Abstract:
An electric fence is disclosed for keeping selected small animals out of an enclosed area. The electric fence has an electrically conductive screen, a plurality of support members for supporting the screen, at least one electrically conductive element positioned adjacent to the screen on a side of the screen opposite the enclosed area, the electrically conductive element mounted to the fence by a plurality of mounting elements, the electrically conductive element being operably couplable to an electric charge generator, and the screen being electrically grounded. The electric fence may be mounted adjacent to a perimeter fence by a distance greater than the distance the selected animal can jump.

Description:
FIELD OF THE INVENTION 
     The present invention relates to electrified fences for keeping squirrels, rabbits, and other ground dwelling animals out of enclosed areas. 
     BACKGROUND OF THE INVENTION 
     Certain facilities, such as transformer substations, pose a potential hazard to both the public and wildlife. Occasionally, wild animals, such as squirrels or raccoons, may enter a transformer substation and short circuit a power line causing an outage. Chain link fences have been used to isolate the public, and to some extent, wildlife from distribution stations. Traditional chain link fences usually consist of a wire chain link screen or screen suspended between a plurality of suspension posts. Since the chain link screens are heavy and must be tensioned to maintain their structure, the supporting posts must be anchored to the ground, often by concrete backfills. Chain link fences have not proven effective in preventing the entry of squirrels and other small animals from transformer substations. Essentially small animals, particularly squirrels, are able to climb over chain link fences. 
     Occasionally, electrified fences have been used to keep certain animals, usually vermin, out of hazardous areas. These electric fences generally consist of a bare electrically conductive element, such as a wire or a metal bar, suspended on poles. The electric element is electrically coupled to a charging device. Occasionally, an electrified fence may have more than one conductive wire strung between the poles. To keep the electrified elements taut, tension must be applied; thus requiring the supporting poles to be anchored to the ground. The costs associated with building electrified fences with anchored support poles is relatively high since the anchoring of supporting posts is labour intensive. 
     Electrified fences have proven to be effective in keeping out larger animals, such as dogs or wolves, from enclosed areas; however, smaller animals such as squirrels, are often small enough to avoid the electrically charged wires of electric fences. Occasionally, these small animals are quick enough to pass through the wires between shock pulses (from the fence energizer) without receiving a shock. At other times, these small animals avoid the electrified elements of the fence by burrowing under the fence. As a result, the use of electrified fences has thus far not been effective in deterring squirrels and other small animals from entering certain enclosed locations such as transformer stations and distribution stations. There is a need for an effective and low cost fence which effectively prevents small animals, particularly squirrels, from entering enclosed areas such as electrical distribution stations. 
     SUMMARY OF THE INVENTION 
     The present invention is a system for keeping selected small animals out of an enclosed area, the system having a perimeter fence and an internal electric fence having an electrically conducting element. The internal electric fence is mounted parallel to the perimeter fence at a distance greater than the distance the selected animals are capable of jumping. 
     The present invention is also directed at an electric fence for keeping selected animals out of an enclosed area. The electric fence is made from an electrically conductive grounded screen supported by a plurality of support members. The screen is dimensioned to prevent the selected animal from penetrating the screen. At least one electrically conductive element is mounted to the electric fence adjacent to the screen and opposite to the enclosed area. 
     The present invention is also directed at an electric fence for keeping selected small animals out of an enclosed area, the fence having a grounded electrically conductive screen supported by a plurality of support elements. A portion of the screen is angled away from the enclosed area such that the selected animal will hang from the screen while attempting to climb over the screen. An electrically conductive element is mounted to the electric fence opposite the enclosed area and adjacent to the portion of the screen. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     Further features and advantages of the method and device embodying the present invention will now be described and made clearer from the ensuing description, reference being made to the accompanying drawings, in which: 
     FIG. 1 is a side view of the present invention; 
     FIG. 2 is a perspective view of the present invention; 
     FIG. 3 is a side view of an insulated support member of the present invention; 
     FIG. 4 is a top view of an insulated support member of the present invention; 
     FIG. 5 is a perspective view of a portion of the present invention showing an alternate mounting configuration; 
     FIG. 6 is a perspective view of a portion of the present invention showing another alternate mounting configuration, and 
     FIG. 7 is a side view of a top portion of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring firstly to FIGS. 1 and 2, the electric fence constructed according to the present invention, shown generally as  10 , comprises a fence  12  mounted to an electrified fence  18 . Fence  12  may comprise a chain link fence  12  having wire screen  16  supported between poles  14 . Poles  14  are anchored to ground by either concrete or some other anchoring system. Electrified fence  18  comprises support elements  20 , electrified wires  30  and screen  28 . Support elements  20  are preferably poles. Electrified fence  18  is mounted to chain link fence  12  by mounting arms  22 . Mounting arms  22  each have first end  32  adapted to securely and rigidly mount to poles  14 , and a second end  34  adapted to securely and rigidly mount to poles (support elements)  20 . Mounting arms  22  may be formed from a variety of materials such as metal or plastic tubes. First end  32  may be mounted to pole  14  by bracket  35 , and end  34  may be mounted to poles  20  by bracket  37 . To prevent small animals from jumping from fence  12  over fence  18 , the distance between fence  12  and  18  is chosen carefully. Certain small animals, such as raccoons, are not capable of jumping long distances, while other animals, such as squirrels, have been known to jump as far as five feet. Therefore, if fence  18  is more than five feet from fence  12 , squirrels, or other small animals, jumping from fence  12  will land short of fence  18 . To maintain this selected distance between fences  12  and  18 , mounting arms  22  are at least 5 feet long. 
