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Sci.Electronics.Basics -> Human Electrocution: How is the resistance not ridiculously high?
There are 28 messages in this thread.
You are currently looking at messages 1 to 20.
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Author: =?ISO-8859-1?Q?Tom=E1s_=D3_h=C9ilidhe?=Date: 12:05 03-04-08
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I've been doing electronics for three years now but I don't understand
how a person can be electrocuted by touching one part of the circuit
in a mains supply.
If I hold one lead of an ohmmeter in my left hand, and the other in my
right hand, it registers the resistance to be approximately 2
megaohms, which is ridiculously high.
Now if I hold one lead in my hand, and dig the other into the grass,
it doesn't even register -- I may as well be holding the leads apart
in thin air.
Current = Voltage divided by Resistance
Current = 230 volts divided by 2 megaohms = 115 microamperes
115 microamperes is nowhere near enough to electrocute someone.
So lets say I stick a metal rod into the socket on the wall. The
current has to flow thru my hand, down to my foot, thru my cotton
sock, thru my shoe, thru the wooden floorboards, thru the concrete,
thru the clay down to the metal rod we call ground. Now excuse me, but
is that not a RIDICULOUS amount of resistance, up in the gigohms
somewhere?
It may sound like I'm denying that people get electrocuted -- I'm not,
I realise that people do get electrocuted. But I can't for the life of
me understand how enough current can flow, given the massive
resistances that are involved.
Can anyone enlighten me?
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Author: John PopelishDate: 12:40 03-04-08
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Tom=E1s =D3 h=C9ilidhe wrote:
> I've been doing electronics for three years now but I don't understand
> how a person can be electrocuted by touching one part of the circuit
> in a mains supply.
>=20
> If I hold one lead of an ohmmeter in my left hand, and the other in my
> right hand, it registers the resistance to be approximately 2
> megaohms, which is ridiculously high.
> Now if I hold one lead in my hand, and dig the other into the grass,
> it doesn't even register -- I may as well be holding the leads apart
> in thin air.
>=20
> Current =3D Voltage divided by Resistance
>=20
> Current =3D 230 volts divided by 2 megaohms =3D 115 microamperes
>=20
> 115 microamperes is nowhere near enough to electrocute someone.
>=20
> So lets say I stick a metal rod into the socket on the wall. The
> current has to flow thru my hand, down to my foot, thru my cotton
> sock, thru my shoe, thru the wooden floorboards, thru the concrete,
> thru the clay down to the metal rod we call ground. Now excuse me, but
> is that not a RIDICULOUS amount of resistance, up in the gigohms
> somewhere?
>=20
> It may sound like I'm denying that people get electrocuted -- I'm not,
> I realise that people do get electrocuted. But I can't for the life of
> me understand how enough current can flow, given the massive
> resistances that are involved.
>=20
> Can anyone enlighten me?
Do the calculation again but with the other hand on the=20
water tap or the grounded case of an appliance.
--=20
Regards,
John Popelish
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Author: Stephen J. RushDate: 12:54 03-04-08
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On Thu, 03 Apr 2008 09:05:36 -0700, Tomás Ó hÉilidhe wrote:
> I've been doing electronics for three years now but I don't understand
> how a person can be electrocuted by touching one part of the circuit in
> a mains supply.
>
> If I hold one lead of an ohmmeter in my left hand, and the other in my
> right hand, it registers the resistance to be approximately 2 megaohms,
> which is ridiculously high. Now if I hold one lead in my hand, and dig
> the other into the grass, it doesn't even register -- I may as well be
> holding the leads apart in thin air.
The resistance of the human body varies widely, depending on the nature
of the contact. Dry skin does measure around some megohmes, but sweaty
skin conducts much better, and if the contacts abrade or penetrate the
skin, the internal resistance can be as low as 300 ohms, hand to foot.
The effect of the current also varies with the path of the current
through the body, with paths that include the heart being the most
dangerous. For a brief shock, timing has some effect. A short zap at
just the wrong point in the heart cycle can cause the heart to "stumble"
into a fatal arhytmia.
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Author: Jon SlaughterDate: 12:56 03-04-08
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"Tomás Ó hÉilidhe" <toe@lavabit.com> wrote in message
news:97de30be-74bd-456b-96ca-ba2ce8b96024@b5g2000pri.googlegroups.com...
