Stray voltage is a small voltage that can be measured between two contact points. When these two points are connected together by an object, such as a person or an animal, a current will flow. The amount of current depends on the voltage and the circuit impedance, which includes the source, contact and body impedances. People and animals respond to the resulting current flow and not to the applied voltage.
Because stray voltage is normally related to very low voltage and current, it sometimes is not detectable and therefore not a problem. However, when people start to get shocked, it becomes more of a safety-related issue and if not corrected, has the potential to be a bigger problem. In 2004, a PhD student Jodie Lane died while walking her dogs through the slushy sidewalks of New York City. A metal sidewalk plate had become energized at 57 V, due to the corrosion and insulation failure of an antiquated and poorly maintained wiring system beneath the sidewalk that she happened to be walking on.
Other major cities with aging electrical infrastructure have caused serious injury and even death to dogs that were electrified by sidewalk plates.
For the past 40 years in the dairy industry, stray voltage has been a serious issue, where cows feel the effects and they result in lower milk production. Dairy cows are extremely sensitive to electricity. Generally, they will start to notice currents flowing through their bodies at levels between 0.001 and 0.002 A and subsequently produce less milk each day, as well as suffer additional health problems, such as mastitis. At higher levels, they may die. In 2008, a dairy farmer from Wisconsin successfully sued an electrical utility for $2.3 million over the stray voltage issues from which his cattle had suffered for at least 20 years.