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# Stray Voltage Field Guide - page 2 / 8

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hoof to another was 3.7 milliamperes. It thus took about 10 times the current to elicit a response from a cow than from a person. This is mainly due to the smaller cross section of humans when compared to cows.

While the resistance of cow and human tissues is similar, the contact resistance is generally lower for cows than for humans, particularly if cows are in a wet environment. The resistance of a cow’s body plus the contact resistance with the floor is commonly estimated as 500 Ohms. The resistance of a human can be as low as 1000 ohms for wet hand - foot contact to higher than 10,000 ohms for dry hand - foot contact. The contact voltage to produce sensation can therefore be higher for humans than for cows, depending on the conditions of the contact points. In most situations cows are less sensitive to current and more sensitive to voltage than people are.

Average steady 60 Hz rms current to elicit response Average steady 60 Hz Voltage to elicit response

Cows 3.7 mA

Humans 0.45 mA

1.9 V

0.9 - 9 V

# Phase Duration and Frequency

There are three broad classes of contact voltages that animals encountered in animal environments.

• 1.

60 Hz Steady State and Motor Starts

• 2.

Fencer Transients

• 3.

Switching Transients

Animal and human sensitivity is very different for these three categories of voltage and current. The easiest way to determine the ability of an electrical pulse to excite nerves is to specify its phase duration and peak current. The following examples will help to explain these terms.

Electric power is distributed as Alternating Current (AC). The voltage and current alternate between positive and negative values at a frequency of 60 times per second or 60 Hz. Current flows back and forth in a wire, rather than in a continuous flow like water in a hose. It takes 1/120th of a second, or 8.33 milliseconds (or 8,333 microseconds) for the voltage to cross zero, reach its peak value and return to zero. The time between these two zero crossings is referred to as the phase duration. A recording, typical of that obtained with an oscilloscope taken in a cow contact location using a 500 Ohms shunt resistor, for steady 60 Hz voltage is shown in Figure 1a. The time scale indicated is 20 milliseconds per division. The phase duration can be estimated as somewhat less than ½ of a division. This corresponds to the expected phase duration of 8.3 milliseconds for 60 Hz. The voltage scale indicated is 1 Volt per division. The peak voltage of this waveform is 2 Volts (note all peak voltages cited in this paper are from zero to peak, NOT peak to peak). This would correspond to an rms value of 1.4 Volts.

The distribution of behavioral reactions for dairy cows is shown in Figure 2. Cows are somewhat more sensitive to single hoof-hoof exposure than to muzzle - hooves exposure

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