Electric fencing effectively deters deer from gardens and fields by providing a memorable, yet harmless, shock. The power of this psychological barrier is measured in Joules, the unit of energy delivered by the fence charger. A Joule measures the energy output of the charger, which is the force behind the electric pulse. Deer require a relatively high-energy shock due to their thick hide and tendency to push through weak barriers, making a proper Joule rating a primary concern.
Understanding the Function of Joules
Electric fence charger ratings are listed as Stored Joules and Output Joules. Stored Joules represent the total energy held within the charger’s capacitor before release. This internal energy is not entirely transferred to the fence line due to inefficiencies in the charger’s components.
The conversion process, primarily involving the transformer, usually operates at 60 to 75 percent efficiency. This means a significant portion of the stored energy is lost as heat during the pulse creation.
The Output Joule rating is the only number that matters for deer deterrence. It represents the actual amount of energy delivered to the fence wire. This delivered energy creates the psychological barrier, training the deer to associate the area with an unpleasant experience. Always base purchasing decisions on Output Joules to ensure the animal receives the full deterrent force.
Determining Effective Joule Output for Deer
Deer are large, wild animals with insulating fur and thick hides, requiring a stronger shock than smaller livestock. The electrical pulse must be powerful enough to overcome this natural resistance and create a lasting negative association. Experts recommend the fence line maintain a voltage of at least 4,000 to 5,000 volts for reliable deer exclusion.
To sustain this necessary voltage over the entire perimeter, the energizer must have a sufficient Joule rating. For typical multi-strand deer fences, a minimum effective output of 0.7 to 1.5 Joules per mile is suggested. Professionals often recommend a minimum of 1.0 Output Joule per mile to ensure effectiveness even under less-than-ideal conditions.
Using a lower-rated charger risks an insufficient shock that deer may ignore or quickly forget. The goal is to deliver a distinct, high-energy pulse that strongly discourages further investigation. A more powerful energizer provides the necessary reserve capacity to overcome resistance factors, ensuring the psychological barrier remains intact.
Practical Factors Influencing Charger Selection
The ideal Joule output must be increased to compensate for environmental factors that drain power from the system. The total length of the fence line is a significant variable, measured by the number of wires multiplied by the fence perimeter. A multi-strand fence has a much higher wire load than a single-strand setup, requiring a proportionally more powerful energizer.
Vegetation load, such as weeds touching the bottom wire, creates a path for electricity to flow into the ground, known as a “short.” This contact significantly drains the Joules intended for the animal, reducing the effective shock strength. In areas with poor weed control, select a charger rated for significantly more Joules than the minimum requirement to maintain deterrent power.
The grounding system directly affects the delivery of Output Joules to the deer. The electrical circuit is only completed when the animal touches the fence and the electricity flows through the deer into the ground. A poor ground connection prevents the full force of the Joules from being delivered.
A proper ground connection often requires multiple six-foot-long galvanized ground rods driven deep into the soil and spaced six feet apart. More powerful chargers necessitate a larger, more robust grounding system to operate correctly.
Designing the Physical Deer Fence Setup
While the Joule output determines the shock strength, the physical design dictates whether the deer encounters the fence effectively. A common and highly effective setup involves a vertical high-tensile design using seven to nine strands of wire. These wires should be attached to posts standing approximately 70 to 72 inches above the ground, spaced closely enough to prevent the deer from stepping through without contact.
The strategic placement of the wires is critical. The lowest strands should be near the deer’s nose level, and the top wire acts as a visual deterrent to jumping. Another successful strategy is using offset wires or a double-perimeter fence, which creates a three-dimensional effect.
This design confuses the deer’s depth perception, making it difficult to judge height and distance. This encourages them to investigate with their nose rather than attempt a jump.
To ensure the deer makes contact with its sensitive nose, baiting the fence is a highly recommended technique. Small pieces of aluminum foil or tabs smeared with an attractant like peanut butter or molasses can be clipped to the hot wires. The deer is drawn to the smell, touches the bait, receives a distinct shock, and quickly forms a lasting aversion to the fence.