>
> I've been doing electronics for three years now but I don't understand
> how a person can be electrocuted by touching one part of the circuit
> in a mains supply.
>
> If I hold one lead of an ohmmeter in my left hand, and the other in my
> right hand, it registers the resistance to be approximately 2
> megaohms, which is ridiculously high.
> Now if I hold one lead in my hand, and dig the other into the grass,
> it doesn't even register -- I may as well be holding the leads apart
> in thin air.
>
> Current = Voltage divided by Resistance
>
> Current = 230 volts divided by 2 megaohms = 115 microamperes
>
> 115 microamperes is nowhere near enough to electrocute someone.
>
> So lets say I stick a metal rod into the socket on the wall. The
> current has to flow thru my hand, down to my foot, thru my cotton
> sock, thru my shoe, thru the wooden floorboards, thru the concrete,
> thru the clay down to the metal rod we call ground. Now excuse me, but
> is that not a RIDICULOUS amount of resistance, up in the gigohms
> somewhere?
>
> It may sound like I'm denying that people get electrocuted -- I'm not,
> I realise that people do get electrocuted. But I can't for the life of
> me understand how enough current can flow, given the massive
> resistances that are involved.
>
> Can anyone enlighten me?
Your not taking into account the blood stream. It offers a direct low
resistance path for current to get to the heart. All the current has to do
is break through the skin and not flow on it. If it flowed on it then you
wouldn't die even if it was 100A(although probably serious burns) because
your heart is not directly part of your skin.
Measure the resistance of your blood and then try measuring the resistance
between two points on your skin, first without pricking those points and
then pricking them. I bet you'll find a serious change in resistance.
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Author: =?ISO-8859-1?Q?Tom=E1s_=D3_h=C9ilidhe?=Date: 13:37 03-04-08
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John Popelish:
> Do the calculation again but with the other hand on the
> water tap or the grounded case of an appliance.
2 megaohms in series with less than an ohm = 2 megaohms
Still 115 microamperes.
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Author: Michael A. TerrellDate: 13:47 03-04-08
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Tomás Ó hÉilidhe wrote:
>
> John Popelish:
>
> > Do the calculation again but with the other hand on the
> > water tap or the grounded case of an appliance.
>
> 2 megaohms in series with less than an ohm = 2 megaohms
>
> Still 115 microamperes.
Then stick your hands into a live AC power line, after making sure
your will is up to date, and your insurance is paid up. You know just
enough to be dangerous. The resistance also depends on contact area,
and what part of the body. Loose the attitude, or someone will find you
dead from your ignorance.
--
aioe.org is home to cowards and terrorists
Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.
http://improve-usenet.org/index.html
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Author: =?ISO-8859-1?Q?Tom=E1s_=D3_h=C9ilidhe?=Date: 13:47 03-04-08
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Jon Slaughter:
> Measure the resistance of your blood and then try measuring the resistance
> between two points on your skin, first without pricking those points and
> then pricking them. I bet you'll find a serious change in resistance.
Scenario 1: I have intact skin on my hand, and intact skin on my foot.
I put an ohm meter across my hand and foot and measure 2 megaohms.
Scenario 2: I have an open bloody wound on my hand, and an open bloody
wound on my foot. I put an ohm meter across my hand and foot and
measure 300 ohms.
It's rare that you'll find someone with exposed blood on both their
hand and foot at the exact time that they're electrocuted. Without
even taking that into account tho, take out an ohm meter and measure
the resistance thru your sock. Then measure the resistance thru your
shoe. Then measure the resistance of a wooden floor board.
Really I just don't understand how 230 V is enough to drive current
thru me, thru my sock, thru my shoes, thru the floor boards, thru the
concrete, thru the clay, to ground.
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Author: =?ISO-8859-1?Q?Tom=E1s_=D3_h=C9ilidhe?=Date: 13:59 03-04-08
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Stephen J. Rush:
> The resistance of the human body varies widely, depending on the nature
> of the contact. Dry skin does measure around some megohmes, but sweaty
> skin conducts much better, and if the contacts abrade or penetrate the
> skin, the internal resistance can be as low as 300 ohms, hand to foot.
