Re: Electrify Vehicle Body?

I also agree, they feel nothing at all.

Another true story and actually one my college professors papers.

Cows were dying at a farm, but no other animals and people were not being harmed either. No diseases were found. It was later discovered that on the farm, there was a transformer on a pole. Appearantly this was broken and the pole was 'live' relative to some location across the farm. This created an electric field. Due to the seperation of the cows legs (front to rear), this small trickle current would cause some of them to die over time. it wasnt enough voltage to harm any other creatures.

This was in Texas.

Similar to the phenomon you see with

in message news: snipped-for-privacy@texas.net...

To drugged-up people, too:

Speaking from personal experience, one more reason DC is worse; where AC reverses 120 times per second (for 60 Hz) and crosses zero 120 times per second, giving muscles half a chance to let go, DC seems to hold muscles in the same position, making it less likely you'll get away. I used to get 25KV from televisions all the time, 110VAC fairly often as well, but the absolute worst and most painful shock I ever got was 300 VDC.

Not just for lightning. We got training from Commonwealth Edison a while back in which they said if you absolutely had to go in the direction of a power line, don't have both feet on the ground at the same time. A couple of experienced linemen there said they'd experienced voltage from foot to foot (via crotch), higher as they got closer.

okaaay....

Now, I will add my observation. When you have a bird standing on an electrical wire that is NOT insulated, you have a wire with a parallel resistor attached to it.

So, let me see if I can do ascii art:

-------------------------------------------wire B+ |v^v^|

not very good, but, presume that is a resistor B+ is the wire it is attached to.

now the question is...is there any current passing through the resistor, when there is current flowing through wire B+, or even voltage on wire B+

well, yes.

"The same voltage exists across each branch of a parallel circuit and is equal to the source voltage."

So, if there is 50,000 volts on that wire, there is also 50,000 volts on the bird! But voltage isn't what kills...current is.

We use the formula:

Now since the resistance of wire B+ is so low (R1) relative that that of the resistor in parallel with it ( the bird, attached by its feet )(R2), almost no current flows through the bird. But certainly SOME current flows through the bird.

Presume the impedance of the bird to be at least a few megohms. If it has wet feet, it could go lower than that.

The one resistor being: the impedance of the wire between the birds feet, the second resistor being the bird itself.

the impedence for the wire is almost zero ohms, fortunately for the bird.

If you plug in the numbers, where R1 is almost zero, being conductive wire, you know...there is about milliamperes at most passing through the bird, certainly less than 35 milliamperes, since anything above that will lock the muscles of the bird's feet to the wire and it wouldn't be able to fly away.

Now you say, you need a ground for the bird.

Well, it is capacitively *coupled* to ground, as determined by the capacitance of the air/moisture between the bird and the other side of the line which is the neutral. So yes there is a complete circuit there, and the bird is part of it. Fortunately for the bird, its feet provide some insulation.

Lg

There is a size/surface area issue. For DC, indeed there needs to be a complete physical path. This is not true for AC, however. A capacitor conducts AC. Every object has a certain capacitance to free-space, which is essentially ground. This capacitance depends on the area and geometry of the object. I forget what the capacitance of the human body is, but it its certainly not zero. Now, it is low enough that the amount of current flow via this path is usually not fatal with a 110 contact (note I said USUALLY), but you can indeed feel it. With high tension lines, however, the amount of current flow through that capacitance CAN be fatal to humans, and sometimes large birds alighting on high tension lines are fatally zapped.

I suspect that birds can feel the influence of the line, and may have enough presence to not land on one with too high a voltage when they feel the influence.

Incidently, the capacitance to free-space of a car body is VERY large, and significant current flows from a power line through a car, even though the car is insulated by the tires from direct contact with ground. That is, through the skin of the car. Cars with metal roofs are a somewhat effective faraday cage (no internal fields), but not completely (too many windows and openings which allow partial penetration of fields).

The POINT is that powerlines that birds sit on are operating under totally normal loading conditions. At those loading conditions, a 14kV (typical urban) power line *might* be carrying a total of 100 amps of current. Thats the same as a single *house* feed at 220v. Through a big fat cable of a wire. The voltage drop per foot is *tiny* and a bird with a 30-foot legspan wouldn't see half a volt across its feet.

Basic circuits is actually EE 411. I took that one on the way to two degrees in EE.

So what. We all have a molecule or dozen of cyanide floating around our bloodstreams, too. We don't die from it, or even notice it. When something is so vanishingly small, why consider it at all? Especially when another effect (a bird shorting across two wires or to ground) has a HUGE effect.

ROFL! No one on the planet uses anything else for wide area power distribution, and you call it a "dumb American choice." That's rich. Ships and airplanes use 400Hz because the equipment can be physically smaller and lighter, but if you tried to use 400Hz for terrestrial power distribution, losses would go up astronomically. There are very solid engineering reasons to use a frequency between 30 and 100 Hz for terrestrial power distribution its not a "dumb choice" of any nationality. Its physics.

