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The Milk House

Lessons learned in stray voltage

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Dairy basics - Herd Health
Written by Chuck Untiedt   

071111_voltage1The following information was written as a testimony to present to the Minnesota legislature earlier this year.

My name is Chuck Untiedt. I am from Lakefield, Minnesota. I am a lifelong dairy farmer, a stray voltage/current survivor, and I have survived the litigation wars.

In searching for help to correct the stray voltage/current condition on our dairy farm, I have learned the following:

1. It is the peak to peak current, and not the voltage, that affects the cows, which are ten times more sensitive than humans.

(Click here to see the image at right at full size.)

071111_voltage22. It is the resistance of the cow that determines the amount of current that a given voltage will push through her body. For example, if a cow has a resistance of 500 ohms*, 1 volt will push 2 mA** through her. If her resistance is 250 ohms, then 1 volt will push 4 mA through her. And if her resistance were 100 ohms, then 1 volt would push 10 mA through the cow.

  • If an animal has an open wound, a cut or something as common as a heel wart and the skin is broken, the resistance may be reduced by 55 percent or more. It all comes down to the math, and while the voltage is known to vary, so does the resistance of the cow.
  • The utility companies currently use a standard of 90 percent (of the herd being affected by stray voltage/current) before it is considered a concern. That number comes from the fact that the electrical industry uses 500 ohms to represent the resistance of a cow, when very often the animal’s resistance is much lower, exposing her to damaging current at voltages much lower than one volt. By using 500 ohms, you are at the top end of the resistance chart which means, arguably, you are affecting 90 percent of the animals before you consider it a concern.
  • We need to protect the most sensitive and the least resistive dairy animals — not just the most resistive and least sensitive. The sensitivity and the resistance both vary animal to animal, which is the same as in humans.

3. It is only the multi-grounded wye distribution that creates a stray voltage/current concern by design.

  • There are numerous ways to solve stray voltage/current conditions due to the mulit-grounded wye configuration. They include simple isolation from the primary neutral as allowed by NESC 97 D2, moving the source transformer or isolation transformers.
  • The problem can also be solved by transformation from the multi-grounded wye primary to different types of utility distributions that do not create stray/voltage by design.
  • Following are examples of the transformations that are available- a multi-grounded wye to:
    - an unigrounded wye
    - an ungrounded wye
    - a delta distribution
    - resonantly grounded
    - resistively grounded
    - a 5-wire distribution

4. Measurements to evaluate stray voltage/current:

  • We cannot expect yesterday’s meters to reveal all of today’s concerns and their sources. We need to measure the peak to peak values and their waveforms.
  • The use of modern digital switching technology in power distribution and control requires the use of modern, multi-channel recording voltage/current meters and high bandwidth oscilloscopes to fully and accurately identify stray voltage/current sources.

*Ohm is a unit of electrical resistance. Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference  across the two points, and inversely proportional to the resistance between them.

**mA = milliamps

For more information, contact Chuck Untiedt at This e-mail address is being protected from spambots. You need JavaScript enabled to view it or (507) 839-3739, or contact Don Johnson at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

 

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