What is the step voltage?

Pillars with wires of overhead power lines have become so familiar attribute of the landscape of the modern world that many of them simply do not notice. Despite the high arrangement of the conductors, preventing accidental contact, they, nevertheless, conceal a potential danger. Everyone remembers the situation from childhood, when parents, seeing such a ragged wire lying on the ground, tried to bypass this place "the tenth way". Due to this, it is possible to avoid electric trauma, since the step voltage with distance decreases. We all know that you can not approach a broken wire. However, what is the step voltage is known only to people with electrical engineering education. In this article, let's try to understand this issue in more detail, explaining, literally, "on your fingers".

So, the step voltage is the potential difference between the legs or, which is also true, between two (or more) points located one from the other at a distance of a step. When explaining many processes in electrical engineering, they often resort to an analogy with water. Indeed, in some cases, the comparison of the electric current and water is completely permissible, since it simplifies the understanding of the processes occurring. So we will proceed.

Imagine that one of the poles of the power line broke off and one end fell on the ground under the voltage wire. If the wire is a pipe, and the current is water, a puddle will appear at the point of contact with the ground. Its diameter is a zone of spreading, in which a person can wet his feet. The puddle is formed because water can not all be absorbed instantaneously into the soil. The value of the spreading zone depends on the amount of water passing through the pipe per unit time.

Now back to electricity. The voltage source creates a potential difference between the two points of the line, the higher the voltage and the current value, the wider the danger zone around the broken wire. The appearance of the "puddle" is due to the high ohmic resistance of the soil: with an effective ground loop (according to the PUE 4 ohms), the spreading zone is minimal or completely absent.

Imagine that next to the ragged wire is a man. Due to the distance between the feet, a potential difference appears. And because of the resistance of the body - and the electric current. In fact, this means getting electric trauma. And, if after an electric shock a person falls (completely or on hand), this only aggravates the situation, since the step voltage increases. In addition, if the current flows through the "leg-foot" contour in the vertical position of the body, then after the fall other chains are formed that can pass through the heart, posing an immediate danger to life. It's easy to understand that animals (cows, bears, horses) that fall into the current spreading zone are more at risk than humans, since they have more distance between the forelegs and hind legs, and therefore the step voltage is much more dangerous.

From all that has been said, we can draw several conclusions:

• If the current flows from the broken wire (or other malfunction), do not panic and run. When running, the distance between the soles becomes larger than with the step, respectively, the potential increases. Moreover, since a person tries to retire from a current source, then the voltage of the step becomes even more dangerous;
• The shape of the spreading zone may differ from the circle due to differences in soil conductivity.

To leave the area of action of the step voltage, you can use non-conductive material (for example, a thick dry board); Jumping on one leg (in this case there is no potential difference); Or slowly get out, folding your feet together.