     Poles  20  are securely mounted to fence  12  by mounting arms  22 , thereby eliminating the need to anchor poles  20  to the ground. This feature reduces the time necessary to construct electric fence  18  and eliminates the risk of cutting buried power lines, communications cables, or pipes. Preferably, poles  20  are made of an electrically insulating material such as plastic or wood. Ideally, poles  20  comprise elongated plastic “T-beams”. Alternatively, poles  20  may comprise metal pipes, metal beams or even wooden poles. 
     If attaching poles  20  to fence  12  is not practicable, or if no fence  12  is available, then poles  20  may be mounted directly to the ground by concrete backfilling or the like. Alternatively, as best seen in FIG. 5, poles  20  may be secured directly to anchored member  50  via mounting arms  22 . Anchored member  50  may comprise either short stakes driven into the ground or some other existing structure. As seen in FIG. 6, poles  20  may even be mounted to a wall  53  by mounting arms  22  and attachment bracket  52 . 
     Referring now to FIG. 7, poles  20  are provided with top portions  44  which are at an acute angle a from the main axis  45  of poles  20 . The angle at which top portion  44  extends from the rest of pole  20  is selected to ensure that any animal climbing electric fence  18  will have to hang from the top of the fence substantially upside down. Angle α should be less than 90°. Preferably, top portions  44  are at a 60° angle from the rest of pole  20  and preferably at a 60° angle from the vertical. Top portion  44  may be either integral with the rest of pole  20  or, alternatively, the top portion may comprise an angled member which is mountable to the end of the pole. 
     Screen  28  may be mounted to poles  20  via a variety of methods known in the art. Preferably, screen  28  is mounted to poles  20  by mounting brackets  24 . Mounting brackets  24  are preferably provided with fingers  26  which mount electric wires  30  to poles  20 . As best seen in FIGS. 3 and 4, mounting brackets  24  comprise an elongated member having a first section  38  adapted to mount to poles  20  and a projecting finger  26  configured to protrude away from first section  38 . Finger  26  further comprises a screen retaining portion  36 , adapted to retain screen  28  and a wire retaining portion  40 , adapted to hold electric wire  30 . Mounting bracket  24  is made from an electrically non-conductive material such as plastic. 
     Finger  26  is sufficiently long to ensure that electric wire  30  will be positioned a few inches from screen  28  when electric fence  18  is assembled. The distance separating wire  30  from screen  28  is important. If the distance is too small, then the chances of accidental shorting of wire  30  and screen  28  is high; however, if the distance is too great, then it is less likely that an animal climbing screen  28  will contact both the screen and the wire simultaneously. Preferably, the distance separating wire  30  and screen  28 , and thus the length of finger  26 , is selected to be between 1.5 to six (6) inches. It has been discovered that most small animals, including squirrels, are unlikely to pass through a gap within the range of 1.5 to six inches without contacting both screen  28  and wire  30  simultaneously. Wires  30  are attached to end  40  of fingers  26  of brackets  24 . It is also possible to mount wires  30  directly to screen  28  by a non-conductive member having one portion adapted to mount to the screen and another portion adapted to hold the wire. 
