Volts vs Joules

When determining the electrical needs of your fence system it is important to recognize the difference between volts and joules. A volt is a unit of measure assigned to the electrical potential or voltage across a conductor. However a joule is a unit of energy or work done, to move an electric charge through an electric potential. The following are mathematical understandings of volts and joules, which later will be put into layman’s terms according to choosing the correct energizer.

The difference between volts and joules can be simplified by remembering that joules are the energy used to create voltage on the fence line. Whereas, voltage is the speed at which the current is moving along the line. The diagram below is an excellent example of volts and joules.

    Joule = Truck

    Hill = Fence

    Speed = Voltage

    Weight = Ohms/Weed load/Resistance

When selecting a truck to haul livestock, you must first determine the heaviest load that the truck will need to pull. The truck must be capable of pulling the trailer and stock successfully. Choosing the appropriate energizer for your fence system is a very similar concept. Consider that the voltage is carried by the speed at which the charge travels through the fence line and joules will be created by the energizer according to the watts per second of output. In an electric fence system, a high voltage is important for making sure that an electrical charge can find its way through the hair on the animals it is intended to contain or exclude. The more or thicker the hair, the greater the voltage required. The higher the voltage, the greater the charged wire’s ability is to shock the animal that happens to touch the wire. The longer the fence line (mileage) and the heavier the weed load or resistance on the fence, the more output joules the energizer will need to maintain a volt range between 5,000 and 10,000 volts for good stock control.


Recommended Voltage

on Fence Line


5,000 Volts


5,000-10,000 Volts


5,000-10,000 Volts


5,000 Volts


5,000-10,0000 Volts


5,000-10,000 Volts


3,000 Volts


“It is always best to take the path of least resistance.” This is exactly what to keep in mind when building and choosing an energizer for your fence system. Resistance will decrease voltage on your fence line, because each energizer only has a specified amount of output joules (energy) to maintain the voltage along the conductor (fence line). When resistance begins to diminish output joules the voltage falls low enough that it becomes ineffective because it cannot bridge or arc across the insulation of the hair and hide of the animal. The following are common causes of resistance:

  • Weed Load
  • Induction- Stray voltage bridging to neutral wires, gates, diagonal braces wires, etc.
  • Bad Connections
  • Multiple Splices
  • Broken Insulators
  • Type of wire- Poli-wire, Tape, Ribbon, High Tensile, etc.
  • Rusty Wire

Generally rule of thumb is a minimum of 1 joule of output per mile of fence, to maintain a secure voltage. Kencove is willing to step outside the box and state, “This is not enough power once you do the math!” A mile is equal to 5,280 feet, which in turn is equal to the perimeter of 40 acres. Would you want a 1 joule unit to power your multi-strand 40 acre paddock? The easy answer is “NO”. Kencove would recommend at least a 6 joule unit with an open circuit voltage of 9,500 volts. Understand that if your fence line has numerous sources of voltage leakage, you will need to choose an energizer with a higher joule rating. The truth of the matter is that you can never have too much power. When training livestock having too little power is no different than having no power at all and the fence could actually causes harm to the animal.

Commonly energizer manufactures and dealers overestimate the amount of fence an energizer will securely power. In today’s world it is easy to fall for attractive ads and eye appealing packaging, so when purchasing an energizer look closely at the details.


Output Joules

Stored Joules

Open Circuit Voltage

500 Ohm Load



1.5 J

2.14 J

9,100 V

5,000 V


3 J

4.28 J

10,000 V

5,600 V


6 J

8.57 J

10,000 V

6,000 V

Many manufactures rate their energizers. A unit which is rated as a fifty-mile unit only means that it can essential power 50 miles of a weed free, well insulated, single strand wire. You will be disappointed if you select an energizer based on miles of fence line. Ultimately, the output joules of the energizer should be the selling point. If only stored joule information is available, you can estimate that output joules are about 70% of the joules stored within the units capacitors.

Remember, that the energizer is the heart of your fence system. It should be accurately sized according to what type of animals are being contained or excluded, the length of the fence line, and how long it could potential be in the future, as well as possible resistance on the fence. This is a basic description of the relationship between volts and joules, and the effectiveness of your electric fence.  Kencove hopes that through your comments and input the readers of this Blog will be able to have greater insight into the proper energizer for their fence.

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  1. mike
    Posted January 2, 2016 at 8:17 pm | Permalink

    I think i get the 1 joule per mile minimum, but I am looking at some solar chargers and all of them seem to be less than 1 joule yet claim they can do multiple miles? I see various products from .15 joule for 10 miles, .05 joules, .5 joule, but none in the 3-6 joule range of an AC. What gives, are you saying the solar products don’t work for any distance of consequence?

    • Lacy Weimer Lacy Weimer
      Posted January 4, 2016 at 9:33 am | Permalink

      Many manufactures rate energizers according to acreage or mileage, but keep in mind that rating is for picture perfect fence. Solar energizers are just as powerful as DC units. .15 joule will not keep a good voltage for 10 miles, especially if you are using any poly wire products or have a few connections. Solar energizer manufactures make small self contained units for small pets, gardens, small paddocks, and even beekeepers. If you are looking for a 3-6 joule range system you will need to purchase an AC or AC/DC fence charger, solar panel, solar charge controller, and deep cycle marine battery. These systems are very easy to setup and shock just as well as a DC unit. Check out these AC/DC energizers, charge controller and solar panels.

