Electronic – Theory: Can power cables induce AC voltage in human body

accapacitortheory

In a demo video (which I unfortunately can't share) a man makes the following setup:

  • Multimeter on 200 V AC settings with one pin in the ground socket of a conventional mains power socket.

  • Right hand holding the other pin

  • Left hand free to hover over or touch a conventional extension cord (insulated) which is connected to a device with the mains power on.

Then he varies a few things and observes measurements:

  1. Wearing shoes: hovering left hand over the extension cord gives 2~3 V readout. Gripping the cord gives 10 V readout.

  2. Barefoot: hovering left hand over the extension cord gives 0.5 V readout. Gripping the cord gives 3 V readout.

I've been working on an idea for why this happens and I'll propose it here. The point of the question is to understand the theory by either getting your thoughts on my proposal, or your own proposal.

So my thoughts are as follows:

Wearing shoes

  • Left hand and cable are acting as two plates of a capacitor.
  • The human body is not a perfect conductor, therefore there is time for charge to "pool up" in the left hand in a 50 Hz cycle. Therefore when measuring the right hand relative to ground, we see an AC voltage readout.
  • To explain what I mean, I've modelled the human as 3 charge reservoirs interconnected by resistors. The middle reservoir is the body, the left reservoir is the left hand, the right reservoir is the right hand.
  • I also show the flow of charge with a double ended arrow (indicating that it's AC, but slow at 50 Hz)

enter image description here

Barefoot

  • Now there is a larger reservoir to draw from, that is the floor. So the main current flow is between the left hand and feet.
  • Therefore less charge from the right hand reservoir is needed to equilibriate.
  • Therefore the readout is lower.
  • Perhaps the current induced is larger than in the case where he is wearing shoes?

enter image description here

Best Answer

I would forget the pooling theory and model with normal circuit elements. You are mixing static electricity models with discrete circuit models.

With shoes, R4 is nearly infinite.

Barefoot, R4 is smaller, how much depends on the floor type. C2 is larger. Either of these will cause the voltage divider to reduce the voltage on the right hand. It is difficult to determine which is the primary effect.

If you repeated the experiment barefoot standing on a thin layer of mylar you could learn more.

Note that internally, bodies conduct electricity much better than your skin resistance.

schematic

simulate this circuit – Schematic created using CircuitLab

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