Electrical step potential

During a ground fault, current flows through the grounding system to a ground rod or some type of
system ground (steel structure, guy wire) seeking a return to its source. This current flow could possibly
exist in, or along the surface of the ground for quite some distance around the point where the earth
becomes energized. The current will follow, as nearly as possible, the conductors supplying the fault
current. Step potential is caused by the flow of fault current through the earth. The closer a person is to
the ground rod or grounded device, the greater the concentration of current and the higher the voltage.
The current flow creates a voltage drop as it flows through the earth's surface and a person standing with
their feet apart bridges a portion of this drop thus creating a parallel path for current flow as seen in the
these two illustrations in Figure 3

The wider apart a person's legs are, the larger the voltage difference across the body. Protection from
the step potential hazard should be to stay in the zone of equipotential while working. Simply being
alert to this hazard is the best defense. For this reason, unqualified personnel standing on the ground are
cautioned to stay clear of structures.
This means that a person standing near the point where fault current enters the earth may have a large
potential difference from foot-to-foot. The potential difference over the same span will be less and less
as the span is moved away from either the fault current entry point or the fault current return point at the
source.