Any difference in voltage (Volt) recorded between two points likely to be touched by an animal and which may cause a flow of current which would affect its behavior.
Animals react to the current produced by a voltage and not to the voltage itself. For an animal to react on contact with the two points, the voltage source must generate a current flow of an intensity greater than the tolerance threshold thereof.
In this case, a voltage difference (V) of 0.500 Volt is measured. Knowing that the average resistance of a cow (R) is 500 Ohms, we deduce that the current generated in the body of the cow (I) is 1 milli Ampere (1 mA).
I = V / R = 0.500 Volt / 500 Ohms = 0.001 Ampere or 1 mA
It is this generated current (1 mA) that affects the behavior of the animal and not the current flowing in the metal parts (20 mA). Measuring the current in metallic parts is therefore of no use.
It is recommended to keep this voltage difference (V) below the generally recognized tolerance threshold of 0.500 Volt.