Good grief. What a silly statement. Yes, electrophoresis occurs in semi-conductive ionic solutions, but it takes hours in perfectly still medium for chemicals to begin to separate significantly! In a LIVING organism its so slow that blood and lymphatic circulation are FAR more than adequate to prevent it from causing any sort of chemical stratification. I defy you to show me ONE documented example of what you state occuring in a living animal or human.

The REAL dangerous effect is on nerve and muscle impulses. DC will stop the heart, but when the DC field is removed the heart will usually start again if the patient is otherwise healthy and the heart wasn't stopped for too long. That's how defibrillators work, and coincidentally why the old TV trick of some hero using a lamp cord as a defibrillator WON'T work but will kill the patient. AC current doesn't stop the heart cleanly as DC current does, it PUTS it into an unstable fibrillation that the heart frequently WON'T spontaneously recover from.

I've been warned somewhere along the way that tires these days often contain carbon fibers and carbon that make them conductive *enough* to hurt a body.

Congratulations. electricity 101 was a highschool course. Unfortunately I only have a single degree in EE. You may not like my answers, but they are all accurate.

What I said was an answer to a question posed. You can pick from any of

a. They do. Since some current is flowing through them. b. They don't. Since the current is neglidigible. c. Their feet are too close together for the current to be significant.

I'm not a Electric Power Engineer so I don't know. Its what I was told. 60 was more dangerous to the heart.

OK, its just a fun fact I read somewhere.

You dont have to get shocked with some enormous blast to die. A small current that disturbes your heart rhythm is all thats needed. When doing heart surgery, surgeons are reluctant to remove any extra material they find, preferring to tie it off instead. They are careful not to alter the electric signature of the heart and its surrounding area. It can take a while to return to a normal rhythm once the area has been disturbed.

So its not all about blasting someone to cause death. A small trickle current can do it as well. This is why I am reluctant to say the bird is not being shocked.

The kind you get in a box of Cracker Jacks doesn't count, ace.

The current is *which* now? It's "neglidigible"? Put _that_ in your Funk and Wagnall's!

Oh, izzat so? Then expla>>> 50-60 Hz was just a dumb american choice.

You were corrected:

You responded:

Yet you felt very confident that your "answer" was correct, despite it being based on the ignorance you confess here.

Ah, so you're just parrot>>> [DC causes] eventual poisioning due to ionization and movement of

Once again you were soundly corrected:

Then we hear the melodious sounds of frantic backpedalling from your corner, and you say:

Oh, it is? Gee, what happened to those "accurate answers" you were so proud of?

You're reluctant to say something does not happen? That's quite a change from just the other day, when you were stridently insisting that it *does* happen.

You're welcome. Glad to help out, any time.

It is. However, I don't understand how you are applying that to current flow... ???

Electron flow needs a complete path - always. Otherwise there would be no electron flow. A capacitor only appears to conduct AC, it does not really conduct AC.

Ahh, well if I had known Cracker Jacks offered I wouldn't have bothered with the college and all.

Bah, I always spell that wrong. Havent spent enough time to understand the rule about when to add an ible vs. an able. So I just spell it whatever. Engineers can't spell anyway.

Yes, I stand corrected. But that was far down into the discussion. The "correct 'answers'" refer to actual questions asked. Not bonus information.

The answer is accurate.

I'm not a jerk. I don't have problems when someone can show I am wrong. I just accept it.

No. Thats not a change. Shock is relative. If you mean it can kill you, then yes, if you mean it will blast you off of the wire, then no.

You didn't actually add anything except to attempt to belittle me.

Gauss law tells us the charge distribution of a charged body. The gist of it is that like charges repel, and thus the charges will push each other away.

If you have 3 people (assume they are perfect conductors) holding hands, with a total charge of -6.

A-B-C

You end up with -3 in person A and -3 in person C since the charges are trying to run from each other. If they all stay in contact, but person b and c switch, then you will have a charge flow from C into B since B is now on the outside.

This is what happens when you step out of a charged car. You are now on the outside and charges can get away from other charges by entering you.

I suppose you could view a 'complete path' and an imbalance as the same thing.

The generally accepted figure is that a few MICRO-amps flowing through the chest cavity around the heart is sufficient.

The trick is that the skin surface isn't very conductive, so a good bit of voltage is required to push current across that boundary. And once current gets into the body tissues, it tends to spread out so the current through any particular area far away from the point of contact with the external voltage source will be low. If you have electrodes directly on the heart muscle, you can stop the heart with a couple of AA batteries. If you grab two wires, one in each hand and your hands are dry, it takes many times that voltage (and you'll feel pain before the current density in the chest cavity gets very high). If the contact points are one foot and one hand, its even more voltage needed because the path kinda skirts the edge of the chest cavity.

The whole thing is very complicated, and its hard to lay down hard and fast rules. You can't really say "a 12-volt car battery can't kill a person" because under some very odd circumstances it just *might* But its extraordinarily unlikely.

I agree... but I still think the bird is more likely to be "shocked" by capacitive coupling to ground than by the infinitesimal per-unit-length voltage drop along a power line.

I am unable to make any sense of what you are trying to say.

Like charges repel. Give them a way to move further away from each other and they will take it. There is no 'ground' or completed circuit required. Can't explaint it any other way. Its a facet of Gauss law.