     Referring back to FIG. 2, screen  28  is made of electrically conductive material, such as galvanized steel. The screen size is sufficiently small to prevent small animals such as squirrels from passing through the screen. A portion of screen  28  may be buried into the ground a few inches to prevent small animals such as raccoons or rabbits from passing beneath the screen. Screen  28  is electrically grounded back to the electric fence energizer (not shown). Screen  28  is tensioned or stretched when it is attached to poles  20  to ensure that the screen does not sag or accidentally makes contact with electrified wires  30 . It has been discovered that 1“XI,” 16 gauge galvanized after welded (GAW) wire mesh makes a very effective screen against animals such as squirrels. 
     Electric wires  30  comprise wires made from an electrically conductive material such as copper, aluminum or galvanized steel. Wires  30  are tensioned to ensure that wires  30  do not accidentally touch screen  28 . In operation, electric wires  30  are electrified by the application of a high voltage electric charge. Suitable electric charge generators, or energizers as they are commonly referred to, are available in the marketplace. Since screen  28  is electrically grounded, any animal touching both the screen and an electric wire  30  at the same time, shall receive an electric shock. 
     At least one electric wire  30  is attached to electric fence  18 . Preferably, at least three separate electric wires  30  should be attached to poles  20 . A lower electric wire  31  extending parallel to electric fence  18  a few inches above the ground, an upper electric wire  33 , positioned on top portions  44  of poles  20 , and another electric wire  30 , positioned mid-way and parallel to wires  31  and  33 . Lower electric wire  31  is positioned approximately two to three inches above the ground and four to six inches from screen  28 ; permitting the wire to make electric contact with a small animal attempting to burrow under electric fence  18 . Upper electric wire  33 , is positioned towards the end of top portion  44 , opposite the enclosed area, such that any small animal attempting to climb over the electric fence shall make contact with the electrified wire. Other electric wires  30  may be mounted to poles  20  more or less mid-way between electric wires  31  and  33  to maximize the probability that a small animal attempting to climb electric fence  18  shall contact the wires. 
     It has been discovered that two or more electrified wires positioned on top portion  44  shall ensure that no small animal can climb over electric fence  18  without receiving an electric shock. Referring to FIG. 7, in addition to wire  33 , two additional wires  39  and  41  are attached to top portion  44 . Preferably wire  39  is positioned approximately 1.5 to 2.5 inches from screen  28  while wire  41  is positioned approximately three (3) to four (4) inches from screen  28 . Both wires  41  and  39  are further positioned about four (4) to five (5) inches from top edge  43  of screen  28 . Wire  33  is positioned about twelve (12) inches or so from top edge  43  of screen  28  and about three (3) to six (6) inches away from the screen. This combination of three electrified wires makes it nearly impossible for a squirrel or other animal to climb over screen  28  without touching one or more electrified wires. 
     To construct the electric fence, mounting arms  22  are first connected to poles  14  of chain link fence  12 . Brackets  35  may be used to rigidly mount arms  22  to poles  14 . Alternatively, arms  22  may be welded or brazed directly onto poles  14 . Once arms  22  are secured to poles  14 , poles  20  are then rigidly attached to arms  22  via brackets  34 . Poles  20  are oriented such that upper portion  44  faces towards chain link fence  12 . Since poles  20  are supported by arms  22 , poles  20  do not have to be anchored to the ground, thereby reducing the time and effort required to install electric fence  18 . Brackets  24  are then attached to poles  20  such that fingers  26  of brackets  24  point towards chain link fence  12 . Screen  28  is then attached to poles  20  by mounting the screen to brackets  24 . After screen  28  is properly installed and tensioned such that it is free of sags, electric wires  30  are attached to fingers  25  of brackets  24 . Electric wires  30  are then tensioned to ensure that they do not sag or touch any portion of screen  28 . After the entire perimeter fence is installed, electric wires  30  may be electrified. 
     In operation, any small animal, such as a squirrel, trying to gain entry past the electric fence will first have to scale chain link fence  12 . Since electric fence  18  is more than five feet from chain link fence  12 , the small animal will attempt to climb over the electric fence rather than jump over it. Since screen  28  is grounded and since electric wires  30  are electrically charged, the chances of the squirrel or other small animal climbing over electric fence  18  is minimal. Top portion  44  of poles  20 , being at an angle to the vertical, will force any small climbing animal to climb substantially upside down, thereby increasing the chances of contacting electric wire  33 . It has been observed that as soon as a squirrel or other small animal contacts an electrified wire while being grounded, the small animal falls from the electric fence and vacates the general area. 
     The invention having been so described, certain modifications and adaptations will be obvious to those skilled in the art. The invention includes all such modifications and adaptations which follow in the scope of the appended claims.