Stray voltage shouldn’t be a mystery


MADISON, Wis. – You may have read or heard confusing or conflicting opinions on the effects of “stray voltage” or other forms of electrical exposure on cows.

Studies by hundreds independent researchers in many countries give us a good understanding of the way electricity affects living organisms and the level of voltage and current exposure cause problems to cows.

The short answer is that animals will be affected if voltage and current exposure levels get high enough, however there is a threshold level below which no harm will occur.

Notable findings. Research summaries can be found at and Here are some of the notable findings.

* The first study of stray voltage published in New Zealand in 1962 concluded that three volts (60 hertz rms, or root mean squared) would be a likely minimum level for adverse effects on cows.

* A review by 15 scientists published by the USDA in 1991 concluded that exposure levels should kept below two to four volts (60 hertz rms) to prevent adverse responses.

* Research in the past 10 years has shown that high frequency events require much higher voltage and current exposure levels to elicit the same response as 60 hertz voltage and current.

* Minnesota commissioned a four-year, $4 million study by a team of eight national experts that concluded, “We have not found credible scientific evidence to verify the specific claim that currents in the earth or associated electrical parameters such as voltages, magnetic fields and electric fields are causes of poor health and milk production in dairy herds.”

* Michigan’s Attorney General investigated concerns about ‘ground currents’ created by utility grounding. An administrative law judge ruled that the complaint be dismissed because there was no evidence that problems resulted from grounding electrical distribution systems.

Wisconsin regulators established one volt in cow contact locations (two milliamps of 60 hertz current flowing through a cow) as the state standard. The research clearly supports this as a safe exposure limit.

The voltage and current exposure produced by ground currents are typically 100 to 1,000 times lower than this level.

What you can do. Stray voltage is not a mystery. We know how to measure it and we know how to reduce it.

If you have a concerned about electrical exposures on your farm request a measurement of cow exposure levels from your utility company.

Make sure your farm wiring and the utility wiring meets electrical safety codes and cow contact exposure guidelines.

Never compromise the safety of your farms electrical system in an attempt to reduce electrical exposure levels.

(The author is a professor of biological systems engineering at the University of Wisconsin-Madison.)


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