Awareness of step and touch potential, caused by ground potential rise, is important for anyone working on high-voltage power transmission systems. In a typical SNT application, the transmission line is de-energized and is bonded to the tower to be safe to work on.
source/image(PrtSc): safique memon
However, the transmission line itself acts as a very large antenna, and can pick up large amounts of energy which must be shunted to earth ground. And if the tower ground is faulty, the ground potential may rise and a dangerous condition can result.
Step-Potential – Step potential is the potential difference between the feet of a person standing on the floor of the substation, with 0.5 m spacing between the one step, during the flow of fault current through the ground system.
Touch-Potential – Touch potential is a potential difference between the fingers of a raising hand touching the faulted structure and the feet of the person standing on substation floor. The person should not get a shock even if the ground structure is carrying fault current, i.e.; the touch potential should be very small./circuitglobe.