A lecturer in my college posed this argument to me before. He said
that if you stabbed the ohm meter into your foot and also into your
hand, then you'd measure a hell of a lot lower than 2 megohms.
People are often very nonchalant about this idea of "getting past the
skin", but it's not meager feat at all.
I'm taking about simply touching the positive terminal of an
electrical socket, not about slicing your hand open, then slicing your
foot open, then touching the socket.
And, even if the resistance from hand to foot was extremely low, even
in the region of something like 4 ohms, then that still doesn't
explain how the current flows from my foot, thru my sock, thru my
shoe. I bet if I put one terminal of an ohmmeter inside my shoe, and
the other on the sole of my shoe, that the resistance will be too high
to measure. (If I had an ohmmeter I'd do it right now).
I'd love to do an experiment with one of those corpses that gets
donated to scientific research. I had considered using a dead mouse,
like the ones you get from the petshop for feeding snakes, but they're
far too small. A dead pig might do the trick.
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Author: =?ISO-8859-1?Q?Tom=E1s_=D3_h=C9ilidhe?=Date: 14:12 03-04-08
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Michael A. Terrell:
> Then stick your hands into a live AC power line, after making sure
> your will is up to date, and your insurance is paid up. You know just
> enough to be dangerous. The resistance also depends on contact area,
> and what part of the body. Loose the attitude, or someone will find you
> dead from your ignorance.
If you'll read my original post, I explicitly express that I _don't_
deny that people get electrocuted, so your accusations of ignorance
and "attitude" are illformed. What I'm questioning is the science of
it, as we understand it today. I've never, ever, not once, heard a
single valid explanation of how someone can get electrocuted by
touching a 230 V mains terminal.
I'm no denying that it happens. In fact I'm acknowledge that it
happens, and I also acknowledge that I don't understand how it
happens, and so I'm inviting people here to discuss the science of it.
I myself know about DC, AC, resistivity, resistance, capacitance,
inductance, impedance... but none of these things explain how 230 V is
enough to kill me if I grab the positive terminal.
Here's the path of the current:
1) From my hand to my foot: About 2 megohms.
2) From my foot thru to the other side of my sock: Probably in the
megohms, if not gigaohms.
3) From my sock to the inside of my shoe, to the sole of my shoe:
Probably in the megohms, if not gigaohms.
I just can't understand how 230 V is enough to push anything other
than a negligible current thru that gargantuan resistance.
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Author: BerylDate: 15:20 03-04-08
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Tomás Ó hÉilidhe wrote:
> I've been doing electronics for three years now but I don't understand
> how a person can be electrocuted by touching one part of the circuit
> in a mains supply.
>
> If I hold one lead of an ohmmeter in my left hand, and the other in my
> right hand, it registers the resistance to be approximately 2
> megaohms, which is ridiculously high.
> Now if I hold one lead in my hand, and dig the other into the grass,
> it doesn't even register -- I may as well be holding the leads apart
> in thin air.
>
> Current = Voltage divided by Resistance
>
> Current = 230 volts divided by 2 megaohms = 115 microamperes
>
> 115 microamperes is nowhere near enough to electrocute someone.
>
> So lets say I stick a metal rod into the socket on the wall. The
> current has to flow thru my hand, down to my foot, thru my cotton
> sock, thru my shoe, thru the wooden floorboards, thru the concrete,
> thru the clay down to the metal rod we call ground. Now excuse me, but
> is that not a RIDICULOUS amount of resistance, up in the gigohms
> somewhere?
>
> It may sound like I'm denying that people get electrocuted -- I'm not,
> I realise that people do get electrocuted. But I can't for the life of
> me understand how enough current can flow, given the massive
> resistances that are involved.
>
> Can anyone enlighten me?
Not I. The supposed 230 volt force isn't merely 230 though, that's RMS.
Maybe the body is a capacitor, not just a resistor. And how much current
flows across firing synapses?
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Author: John O'FlahertyDate: 15:49 03-04-08
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On Thu, 3 Apr 2008 10:59:48 -0700 (PDT), Tomás Ó hÉilidhe
<toe@lavabit.com> wrote:
>Stephen J. Rush:
>
>> The resistance of the human body varies widely, depending on the nature
>> of the contact. Dry skin does measure around some megohmes, but sweaty
>> skin conducts much better, and if the contacts abrade or penetrate the
>> skin, the internal resistance can be as low as 300 ohms, hand to foot.
