A common misconception about electrical devices is that the higher its voltage, the more dangerous or deadly it is.
This is a mostly false way of thinking. What kills a person is not coming into contact with a high voltage device but rather, the current that runs out from it and through the body. Current is measured in amperage, and the heart begins to fibrillate when exposed to current measured at more than 100 milliamps. Putting this into perspective, it takes 1,000 milliamps to equal a single amperage.
The most obvious way to explain this understanding is to use high voltage power lines as an example.
The reason high voltage lines are considered unsafe is because of the high currents they carry. However, if a bird lands on a high voltage power line, it’s not affected. To understand this, we need to go over a few things:
Electric current flows only when there is a potential difference between the starting and ending points of the path; that is, electric current does not happen by itself. There needs to be voltage, or a potential difference, across a given path, and electrons flow from high voltage starting points to low voltage end points.
Also, for the electrons to flow, the path needs to be closed. This brings us back to the bird landing on a power line. Its left foot and right foot are grabbing the wire, thereby making a closed path. So why doesn’t it get electrocuted? To understand this, you need to know about voltage drop. Its formula is isv=iR, where, “i” is the current and “R” is the resistance of the conductor. Generally speaking, the resistance of the power line between the bird’s legs is negligible; in fact, it’s pretty close to zero. Let’s say the voltage at the left leg is 11,000 volts, then the voltage at its right leg is 11,000 volts as well. This means there is no voltage drop in the line which, in turn, means the potential difference “V” across the crow’s legs is equal to zero (11,000 minus 11,000). That being the case, current is unable to pass through the crow.
When it comes to humans, a person can hang from a single power line with their hand(s) and not be electrocuted for the same reason as the bird example described above — the potential difference in the closed path is nearly zero.
When the person hangs from the wire and puts their feet in the ground, they will be electrocuted. This is because the ground is considered to have “zero potential”; as such, the potential difference between the person’s hand and leg will be equal to 11,000 volts (11,000 from the wire minus 0 from the ground).
Now, it’s worth noting that power lines often come with more than power line in a run and generally speaking, they’re alternating current lines, differing by varying degrees in phase. This means that at any given moment, the voltages of the various lines in a run are not equal. So, if a person were to grab on to a wire with one hand, and another wire with another hand, they would be electrocuted by the voltage difference between the lines.
To further understand how electrocution works, check out this very informative (and funny) clip below:
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