Stray Voltage Field Guide
Douglas J. Reinemann, Ph.D. Associate Professor of Biological Systems Engineering University of Wisconsin – Madison
I. Introduction to Animal Sensitivity and Response
The widely accepted understanding of the way that stray voltage affects animals is through nerve stimulation. Nerves communicate through chemically produced electric pulses. A certain threshold is required for these electrical pulses to jump the gap between nerve cells. If the charge is below this threshold, no information or sensation will be transmitted by a nerve cell. These pulses act to communication between organs, contract muscles or transmit sensations of temperature, pain, and touch.
Externally applied electric current can produce the same sensations as the electric pulses produced by nerves. Externally applied current will spread out through the various tissues in the current pathway. It produces a current density depending on the voltage applied and the path through the body between contact points. A tingling sensation is commonly produced by contact with low-level electrical currents. As the current density increases muscle contraction occurs. This may result in a “quivering " sensation as alternating current causes muscles to alternately contract and relax. This level of current is normally perceived as annoying or painful. These low-level currents are not thought to produce any lasting damage to tissues. The main concern for animals is the behavioral responses to these sensations.
In order for electrical current to cause adverse animal response, it must first be of sufficient level to cause annoyance to the animal. The critical factors in ability of electric current to cause annoyance are the amount of current flow through the animal (and resulting current density) and the phase duration or frequency of the current (see section II).
The second consideration in the ability of electrical current to cause adverse animal response is the conditions under which the animal is exposed. These conditions include the location and number of times per day that the electrical event occurs (See Section III).
II. Nerve Stimulation and Annoyance Current Flow
Animal tissue generally behaves according to Ohms law. At any fixed frequency the current flowing through animal tissue will be directly proportional to the voltage across it and inversely proportional to its resistance. The resistance of animal tissue decreases at high frequencies.
Cows present a larger cross sectional area than humans so it requires more total current to produce the same current density. In a study of the sensitivity of cows and people to 60 Hz current it was found that the average current perceived by people when applied to two adjacent fingers was 0.37 milliamperes, with discomfort noted at 0.45 milliamperes. The average current for which cows showed a behavioral response, when applied from one