I never understand why electric shock happens if I'm connecting to ground by isolated material.

Let's consider an example with monophase 220V electrical system electrical shock while I'm wearing rubber shoes and touching a stripped wire.

With this circuit an electrical shock happens: electrical system- stripped cable - hand/body - rubber shoes - ground- electrical system- ...

However if I swap the order touching the wire with a shoe in my hand there will be no current through this circuit: electrical system- stripped cable - rubber shoes - hand/body - ground- electrical system- ...

The same considering the ceramic tile on the floor. This isolate me if I put it between the wire and my hand, but not if it is between my foot and the ground.

  • 1
    \$\begingroup\$ With direct contact to the wire you are forming one plate of a human sized capacitor. \$\endgroup\$ – Majenko Oct 11 '14 at 10:48

It boils down to current distribution, but let's start from the beginning.

In both cases you form a circuit with several elements in series. Some of them have excellent conductivity, like copper wires. You are of meager conductivity, but your shoes and ceramic tiles have even worse conductivity, they are dielectrics. As the dielectrics have contact to or are in between conducting elements in a geometric relationship they form capacitors. This circuit consisting of capacitors and resistors permit AC current to flow. Aside from some other effects the current should be the same order of magnitude in both configurations.

What's the difference now between both cases? When touching the copper wire you form a conductive connection with a very small area for the carriers to pass. As two conductors connect, there can't be a strong electric field either. Due to the small area the current density maximises and you can sense it. n.b.: you can't sense it at your feet, can you?

The other case differs as you touch a dielectric. This dielectric differs from the surrounding air but not very much to change the electric field dramatically. Hence the electric field vectors connect to your skin perpendicular and with merely unchanged field strength. At your skin the electrical surface charge influenced by the field causes a current, but this time distributed over the surface of your hand. You can't sense it.

  • \$\begingroup\$ Are you saying that the current throw this circuit is the same in both cases but in the first case I feel it and in the second I don't? Something changes with DC? \$\endgroup\$ – Tobia Oct 11 '15 at 10:20
  • \$\begingroup\$ Yes, that's what I think considering the experimental setup. DC will be more difficult to sense, because alternation of current is in my experience less tickling. \$\endgroup\$ – Ariser Oct 12 '15 at 13:16

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