>
>A lecturer in my college posed this argument to me before. He said
>that if you stabbed the ohm meter into your foot and also into your
>hand, then you'd measure a hell of a lot lower than 2 megohms.
>
>People are often very nonchalant about this idea of "getting past the
>skin", but it's not meager feat at all.
>
>I'm taking about simply touching the positive terminal of an
>electrical socket, not about slicing your hand open, then slicing your
>foot open, then touching the socket.
>
>And, even if the resistance from hand to foot was extremely low, even
>in the region of something like 4 ohms, then that still doesn't
>explain how the current flows from my foot, thru my sock, thru my
>shoe. I bet if I put one terminal of an ohmmeter inside my shoe, and
>the other on the sole of my shoe, that the resistance will be too high
>to measure. (If I had an ohmmeter I'd do it right now).
>
>I'd love to do an experiment with one of those corpses that gets
>donated to scientific research. I had considered using a dead mouse,
>like the ones you get from the petshop for feeding snakes, but they're
>far too small. A dead pig might do the trick.
If you touch a live power wire, not touching anything else, standing
in dry shoes, you won't get shocked. If your shoes and socks are wet,
or even damp, and you are on a concrete floor, you could carry enough
current to make your heart fibrillate. Consider the great surface area
of feet compared to the contact area of an ohmmeter probe. If the feet
are 12 inches by 2.5 inches, for 50 square inches total, that is
50/(39.37^2) = .032 m^2, and if the ohmmeter probe is 1.5 cm by 2 mm,
or 3e-5 m^2, the feet will have 1000 times less resistance.
To experiment, you don't even need a dead pig - use the ohmmeter
while standing in damp socks on a metal plate, with the meter
connected to another metal plate for the hand contact.
--
John
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Author: Yukio YANODate: 16:09 03-04-08
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Beryl wrote:
> Tomás Ó hÉilidhe wrote:
>> I've been doing electronics for three years now but I don't understand
>> how a person can be electrocuted by touching one part of the circuit
>> in a mains supply.
>>
>
>>
>> It may sound like I'm denying that people get electrocuted -- I'm not,
>> I realise that people do get electrocuted. But I can't for the life of
>> me understand how enough current can flow, given the massive
>> resistances that are involved.
>>
>> Can anyone enlighten me?
>
Yes, its quite simple really, If you are like most people ,its "ouch
Shit its live !" But for a very few unlucky souls who might have wet
feet and or accidentally stepped on alive conductor, their friends will
say "hail mary". Any med-tech expects to find 50,000 OHMS or less,
between his electrodes ! In summary your resistance numbers are
optimistic to say the least, most people are very lucky, very few will
be found dead and I could electrocute someone in the middle of a desert
with only a nine volt transistor battery.
Yukio YANO
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Author: Jon SlaughterDate: 16:20 03-04-08
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"Tomás Ó hÉilidhe" <toe@lavabit.com> wrote in message
news:b4c018a9-f16c-4c6f-88c1-ce1856a28afb@s19g2000prg.googlegroups.com...
> Jon Slaughter:
>
>> Measure the resistance of your blood and then try measuring the
>> resistance
>> between two points on your skin, first without pricking those points and
>> then pricking them. I bet you'll find a serious change in resistance.
>
> Scenario 1: I have intact skin on my hand, and intact skin on my foot.
> I put an ohm meter across my hand and foot and measure 2 megaohms.
>
> Scenario 2: I have an open bloody wound on my hand, and an open bloody
> wound on my foot. I put an ohm meter across my hand and foot and
> measure 300 ohms.
>
> It's rare that you'll find someone with exposed blood on both their
> hand and foot at the exact time that they're electrocuted. Without
> even taking that into account tho, take out an ohm meter and measure
> the resistance thru your sock. Then measure the resistance thru your
> shoe. Then measure the resistance of a wooden floor board.
>
> Really I just don't understand how 230 V is enough to drive current
> thru me, thru my sock, thru my shoes, thru the floor boards, thru the
> concrete, thru the clay, to ground.
