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 MIL-HDBK-419A
2.8 OTHER CONSIDERATIONS.
2.8.1 Surface Voltages Above Earth Electrodes. Very large currents can be conducted into earth electrodes
whenever power line faults or lightning strikes occur. As a result, there is a substantial voltage developed at
the surface of the earth near the electrode; this voltage varies significantly with distance from the electrode
connection point. The voltage difference between two points about three feet apart on the surface is the "step
voltage", i.e., it is the voltage level between the feet of a person standing or walking on the surface.
2.8.1.1 Step Voltage Safety Limit. The maximum safe step voltage depends upon the duration of the
individual's exposure to the voltage and upon the resistivity of the earth at the surface. The maximum safe step
voltage for a shock duration of from 0.03 to 3.0 seconds has been expressed (2-3) as
2-47
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