Energized human body

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chris kennedy

chris kennedy

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Miami Fla.
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60 yr old tool twisting electrician
When one comes in contact with an energized conductor but doesn't complete the circuit back to the source, why don't we feel the sudden change of potential?

Thanks
 
There is a difference in potential between the energized conductor and the floor. Supposing you are standing on a very thick rubber mat and further suppose we can disregard any capacitive coupling between your body and the floor (and other nearby grounded surfaces, such as pipes or metal enclosures). Thus, there is a difference in potential between your body and the energized conductor. When you touch the conductor, your body will come to the level of potential of the conductor, as Chris pointed out. You become energized. But lacking a path for current flow, your body and the conductor simply remain at the same potential as each other. You don?t feel it for the same reason that a bird feels nothing when it lands on an uninsulated transmission line. There is no difference in potential from any point in your body to any other point, thus no current flow, and thus nothing to feel.
 
chris kennedy said:
When one comes in contact with an energized conductor but doesn't complete the circuit back to the source, why don't we feel the sudden change of potential?

Thanks
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Because the symbol for current is I, which is from the French word for intensity, that is, the intensity of the shock.
You have an I less than 1 mA so you feel nothing.

If your body had a capacitance to ground of 20,000 pF, at 60 Hz and 120 V up to one mA might flow and you would probably feel a shock.

It does take current to charge your body's capacitance. If you touched the line at its peak of 170 V and you had a more reasonable capacitance to ground of 100 pF, the charging current spike would peak at 170 V/3K (your body resistance) = ~6 mA but would last only 60 uS.
 
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chris kennedy said:
When one comes in contact with an energized conductor but doesn't complete the circuit back to the source, why don't we feel the sudden change of potential?
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Because current shocks and kills, not voltage.

Voltage is the push, but current is the result.
 
LLSolutions said:
Because you have no potential......
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Yeah, I know, my parents told me when I was very young.


We have all seen video's like this. A great change of potential happens here. So at the moment of contact why don't our arm hairs stand up? Did we not achieve a different potential than the humid air around us?
 
hurk27 said:
I don't think many realize that standing bare foot on Earth we are connected to one side of a transformer or many transformers somewhere, no different then the bird on a wire example.
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I get that part, as we walk our potential is changing slowly with each step. Just trying to understand why we don't feel sudden change of potential.
 
chris kennedy said:
We have all seen video's like this. A great change of potential happens here. So at the moment of contact why don't our arm hairs stand up? Did we not achieve a different potential than the humid air around us?
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Since the arc is continuous the current is continuous and the circuit is line to helicopter-capacitance-to-ground to ground.
If it were DC at high potential in the lines there should be one big arc that dies as the helicopter-ground capacitor is charged up.

If you know the sq. ft. of the helicopter footprint and the height above the ground plane you can calc. the capacitance (the dielectric is air). Then with the line voltage you can calc. the current in that continuous arc.
 
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charlie b said:
There is a difference in potential between the energized conductor and the floor. Supposing you are standing on a very thick rubber mat and further suppose we can disregard any capacitive coupling between your body and the floor (and other nearby grounded surfaces, such as pipes or metal enclosures). Thus, there is a difference in potential between your body and the energized conductor. When you touch the conductor, your body will come to the level of potential of the conductor, as Chris pointed out. You become energized. But lacking a path for current flow, your body and the conductor simply remain at the same potential as each other. You don?t feel it for the same reason that a bird feels nothing when it lands on an uninsulated transmission line. There is no difference in potential from any point in your body to any other point, thus no current flow, and thus nothing to feel.
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Yes, like the show " Toughest Fixes, High Voltage Lines " where the lineman in a faraday suit sitting on a helicopter platform "bonds on" to a 500kv transmission line and lineman, pilot and chopper and all are at same potential as transmission line.:)
 
chris kennedy said:
We have all seen video's like (this). A great change of potential happens here.
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Yes, a great change. HV linemen deal with hundreds of thousands of volts from line to line. That is enough to push an arc across open air, if you get close enough. But open air has a very high resitance, so it would take a very high voltage to initiate such an arc.
chris kennedy said:
So at the moment of contact why don't our arm hairs stand up? Did we not achieve a different potential than the humid air around us?
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Not enough of a difference in potential to force current to flow.
 
The simple answer is you don't have a human sense that registers voltage, so you can't tell when it changes. Obviously, your nerves can sense current.

Mark
 
The Van de Graaff generator puts your hairs on end because you build a directional (positive I believe) magnetic charge which seeks negative charges in the atmosphere. This is distinctly different from storing energy such as the bird on a wire.

The bird begins charging to the new potential as it approaches the wire due to magnetic coupling. On contact the balance of energy is transferred. This is purely energy storage. The amount of energy the body can store is minimal so the inrush is minimal.

This means it takes a fairly significant voltage before you feel the inrush. If the voltage is high enough that you feel the inrush then you are probably in trouble. The inrush is current trying to cook cells.

If you ever grabbed a wire and felt a tingle in your fingertips on contact then it MIGHT mean you just got charged to a new voltage potential. Touching something at the same time would be very bad.
 
chris kennedy said:
When one comes in contact with an energized conductor but doesn't complete the circuit back to the source, why don't we feel the sudden change of potential?

Thanks
Click to expand...
The reason why you don't feel the change is because your body is not sensitive enough to detect it. Any change in potential (voltage) requires a transfer of electrons. For low voltages, this transfer of electrons is relatively trivial and not noticeable, but it still happens.

I know you were around back when this "helicopter" example came up a few years ago, so you can go back and read some of that discussion. (I don't feel like doing a repeat performance--although it was fun at the time.)

We are constantly experiencing different potentials on our bodies every day, simply because the absolute voltage of our planet is constantly changing as energy is absorbed and lost. We (our planet) are like a bird on a wire. Our potential is constantly changing, and we absorb and lose electrons in the process, but the rate of change is trivial compared to when we are not isolated from a different voltage reference (i.e. current flow).

You're not going to "feel" this charge/discharge when the difference is only a few hundred volts, but you will feel it when the charge/discharge is in the hundreds of thousands of volts. That's why the helicopter arcs, not because of capacitive coupling to the source.

You don't feel the build up of charge in your body as you walk across the carpet, but you do feel it when you contact a voltage potential significant enough to result in a rapid discharge.
 
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