>
Um... your measuring the skin restance from your foot to your arm. Once the
electricity gets through your skin to your blood its much smaller. That is
the point. You think that the current must travel along the skin? The blood
is right below the skin.
Think of a wire with insulation. The insulation is your skin. The wire is
your blood. If you put a multimeter or low voltage on the insulation you
don't get squat. Your ohmmeter might read 100000MOhms or something... But
put a high enough voltage on it and it will get through the insulation to
the copper and it doesn't matter how long the wire is.
You are using a multimeter to test something and then assuming that the real
situation is like the multimeter.
If your multimeter uses 200V then its a much better test... Although your
still not taking into account other issues.
Who said it will drive current through you with all that stuff? Why do
people where protective equipment when working with HV? ITS NOT THAT IT
WILL!!! ITS THAT IT CAN!! THERES A BIG DIFFERENCE.
Do you want to take a chance of killing yourself when working with 10kV
because you accidently stepped in some wet dog poo and had nail through the
soul of your foot that was ever so slightly piercing your skin... and then
accidently stuck yourself with a HV wire? (In fac the nail doesn't even need
to pierce your skin at that voltage)
What you don't get is that accidents can happen. Chances are if you go grab
the two ends of the mains you will not get electrocuted(you probably will
get shocked)... but if you do that 100 times there is a much larger chance.
If you are cautious then you can reduce your chances significantly but that
chance always remains.
Do you realize that you can easily die from 500kV high power line just by
standing a few feet away? (In fact the chances are close to 1 that you will)
Whats the difference between 200V and 500kV? Not that much if your stupid
cause even 10V can kill. Ok, maybe not 10V as it depends on a lot of factors
but your chances of dieing go up dastically with voltage... although you can
mitagate to some degree that with a little common sense.
I think your problem is that you seem to believe because it won't kill you
in one circumstance that it will never kill you in any other circumstance.
(and you happen to be taking the best case scenario instead of the worse
case)
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Author: stanDate: 16:37 03-04-08
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John Popelish wrote:
> Tomás Ó hÉilidhe wrote:
>> I've been doing electronics for three years now but I don't understand
>> how a person can be electrocuted by touching one part of the circuit
>> in a mains supply.
>>
>> If I hold one lead of an ohmmeter in my left hand, and the other in my
>> right hand, it registers the resistance to be approximately 2
>> megaohms, which is ridiculously high.
>> Now if I hold one lead in my hand, and dig the other into the grass,
>> it doesn't even register -- I may as well be holding the leads apart
>> in thin air.
>>
>> Current = Voltage divided by Resistance
>>
>> Current = 230 volts divided by 2 megaohms = 115 microamperes
>>
>> 115 microamperes is nowhere near enough to electrocute someone.
>>
>> So lets say I stick a metal rod into the socket on the wall. The
>> current has to flow thru my hand, down to my foot, thru my cotton
>> sock, thru my shoe, thru the wooden floorboards, thru the concrete,
>> thru the clay down to the metal rod we call ground. Now excuse me, but
>> is that not a RIDICULOUS amount of resistance, up in the gigohms
>> somewhere?
>>
>> It may sound like I'm denying that people get electrocuted -- I'm not,
>> I realise that people do get electrocuted. But I can't for the life of
>> me understand how enough current can flow, given the massive
>> resistances that are involved.
>>
>> Can anyone enlighten me?
>
> Do the calculation again but with the other hand on the
> water tap or the grounded case of an appliance.
>
How much current do you think it takes o cause death? Do you think it
matters if it's AC or DC?
Your model calculations treat the human body as if it were essentially a
lump of carbon with electrodes attached. While a typical resister is
largely considered as a fairly linear device at a constant temperature
the human body is generally not a linear resistance.
The path as well as the quantity of current matters a great deal when
trying to predict the effect on the human body. A human heart basically
operates as an electromechanical device and with typically very low
current. It really doesn't take much current to interfere with a normal
heart beat. In fact with 60 HZ AC it's very easy to cause the heart to
start something called ventricular fibrillation which is a particularly
dangerous condition. The heart becomes basically unable to effectively
circulate blood and that is a Bad Thing(TM).
The truth is that it's very complicated to determine an accurate
resistance that a human body will present to a difference in potential.
