Touch and step potential relates to how personnel may or may not be electrocuted when any part of a crane or load contacts an energized power line. In short, this is the case of “a bird on a wire.” A bird lands on an energized power line and is not electrocuted because the bird is only touching one power line (one potential) and not another potential or ground.
When any part of a crane, load line, or load (object) contacts energized power the crane will become electrified and the ground around the crane will also be electrified by the line voltage.
“Ground Gradient” is the voltage in the ground around the crane and it dissipates over distance away from the crane.
“Ground Potential Zones” are the zones around the crane that have a different voltage. They are completely invisible and very dangerous.
“Step Potential” is the voltage between a person’s two feet when they are standing within the ground gradient. A person could be at risk of serious injury or death simply by standing in the ground gradient area.
“Touch Potential” is the voltage between the energized object and the hand(s) of a person in contact with the object. A person could be at serious risk of serious injury or death by touching the crane or load.
The following illustration depicts how touch and step potential areas are created when a crane contacts an energized power line.
This illustration is a representation only and there is no way of knowing where potential areas will start, how they will form or where they will end.