General > General Technical Chat
If the electrical energy is outside the wires, how is insulation protecting us?
RJSV:
Ah, thank you, bsfeechannel.
That explanation provides a way, to start thinking about the electric 'Model' for the two cases of contact.
First case being simple contact, with another contact to a ground, or a second metal conductor. That's the more 'classic' case, where you can figure out a clear path, unfortunately going through a person, to wet floor etc.
The other situation, RF, my thought is that you could 'touch' the cable wire, but by way of a bunch of capacitors, conducting current easy due to RF high frequency. So, no need to look directly, for a 2nd conductor to contact...the RF can 'find' that 2nd place, where the RF has little impedance, like an insulated shoe bottom, having enough capacitance to put person in danger, and the person's body then is conductor via the tissues and fluids.
My body model could start there, place a capacitor to ground (wet floor containing steel rebar), and MODEL the body as a resistor, at, say 500 ohms. THEN, on other end, another capacitor, to the cable metal inner wire; that would 'model' the insulation.
Result looks like CAP--Resistor--CAP and then you run your numbers, at RF frequency.
Skin effect, is too complex for me to lecture on, but I can understand portion of others explanation about RF burns. (I think that's in the skin surface, ...a separate consideration, using same word, as skin effect generally for some surface, like a cup or outside of a RF coax.)
That model was very simple, but point being RF doesn't necessarily need a visably 'complete' conductor around the circuit, (to convey the burns).
SiliconWizard:
Well, when you touch an object, I don't think you're ever in full "contact" with the underlying material at the atomic scale. There are a lot more gaps than points of contact, I think. You're just getting "very close".
TimFox:
When human skin touches a metal object, much of the electrical contact is through water (saline solution in sweat).
At the "atomic scale" (0.1 nm) the electrons move about in the environment.
SiliconWizard:
--- Quote from: TimFox on April 04, 2022, 08:42:18 pm ---When human skin touches a metal object, much of the electrical contact is through water (saline solution in sweat).
--- End quote ---
Yes, which is why the impedance directly depends on how dry/wet(/oily...) your skin is.
But that water interface with ions opens a whole other can of worms.
TimFox:
Back in high school, we amused ourselves with "lie detection" by gripping the two probes of a Simpson 260 on its highest megohm scale: the resistance varied considerably depending on the skin moisture content.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version