A simple multimeter will not give you a meaningful measure. The probes
and their point of contact will have a very large impact on your
multimeter reading. Not to mention with a nonlinear resistance like a
human body there's a difference between say a 9V DC multimeter and 115V
AC. Of couurse if you built a 115V AC multimeter you'd probably get a
very different reading even using the same ineficient probes from your
standard multimeter.
There are a lot of variables involved and it's not likely you will get a
meaningful resistance from a multimeter. I also think you would be
surprised how little current it can take to upset a normal heart rhythm
and cause reduced or complete loss of normal blood circulation.
There are also other impacts from current flowing through the body. It
can easily disturb the ions in the blood and cells die quickly when
required ions aren't present is correct quantity. Cells count on some
ons for proper hydration and it's not hard to over/under hydrate to the
point of permanent damage. While some cells can divide and replace the
damaged cells, the process isn't instantaneous.
Electrocution is complicated. Consider that some people survive being
hit by lightening and some die from simple contact with a wall outlet.
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Author: David L. JonesDate: 17:08 03-04-08
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On Apr 4, 3:05 am, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> I've been doing electronics for three years now but I don't understand
> how a person can be electrocuted by touching one part of the circuit
> in a mains supply.
>
> If I hold one lead of an ohmmeter in my left hand, and the other in my
> right hand, it registers the resistance to be approximately 2
> megaohms, which is ridiculously high.
> Now if I hold one lead in my hand, and dig the other into the grass,
> it doesn't even register -- I may as well be holding the leads apart
> in thin air.
>
> Current =3D Voltage divided by Resistance
>
> Current =3D 230 volts divided by 2 megaohms =3D 115 microamperes
>
> 115 microamperes is nowhere near enough to electrocute someone.
>
> So lets say I stick a metal rod into the socket on the wall. The
> current has to flow thru my hand, down to my foot, thru my cotton
> sock, thru my shoe, thru the wooden floorboards, thru the concrete,
> thru the clay down to the metal rod we call ground. Now excuse me, but
> is that not a RIDICULOUS amount of resistance, up in the gigohms
> somewhere?
Not at several hundred volts.
> It may sound like I'm denying that people get electrocuted -- I'm not,
> I realise that people do get electrocuted. But I can't for the life of
> me understand how enough current can flow, given the massive
> resistances that are involved.
>
> Can anyone enlighten me?
As others have said, the body (and your clothing and footwear etc) and
the path taken is not just a simple resistor model, it is a very
complex model with dynamic impedance that changes with voltage. A
simple multimeter which tests at say 1V DC is not representative. If
you tried it with a "megger" resistance meter (and you shouldn't, it's
DANGEROUS!) at a few hundreds volts and it'll be a different story.
Take into account capacitive issues and it's a different story again.
And the list goes on.
Even a simplistic model is very difficult to construct.
Dave.
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Author: John FieldsDate: 17:12 03-04-08
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On Thu, 3 Apr 2008 09:05:36 -0700 (PDT), Tomás Ó hÉilidhe
<toe@lavabit.com> wrote:
>
>I've been doing electronics for three years now but I don't understand
>how a person can be electrocuted by touching one part of the circuit
>in a mains supply.
---
If another part of their body isn't somehow connected to the other
side of the mains supply, they can't.
---
>If I hold one lead of an ohmmeter in my left hand, and the other in my
>right hand, it registers the resistance to be approximately 2
>megaohms, which is ridiculously high.
---
Why? It's what it is.
---
>Now if I hold one lead in my hand, and dig the other into the grass,
>it doesn't even register -- I may as well be holding the leads apart
>in thin air.
>
>Current = Voltage divided by Resistance
>
>Current = 230 volts divided by 2 megaohms = 115 microamperes
>
>115 microamperes is nowhere near enough to electrocute someone.
>
>So lets say I stick a metal rod into the socket on the wall. The
>current has to flow thru my hand, down to my foot, thru my cotton
>sock, thru my shoe, thru the wooden floorboards, thru the concrete,
>thru the clay down to the metal rod we call ground. Now excuse me, but
>is that not a RIDICULOUS amount of resistance, up in the gigohms
>somewhere?
---
You seem to be missing the point, which is that for electrocution to
occur, sufficient charge has to flow through your body to kill you.
