suitable electric fence testers are available. The least expensive types use five to eight glow lamps that progressively light for increasing voltage. They can not be read in direct sunlight.
Digital volt meters are more expensive, but are considerably more accurate and are easy to read. Some digital meters are considerably better than others. Units that are polarity sensitive are not recommended. These require that the meter leads be reversed to obtain an accurate reading with some fence controllers. Therefore, the ground lead must be connected to the hot fence wire. This is awkward and greatly increases the chances of the operator being shocked.
The Gallagher Model G503 Digital Volt Meter is recommended for use by Forest Service personnel when they inspect the bear fences.
| Summary of Fence Specifications | |
|---|---|
| Minimum fence height | 4 feet |
| Minimum post length | 5 feet |
| Maximum spacing between posts | 8 feet |
Conductors must be:
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| Minimum distance between fence and items inside | 3 feet |
| Ground wire return fence must be used (alternating hot and ground wires) | |
| Minimum length ground rod (earth ground mandatory) | 2 feet |
| Minimum stored energy of the fence controller | 0.7 joules |
| Minimum tested peak output voltage on every conductor | 5000 volts |
| Minimum shocks per minute | 40 |
| Minimum number of wires | 7 |
| Distance between wires | 6 to 10 inches |
The author would like to acknowledge the contributions of Mike Madel, Bear Management Specialist for the Montana Department of Fish, Wildlife and Parks in Choteau, Montana. Mike’s work helped establish the requirements that must be met to successfully deter grizzly bears.
Additional single copies of this document may be ordered from:
The Forest Service, United States Department of Agriculture (USDA), has developed this information for the guidance of its employees, its contractors, and its cooperating Federal and State agencies and is not responsible for the interpretation or use of this information by anyone except its own employees. The use of trade, firm, or corporation names in this document is for the information and convenience of the reader and does not constitute an endorsement by the Department of any product or service to the exclusion of others that may be suitable. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382(TDD). USDA is an equal opportunity provider and employer.
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