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| If the electrical energy is outside the wires, how is insulation protecting us? |
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| SiliconWizard:
So then, what is energy? ;D |
| aetherist:
--- Quote from: typoknig on April 01, 2022, 03:13:06 am ---This question stems from the Veritasium video (below) and Dave's analysis of that video (also below). Both Derek (8:56 in his video) and Dave (5:17 in his video) say that the fields carry the energy. I am not disputing this, but what I don't understand is why am I not getting shocked when I grab an insulated piece of Romex if all the energy is "outside" the wire? --- End quote --- The answer is that Derek & Dave & Nick & Mehdi & Brian & Bob & Co are all wrong. The energy is not (wholly) in the fields. If u have to touch the wire (or nearly) then the energy is due to something in or on the wire. Old (electron) electricity says that the energy (force) is carried & transmitted by slowly drifting electrons inside the wire. My new (electon) electricity says that the energy is carried & transmitted at the speed of light via electons (photons hugging the wire) on the surface of the wire. Both electricitys satisfy the fact that insulation prevents electrocution. The problem in a way involves the terminology. The electric energy is produced somewhere somehow. It is located somewhere in someform. It is carried by something in someway. And all the time or sometime electric energy is also radiated as em radiation, & is available if u have the means to take advantage of it. The em radiation is to some extent a minor form of electric energy in its own right, but em radiation is mainly a form of transmission of electric energy. If u tap into this em radiation then u can extract electric energy from the wire, where the major part of the electric energy lives. The human body can't readily tap into the electric energy on the wire via the em radiation. We have to touch the wire. Even then we can't readily extract much electric energy (ie get a big shock). To get a big shock we have to also touch the ground, or another wire. Derek & Dave & Nick & Mehdi & Brian & Bob & Co are all wrong. Electric energy is in or on (i say on) the wire. |
| T3sl4co1l:
Mains transmission lines carry the superposition of a multitude of wavefronts. Each increment of wave energy is imperceptible, and most of them cancel out, hence why little power flows until a load is connected, and even then only what the load needs, not the full, whatever, 120V / Zo (which for romex is ballpark 100 ohms) that a single full-step wavefront would deliver. Waves are indeed perceptible, but they need to be much more intense: ESD for example. The spark from touching a grounded object propagates over and through your body, near the speed of light, giving a risetime of some nanoseconds. The peak power is in the megawatts, enough to ionize air (hence the spark), and some skin around the contact area (not enough to notice from single hits, but the burn from multiple hits can be particularly destructive, e.g. RF burns). Over a longer time scale, as things settle down, the charge delivered by this pulse causes ionic separation/motion in your tissues -- evident as the intense pain and sudden movement as it affects your nerves and muscles. The human body in general is rather insensitive to electromagnetic fields, actually. Fortunately, I guess. Aside from visible light of course, and from frequencies low enough to affect the nervous system directly (<kHz) -- which by their nature, are almost impossible to carry through air alone, and need some contact to deliver real charge. Note we can reduce the transient model to an average equivalent at low frequencies. And here, it simply suffices to note that, the capacitance between say your finger and the wires in a piece of romex, is a couple pF at most, and at 120 even 240V, is just some microamperes, well below sensitivity threshold. Tim |
| RJSV:
Took College course, along those lines. Please also see 'Fields and Waves in Modern...Electronics' By Winnery and Van Duzer. (spell check!) It is more advanced than I can handle, fully, but in catagory, of, like 90 % beginning and medium level physics. The main gist, of any energy flow, by itself without conductor, is a kind of 'chasing own tail' dynamic: The changing electro field causes, or generates, a resulting changing magnetic field. That then continues, as that changing magnetic field, in turn creates a changing electric field. That perpetuates, and all the 'Maxwell's equations' describe that, in calculus 'rates' of change, 'd X /dt', for the two field types. That, of course, relating directly to 'c', the standard speed of light. Light waves being EM waves, of course. You could, I guess, say that the 'magnetic field is time-varying, this inducing an electric field.' Then, just say 'This field pushes electrons, in the nearby conductor. Nearby insulation, not so much resulting flow, (from the e field). Ok, then just say "That new electric current then, being time varying, will cause a NEW magnetic field, to expand around the insulated conductor." That gets you to perceive the continuous, remake of those EM fields, that's the 'propagation' over nearby distance, all happening at light-speed. |
| RJSV:
I almost have it right. As some others here, are almost correct. I'd have to say: That the energy is partially held, in the wire, by the current , let's say it comes from 1 MHZ signal generator, 1 volt pk to ok. As that goes down the wire, as mentioned, d V/dt causing d u/dt (magnetic), causing, yet more d V/dt, in circular fashion, I think that cyclically, the energy IS not right in the wire, but soon will be. Looking at one single point, you observe the wax and wane, SINE shaped voltage wave, moving past your sample point. Plus with magnetic sensor a similar SINE wave, I believe 90 degrees offset, (hypothetical 1 Mhz). However, energy does not travel speed of light, when carried by a cable, coax or twisted pair...EM speed is something like 70 % of 'c'. I guess, that slower speed is a kind of phase-lag, as the free space EM wave has to charge up each little segment if the cable, as it goes...but that's not a professional talking. The experts talk, also, about 'phase' velocity vs wave speed...way over my head and pay scale. |
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