Stray voltage, also known as stray current or stray electricity, is a reality. Many courts have addressed stray voltage--the concept is not new.
The concept of stray voltage is as follows:
All electricity leaving an electrical substation must return to that substation in order to complete a circuit. Unless that circuit is completed, electricity will not flow. The current leaves the substation on a high voltage line which eventually connects to some electrical 'appliance.' After exiting the 'appliance' that current must return to the substation.
The neutral-grounded network provides the returning current two choices. Either it can return via the neutral line, which accounts for the second wire on our electrical poles, or it can return through the ground. These two pathways comprise the grounded-neutral network. Electricity flows through the path of lowest resistance. If there exists more resistance in the neutral line than in the ground, the current will flow through the ground to return to the substation.
Neutral-to-earth voltage or stray voltage will occur when current moves from either the neutral line to the ground or from the ground to the neutral line. It uses a cow as a pathway if that animal happens to bridge the gap between the two. A cow's hooves provide an excellent contact to the earth while standing on wet concrete or mud, while at the same time the cow is contacting the grounded-neutral system consisting of items such as metal stanchions, stalls, feeders, milkers, and waterers. The current simply uses the cow as a pathway in its eventual return to the substation.
Very slight voltages can affect cattle. Evidence has shown anything greater than one volt can be catastrophic to a dairy farm.
A cow in contact with stray voltage experiences an electrical shock, and repeated exposure to these shocks cause a cow to develop severe behavioral and physiological problems, rendering the cow a much less-effective milk producer. Stray current can lead to health problems in cows such as mastitis, reproductive problems, and lower milk production. Dairy cattle are so sensitive that the normal low voltage existing on the neutral troubles them.
Stray voltage can come about due to a variety of failures on the part of an electric utility, including, but not limited to, undersized neutral lines, out-of-balance phases due to load imbalances over time, and degradation of the utility neutral due to stretching, corrosion, line breaks, splices, and loose connections.
When looking at issues of stray voltage on a dairy farm, it is important to draw a distinction between the utility primary system and the dairy farm secondary system. The utility is responsible for the primary system and farmer is responsible for the secondary system, but, a utility's negligent maintenance, operation, and inspection of its primary system can result in stray voltage found on the secondary system.