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Am 17.05.2010 15:19, schrieb Warp:
> Aydan<hes### [at] hendrik-sachse net> wrote:
>>> The most common one being "the voltage is high, but the current is low",
>>> which don't make sense.
>
>> It does make sense if you know that a voltage source always has a series
>> resistance. The series resistance of the high voltage generator is in the kilo
>> ohms, whereas the series resistance of a mains supply is in the single digit
>> ohms or below.
>
> But the voltage difference is between the wire and the ground, and
> there's nothing else between them than the body of the person touching
> the wire.
>
> The current *is* very high. But only for a really small amount of time.
> It's not the current that kills you (as the saying goes), but the power
> transfer (the amount of current over time). I think the unit is Watt.
Note that the probability that you're making contact with the cattle
wire at the very moment that a pulse has just started is /very/ low.
In most cases, the person is already connected when the generator
"fires", so the voltage will not even build up to the maximum of
/static/ electricity the generator could provide.
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Am 17.05.2010 14:44, schrieb Warp:
> Thus I think I wouldn't be really wrong when I say "it's not the current
> that kills you, it's the electrical power transfer (over time)".
No, normally not.
Electrical power transfer /per se/ can kill by either electrolysis or
excessive heat.
Most people killed by electricity die of cardiac arrest though, which is
caused neither by current nor by voltage, but primarily by a "suitable"
frequency (though of course a certain V=I*R threshold must be exceeded
as well).
Mains does not provide enough power to do much harm via /power
transfer/, even with prolonged exposure: While it typically does cause
burns at the point of contact, it takes high-voltage lines to inflict
really serious burns - and even then they're not necessarily fatal.
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"Fredrik Eriksson" <fe79}--at--{yahoo}--dot--{com> wrote:
> > Any ideas what is physically going on here?
>
> http://en.wikipedia.org/wiki/Solar_chimney
>
Thanks. This has to be what is happening. What I thought I heard described to me
didn't involve open air flow but a closed pipe. Either the guy didn't explain
it well or I misheard.
I do have two patents on thermoelectric (Peltier) cooling of electronic devices,
FWIW.
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Warp wrote:
> because it will be I = 40kV/R, which is much higher than with a wall socket,
> where it's I = 230V/R.
You're assuming the same R in both cases here, also. However, with a wall
socket, R is the resistance of the human, while with the fence, R is the
resistance down to the ground, which includes shoes, grass, perhaps gloves,
etc. Also, if you grab the fence with both hands, you're not going to get
current across your heart; at least, not like you do with a socket.
--
Darren New, San Diego CA, USA (PST)
Ada - the programming language trying to avoid
you literally shooting yourself in the foot.
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clipka <ano### [at] anonymousorg> wrote:
> Note that the probability that you're making contact with the cattle
> wire at the very moment that a pulse has just started is /very/ low.
You make it sound like touching the fence is about the same as touching
a 1.5-volt battery poles. Wouldn't that kind of defeat the whole purpose?
--
- Warp
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Warp wrote:
> clipka <ano### [at] anonymousorg> wrote:
>> Note that the probability that you're making contact with the cattle
>> wire at the very moment that a pulse has just started is /very/ low.
>
> You make it sound like touching the fence is about the same as touching
> a 1.5-volt battery poles. Wouldn't that kind of defeat the whole purpose?
The farmer doesn't want to kill the cow. He wants to tingle the cow enough
that the cow learns not to lean against the fence.
--
Darren New, San Diego CA, USA (PST)
Ada - the programming language trying to avoid
you literally shooting yourself in the foot.
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On 17-5-2010 14:07, Stephen wrote:
> On 17/05/2010 12:51 PM, Warp wrote:
>> For example, ask anybody, an expert or layman, why you can die from
>> touching an electrical wall socket (which has at most 230 volts), but
>> usually not from an electric cattle fence (which has tens of kilovolts)
>> and you won't get a straight, rational answer. I have yet to get a
>> proper answer from anybody (which wouldn't seem to violate the basic
>> "U=RI" formula).
>>
>
> It is all to do with current and the path it takes. Cattle fences have a
> limited amount of current and it is dc. Domestic supplies are ac and
> although the current is limited it is in the region of amps. It is the
> current that kills you. More importantly id the current passed through
> your heart the ac component disrupts the electrical signals to the heart
> and in the heart so it starts to fibrillate that is the signals to
> better as it is his subject.
