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Thoughts on Stray Voltage

By Robert E. Graves

Agricultural, Biological, and Engineering Extension, Penn State University

Stray voltage has become a catchall term for anything that is or might be related to the affect of electricity on cow comfort and health on dairy farms. A lot of resources have been invested in learning about causes and possible affects of stray voltage; searching for stray voltage whether it was there or not; mitigating stray voltage; and litigating about stray voltage. Perhaps the biggest cost is the cost of the lost production and expenditure of effort and dollars chasing stray voltage problems instead of looking at other equally likely causes of the symptoms of concern.

At the recent Stray Voltage and Dairy Farms conference, co-sponsored by The Pennsylvania Department of Agriculture, in Camp Hill, Dr. J. R Roberts from Wisconsin stated, "Stray voltage presents a very appealing explanation for unresolved herd health problems. It is a real event. It is outside of the normal range of farm management concerns, and therefore, holds the potential for a guilt-free solution for the farmer. Furthermore, every dairy farmer is aware of testimonials claiming that stray voltage is an unrecognized cause of farm problems." He also reported that because most farm service professionals have inadequate understanding of stray voltage, they often add to the confusion. "Misinformation, misunderstanding and inadequate information are all hazardous to the success of any farm business." You may order the 400 page conference proceedings, NRAES-149, from the Natural Resource, Agriculture and Engineering Service at, 607-255-7654.

Based on this recent stray voltage conference and field experience, the following points seem pertinent:

  • Stray voltage is blamed for many problems that are caused by other management, health and equipment issues on dairy farms. This diverts attention and resources from getting the problem solved.
  • Stray voltage causes behavior change in dairy cattle. The avoidance behavior that results from animal contact voltages results in a variety of symptoms.
  • There are many places where voltages can be measured, but ultimately the current must run through the cow to affect the cow. Measurement of animal contact voltages must be a significant part of any stray voltage investigation and mitigation effort.
  • Stray voltage results from on-farm problems with electrical wiring and equipment and off-farm electrical distribution system problems.
  • Farm wiring is often the weakest link in on-farm stray voltage mitigation and prevention.
  • Lack of knowledge about stray voltage causes many on-farm professional advisors to add to the confusion that exists regarding this matter.
  • Equipotential planes and neutral reconnect devices can aid in control of neutral to earth voltage and animal contact voltage.

    Source: Penn State Dairy Digest, August, 2003

Stray Voltage Causes

The paths an electrical current takes to reach animals can be varied and complex. The causes and associated pathways can be either from on-farm or off-farm sources, or some combination of both.

Most of the problems stem from improper installation of electrical systems and milking systems. Improper maintenance can also be an issue.

Of course, problems can also originate from off-farm sources like utility system ground wires, high resistance utility neutral wires, and faulty transformers. In fact, it's not uncommon for utility lines to serve as pathways that simply allow a neighbor's electrical problem to show up on your farm.

Primary vs. Secondary Distribution Systems

Electrical systems-both on-farm systems and utility distribution systems-are grounded to the earth. From the grounding points, some current flows through the earth and a small voltage develops. This voltage is called neutral-to-earth voltage (NEV). When NEV is found at animal contact points, it is frequently called stray voltage.14

The NEV measured at any point on the system can come from two sources:

  • the primary system-the electric utility's distribution system
  • the secondary system-the farm's electric system

NEV can be due to either or both of these sources. If a farm has 10 service drops, then there are 10 potential secondary sources and one potential primary source.

However, research has shown that secondary NEV is the major source of stray voltage. 15

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