The path you describe will exhibit a high resistance, so you'll be
safe as long as you only touch the one mains terminal.
JF
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Author: John PopelishDate: 18:40 03-04-08
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Tom=E1s =D3 h=C9ilidhe wrote:
> John Popelish:
>=20
>> Do the calculation again but with the other hand on the
>> water tap or the grounded case of an appliance.
>=20
> 2 megaohms in series with less than an ohm =3D 2 megaohms
>=20
> Still 115 microamperes.
But skin resistance is not linear with respect to voltage.=20
somewhere around 50 volts, the resistance begins to drop,=20
dramatically. Expect to have your teeth jarred loose with=20
120 volts hand to hand, even if your heart does not=20
fibrillate. I have done it, accidentally, and I didn't like=20
it at all.
--=20
Regards,
John Popelish
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Author: John PopelishDate: 19:00 03-04-08
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Tom=E1s =D3 h=C9ilidhe wrote:
> Here's the path of the current:
> 1) From my hand to my foot: About 2 megohms.
> 2) From my foot thru to the other side of my sock: Probably in the
> megohms, if not gigaohms.
> 3) From my sock to the inside of my shoe, to the sole of my shoe:
> Probably in the megohms, if not gigaohms.
>=20
> I just can't understand how 230 V is enough to push anything other
> than a negligible current thru that gargantuan resistance.
And it almost certainly does not pass much current through=20
that path. That is not the path that electrocutes people.=20
Above a hundred volts, skin to skin resistance is in the=20
hundreds or low thousands of ohms. People get electrocuted=20
by touching line voltage with bare skin, and touching=20
grounded conductive surfaces or liquids with some other part=20
of their skin. But not through rubber soled shoes.
--=20
Regards,
John Popelish
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Author: David L. JonesDate: 20:07 03-04-08
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On Apr 4, 5:12 am, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> Michael A. Terrell:
>
> > Then stick your hands into a live AC power line, after making sure
> > your will is up to date, and your insurance is paid up. You know just
> > enough to be dangerous. The resistance also depends on contact area,
> > and what part of the body. Loose the attitude, or someone will find you=
> > dead from your ignorance.
>
> If you'll read my original post, I explicitly express that I _don't_
> deny that people get electrocuted, so your accusations of ignorance
> and "attitude" are illformed. What I'm questioning is the science of
> it, as we understand it today. I've never, ever, not once, heard a
> single valid explanation of how someone can get electrocuted by
> touching a 230 V mains terminal.
>
> I'm no denying that it happens. In fact I'm acknowledge that it
> happens, and I also acknowledge that I don't understand how it
> happens, and so I'm inviting people here to discuss the science of it.
>
> I myself know about DC, AC, resistivity, resistance, capacitance,
> inductance, impedance... but none of these things explain how 230 V is
> enough to kill me if I grab the positive terminal.
>
> Here's the path of the current:
> 1) From my hand to my foot: About 2 megohms.
On your multimeter at 1V. It will vary a LOT under all sorts of
conditions.
That has very little correlation to the "resistance" at much higher
voltages.
> 2) From my foot thru to the other side of my sock: Probably in the
> megohms, if not gigaohms.
Same as above.
> 3) From my sock to the inside of my shoe, to the sole of my shoe:
> Probably in the megohms, if not gigaohms.
Same as above.
> I just can't understand how 230 V is enough to push anything other
> than a negligible current thru that gargantuan resistance.
You just don't get it.
The "resistance" varies a LOT based on all sorts of factors, not least
of which is voltage.
The figures you have measured on your multimeter are of very little
indication at all.
That is why "high voltage" resistance meters ("meggers") are
available
and commonly used to test insulation resistance at mains voltages.
Dave.
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Author: John FieldsDate: 20:35 03-04-08
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On Thu, 3 Apr 2008 09:05:36 -0700 (PDT), Tomás Ó hÉilidhe
<toe@lavabit.com> wrote:
>I've been doing electronics for three years now but I don't understand
>how a person can be electrocuted by touching one part of the circuit
>in a mains supply.
---
Perhaps, then, an alternate career path where all you have to do is
parrot: "D'ya want fries with that?" might be more appropriate.
Sorry, I couldn't resist. ;)
JF
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