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Stray Voltage and Electrical Safety Problems I

Stray Voltage and Electrical Safety Problems Go Hand-in-Hand

John P. Chastain
Extension Agricultural Engineer


Stray voltage is a small voltage difference between two animal contact points. In dairy barns, this is often called a cow- contact point. A common example is a small voltage difference between the water cup and the floor of a dairy barn. When the animal touches both surfaces, completing the electrical circuit, a small current flows through its body. Elevated voltages across cow-contact points are called "stray" because they are not present under normal conditions. When voltages across cow-contact points are significant the production losses can be substantial. Fortunately, most dairy farms in Minnesota do not have problems with stray voltage. When stray voltage problems do occur the sources can be found and corrected as a result of a thorough investigation using the proper equipment.

Symptoms of stray voltage

Production losses are the result of animals altering their behavior because of the small shocks or tingles associated with high cow-contact voltages. These voltages are not large enough to harm the animal. If dangerous levels of voltage are present then a safety problem exists, and should be corrected immediately by a licensed electrician. Some of the changes in animal behavior are: (1) cows are excessively nervous during milking (dancing around in the stall); (2) cows are reluctant to enter the parlor or stall; (3) cows are reluctant to use waterers or to consume feed; and (4) poor milk letdown. Dairy producers should remember that these changes in animal behavior can also occur due to problems with milking equipment, changes in milking routine, spoilage of feed, or pollution of drinking water. Therefore, all potential sources of behavioral changes should be investigated. For more detailed information on the effects of stray voltage on dairy cows ask your county extension agent for a copy of the following extension bulletin:

Stray Voltage Problems with Dairy Cows (AG-BU-1359)
(How to order)

Causes of stray voltage

Sources of stray voltage can be from on-farm and off-farm sources. Off-farm sources of stray voltage can be related to primary neutral-to-earth voltages, and can be dealt with by your electric utility. Common on-farm sources of stray voltage on dairy farms are: worn insulation on wiring, loose wiring connections, improper use of equipment grounds, electrical shorts, unbalanced 120 volt loads, and improper installation of electric fences or cow trainers. All of these sources of stray voltage can be corrected. Finding and correcting sources of stray voltage requires a complete investigation by qualified professionals using the proper equipment.
Many of the on-farm sources of stray voltage are related to improper wiring practices for livestock buildings. Livestock buildings are dusty and damp as compared to residential buildings. Such an environment can cause electrical connections and insulation to deteriorate much faster than in other buildings. Therefore, the National Electric Code (Article 547) lists special requirements for wiring in livestock buildings. These requirements apply to all livestock barns, and milking centers. If these requirements are strictly followed then your building is "up to code" and the potential for stray voltage problems is greatly reduced. However, many dairy barns have not been wired according to the electric code, and the special requirements for livestock buildings have not been followed.
The special requirements for wiring of livestock buildings are explained in detail in the Farm Buildings Wiring Handbook (MWPS-28). The recommendations in this handbook are based on the 1990 National Electric Code. Detailed information on stray voltage, and how correction of farm wiring can help solve stray voltage problems are also given in this handbook. The handbook can be obtained from the University of Minnesota (see MidWest Plan Service).
Share this information with any licensed electrician who installs new equipment on your farm or alters any wiring. Be sure to specify that you want all work to be done in accordance with 547 of the National Electric Code. In addition, be sure that all electrical work is properly inspected as required by state law.

Improper grounding is a safety problem

Proper use of grounding wires on electrical equipment is required in all buildings. However, this is a common oversight on many farms. Improper grounding is not only a cause of stray voltage, but it is also a safety hazard. As long as all of the electrical equipment is in good condition then an improperly grounded system will work. However, if a motor or heating element fails then a person or an animal could receive a fatal shock due to improper grounding of the system. Such a condition is not a stray voltage problem (even though it can cause stray voltage), but is a safety problem. It should be corrected immediately. If a producer routinely feels shocks while operating electrical equipment or by touching metal in any type of livestock building then a grounding problem may exist.

What should be done if a stray voltage or safety problem is suspected?

If a stray voltage problem is suspected begin the problem solving process by taking all of the following actions -- do not delay.

  • Contact your electric utility and explain your concerns.
  • Your electric utility can provide a complete stray voltage investigation.
  • Obtain copies of the following educational materials from the sources previously indicated:
    Stray Voltage Problems with Dairy Cows (AG-BU-1359); and
    Farm Buildings Wiring Handbook (MWPS-28).
  • Have a licensed electrician inspect the wiring on your farm. Go over the information in the Farm Buildings Wiring Handbook with him or her. The handbook can be used as a guide for the special requirements of livestock buildings.
  • Make all wiring corrections that are needed. Remember that the safety concerns related to some wiring problems are more important than the stray voltage problem. You may solve a large portion or all of the stray voltage problem by correcting safety hazards.
  • Have your milking equipment dealer check out your milking system if it has not been done recently.
  • Contact your veterinarian to help you address any herd health concerns that may or may not be related to stray voltage.

On some farms it may be necessary for electric utility personnel to install an isolating device to reduce the stray voltage level. However, any electrical safety hazards should also be corrected. The complex electrical systems of dairy facilities sometimes need special attention to provide a safe and productive environment for the cows and the operators.

If you suspect that you have a grounding problem then have a licensed electrician inspect the wiring on your farm to determine if it meets all requirements for livestock buildings. Use the Farm Buildings Wiring Handbook (MWPS-28) as a guide. Make all necessary wiring corrections.

What measures can be taken to prevent stray voltage and safety problems in new livestock buildings and milking centers?

Make sure that all new livestock buildings and milking centers are wired according to the special requirements given in the National Electric Code (Article 547). Have the wiring properly inspected. Some insurance companies may require that all wiring meets code specifications for livestock buildings. Others may give a reduction in premiums if code requirements are met. In new milking parlors, installation of an equipotential plane and voltage ramp is highly recommended. An equipotential plane is created when the reinforcing steel in the concrete floor is electrically bonded to all metal equipment in the milking parlor. The complete system is grounded at the service entrance panel. A properly installed equipotential plane will maintain all floor surfaces and equipment in the parlor at the same voltage. As a result, no voltage difference can occur across cow-contact points. A properly installed equipotential plane will provide the greatest insurance against future stray voltage problems in milking parlors. The specifications for the proper installation of an equipotential plane and voltage ramp are given in the Farm Buildings Wiring Handbook.

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