>
A major factor is the 50 (or 60) Hz. If you stimulate a muscle it will
twitch. If you stimulate it again shortly after that, it will twitch a
bit more. The way to let it contract the most is by stimulating it
rapidly at a frequency of about, you guessed it, 50 Hz. So the frequency
at which you need the least power to kill someone is 50 Hz. 60 is not as
effective, but it comes close. Connected to that a bit of advise: if you
want to test if some wire is life with your bare hands (in general:
don't), use the backside of a finger. Then if it is, your muscles will
contract and pull the finger away from the wire. Never use the inside of
your finger and certainly never grasp a wire, then muscle contraction
will increase your grip.
The best way to not kill a person is by using MHz frequencies, then you
have the skin effect, all current flows only on the outside. If you have
a generator that generates that sort of electricity you can safely touch
the electrodes even if there are arcs of ten centimeters between the
electrodes.
A defibrillator gives a short 'DC'-pulse that stimulates all cells in
the heart at once, and resets them. Hopefully the heart will then reboot
gracefully. As a side effect all other muscles will also contract, which
explains the strange movements. Sometimes the patients are also a bit
disoriented afterwards, as if awaken rudely from a dream. There have
been occasions when we had to dive on the patient to keep him on the
table, because they definitely wanted to step out of bed. Which is not a
good idea if there are still all sorts of wires connected and catheters
inserted into the bloodstream.
A well timed defibrillator pulse delivered to a not fibrillating heart
might actually induce fibrillation. That is why you should not touch a
person that is being defibrillated (apart from being painfull
experience). Funnily the same holds for a hit on the chest. There are
cases of people hit by a baseball in the chest at precisely the right
moment at the right place that died from ventricular fibrillation. And
OTOH the precordial thump was a procedure sometimes used before the
defibrillator to stop fibrillation.
Does that somehow answers some questions?
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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > clipka <ano### [at] anonymousorg> wrote:
> >> Note that the probability that you're making contact with the cattle
> >> wire at the very moment that a pulse has just started is /very/ low.
> >
> > You make it sound like touching the fence is about the same as touching
> > a 1.5-volt battery poles. Wouldn't that kind of defeat the whole purpose?
> The farmer doesn't want to kill the cow. He wants to tingle the cow enough
> that the cow learns not to lean against the fence.
Hence 1.5 volts isn't going to do it.
--
- Warp
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On 5/17/2010 5:07 AM, Stephen wrote:
> On 17/05/2010 12:51 PM, Warp wrote:
>> For example, ask anybody, an expert or layman, why you can die from
>> touching an electrical wall socket (which has at most 230 volts), but
>> usually not from an electric cattle fence (which has tens of kilovolts)
>> and you won't get a straight, rational answer. I have yet to get a
>> proper answer from anybody (which wouldn't seem to violate the basic
>> "U=RI" formula).
>>
>
> It is all to do with current and the path it takes. Cattle fences have a
> limited amount of current and it is dc. Domestic supplies are ac and
> although the current is limited it is in the region of amps. It is the
> current that kills you. More importantly id the current passed through
> your heart the ac component disrupts the electrical signals to the heart
> and in the heart so it starts to fibrillate that is the signals to
> better as it is his subject.
>
Mind, a 9 volt battery will do the same thing, but you have to have
direct contact to your insides, since the skin has too much resistance.
Apparently, there is a standing rule on ships that you *do not* stab
yourself with leads, connected to a 9 volt battery, precisely due to
some moron trying this. Then again, I may just be propagating a rumor of
something that happened. But, someone who was in the military told me
about it.
--
void main () {
if version = "Vista" {
call slow_by_half();
call DRM_everything();
}
call functional_code();
}
else
call crash_windows();
}
<A HREF='http://www.daz3d.com/index.php?refid=16130551'>Get 3D Models,
3D Content, and 3D Software at DAZ3D!</A>
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On 17/05/2010 8:21 PM, andrel wrote:
> A defibrillator gives a short 'DC'-pulse that stimulates all cells in
> the heart at once, and resets them. Hopefully the heart will then reboot
> gracefully
As a side note I was taught that it was important to remove any metallic
body jewellery from around the chest area before using a defibrillator.
Ouch!
Another point about electrocution is that mains voltage is not always
and one 800V dc that really woke me up. Insulating footwear is a
lifesaver. :-D
--
Best Regards,
Stephen
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