  2. Blake
    Posted May 23, 2015 at 12:50 pm | Permalink

    I have 600 ft of fence of 12.5 gauge HT. 3 strands are hot for a total of 1800 ft. Is a 1 joule output ac charger sufficient?

    • Lacy Weimer Lacy Weimer
      Posted May 27, 2015 at 2:48 pm | Permalink

      Yes one joule of out should work just fine.

      • Sam goodson
        Posted November 1, 2015 at 8:46 am | Permalink

        I got 15 acres tie fed in with horses and cows in !! How many mile charger do I need ??????

        • Lacy Weimer Lacy Weimer
          Posted November 4, 2015 at 12:26 pm | Permalink

          As long as fence is in great working condition and weed low is light a one joule charger will get the job done. Can always go one joule higher for safety!

  3. Jamie
    Posted September 28, 2014 at 9:58 am | Permalink

    I am trying to figure out the correct amount of joules that I will need for my pasture but I am still unclear. The perimeter of my pasture is 1 mile with three strands. So if I am correct I would consider it 3 miles which is 3 joules, right? Now a portion (about 1/3)of our pasture goes through a wooded area with weeds so we would need a higher joule rating to push through the weeds and keep the current strong, correct? I am confused though on how many more joules we will need to make this work correctly. How can I figure that out?

    • Lacy Weimer Lacy Weimer
      Posted September 30, 2014 at 8:48 am | Permalink

      A joule per mile is a minimum, so you want at least three joules for that amount of fence. Add an extra joule for every mile of weed load.
      I would recommend no smaller than a 4 joule unit for your fence line. There are very few 4 joule units so you many end up rounding to a 6 joule unit…stronger is always better!

  4. Lee Jones
    Posted September 18, 2014 at 9:43 am | Permalink

    I’m building a very small 8 feet x 6 feet enclosure to protect two beehives from bears.
    Will likely be using a mesh heavy gauge wire – openings in wire about 5×5. A gate along the 8 foot side – may add a second gate on the back 8 foot side for easy access. Additional wire to make connections to charger/ground.
    Given that the perimeter is so small – is 0.5 joule enough? or should I go 1.0 joule?
    Also concerned about harming other animals – deer, raccoon…

    • Lacy Weimer Lacy Weimer
      Posted September 26, 2014 at 6:59 am | Permalink

      A half joule (.5) unit is perfect. Most hives are kept behind a .5 joule unit, just be sure there are no shorts and that you have good connects. This will not harm any other animals.

  5. Mike Johnson
    Posted August 5, 2014 at 7:46 pm | Permalink

    I bought a thirty mile charger but only have a three acre spread. The fence is too hot for my wife to move the fence handle. Output is about 16K. Is there any way to make a fence weaker?

    • Lacy Weimer Lacy Weimer
      Posted August 7, 2014 at 9:05 am | Permalink

      I don’t think that your charger is too big. This is probably only about a 1.5 joule output unit, which is great for about 1.5 miles of fence. Take a closer look at the gate handle, the plastic is probably slightly cracked somewhere.
      Also check the quality of plastic that your gate handle is made from, the sun may have caused the plastic to be faulty. Please let me know of your findings.

  6. Ken Smith
    Posted April 20, 2014 at 10:19 am | Permalink

    Is it possible to buy an energizer that it too strong, hurting smaller animals such as chicks? We are looking for fencing to move small sheep and goats throughout a field, guarding from coyotes especially, but our chickens with their babies wander around the same area.

    • Lacy Weimer Kencove
      Posted April 29, 2014 at 7:33 am | Permalink

      Chicks should not be near your electric fence…they can be killed by the voltage.
      You should size your energizer to your fence. We generally recommend 1 joule of output per mile of fence.
      If you are using electric netting, we recommend .25 joule of output per net. However using a larger energizer will not harm goats and lambs. For maximum predator control keep 4,000-6,000 volts on your fence.

  7. Dan S
    Posted November 16, 2013 at 10:36 pm | Permalink

    Great useful information. Does more Joules mean that the current can power through problem areas such as snow on lines etc.?

    • Kencove kencove
      Posted November 19, 2013 at 9:14 am | Permalink

      Yes, as long as you purchase a larger joule charger than what is needed for the perimeter footage. This will help the voltage to push past the weed or snow load. The rule is one joule per perimeter mile of fence.

  8. Kencove kencove
    Posted May 25, 2013 at 12:15 pm | Permalink

    The most frequent solution is a short tube insulator (item code I50). But because your brace is already built, you could pull the diagonal wires together by wrapping with high-tensile wire or install a split bolt. Using coated wire for the diagonal would also solve this problem. Another way to avoid the hot wires touching is using insulator tubing with a Quik Brace. You can see that product & video here: http://www.kencove.com/fence/Quik+Braces_detail_HQBS12.php

  9. Ken Hess
    Posted May 25, 2013 at 10:24 am | Permalink

    After I installed my diagonal figure eight braces for my end posts, some of my hot wires are touching the brace wires. How can I keep them apart? Is there a product I should use or should I re-do my diagonal brace wires? Any help you can provide will be appreciated!


    • Steve Freeman
      Posted October 13, 2014 at 8:45 pm | Permalink

      We’ve found the Spiralator insulator to work very well when the hot wires touch the diagonal brace wires. You can add these after construction and we use them to replace old tube insulators that have cracked. We love this product.

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