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FrogDawg

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I am mainly wondering if and why the assumption below is wrong.

So I have searched around and there seems to be a consensus that 100ma to 200ma is enough current to be lethal. Grabbing the leads on my Fluke I get a resistance reading most of the time between 1M ohm and 2M ohm. So to get say 100ma of current wouldn't it take V=IR or .100A x 1,000,000 ohms which is 100,000 volts to deliver the required current to be lethal in these circumstances?

I know that the resistance varies quite a bit from location and if my hands are wet, etc. but I just want to know if the above assumption is wrong and why? It seems like it has to be wrong because 100,000 volts is a lot and it seems that 120v household current could be lethal right? Using 120v however, would only be I=V/R or .12ma which some sources say I wouldn't even feel. I'm by no means going to test this. I just want to know.

Some sources have stated a different number for the lethality of current when working with AC vs DC. Even in these cases however it seems like it would take a lot of voltage to get a lethal shock through my hands on an average day.

I have been shocked when working on household wiring when I thought the breaker was off and it wasn't and I can assure you I felt it.

Dennis Alwon

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A gfci breaker responds when there is a leakage of current between 4 to 6 ma. Apparently it becomes more dangerous as the ma increase. At what point someone dies is dependent on a few factors so it is not the same for everyone.

Voltage will shock you but it won't kill you until you get up there in volts while it doesn't take much amps to do you in.

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Wardenclyffe

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120 volts isn't “strong” enough to push much current through your body which is why most 120 volt shocks are survivable. However, it's still enough current to interfere with your nerves' communication so if your heart happens to be part of this “current highway” it may start beating erratically, which can cause death.

gpop

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You are forgetting time and path.
As time increases you start to cook and as you are basically made from carbon your body resistance will drop until you are a crispy critter. 120v may not have enough force to kill you but it can make your muscles contract so you are unable to let go then it can take its time to slowly cook you.

100,000v at 100ma will remove what ever part of the body touched it. It will also cause ever muscle to contract with enough force to break your own bones while cooking you from the inside out.

Felling brave or stupid pull the cap of a lawn mower spark plug as that's somewhere in the 15-25 kv range and around 1ma. (they call 1 ma the perception level.....well i perceive that it hurts like hell)

Easy

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Tasers put out between 20,000 and 150,000 volts. The standard police issue is about 50,000 volts but it’s not the voltage alone that will kill you. From what I have read the lowest recorded voltage that caused death is 42 volts. Time is also a factor and 0.1 ampere for 2 seconds can be fatal.

just the cowboy

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The other thing is your meter is very low voltage so it don’t get thru the skin as easy. If you did the same test with a megger the resistance (don’t) you will get a different teading

Signal1

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OP, I hope you don't have some kind of , plan.

There are people you can talk to............

FrogDawg

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OP, I hope you don't have some kind of , plan.

There are people you can talk to............
I appreciate the concern, Nothing sinister here. It's just that once a question forms in my mind it is hard to focus on anything else until I get a satisfactory answer. I have found some interesting info that I will post but I don't have it put together at the moment.

I thought it was clear but I'll mention it anyway. There is no need for "it's not the voltage that kills you it's the amps" comments. I already mentioned that the consensus is 100ma - 200ma is lethal. However, it takes a certain voltage to move a certain amount of current over a certain resistance. That is why the voltage level is important here. We already know the lethal current of 100ma and if my Fluke is correct we know the resistance. So depending on the voltage a certain amount of current will flow.

For instance, if I touch the terminals of a 12v car battery no current flows through me, right? Wrong. It's just such a small amount that it does not hurt you and you can't perceive it happening. Assuming the same resistance values as before and 12.8v there would be around .0128ma of current. If your hands were soaking wet you would have less resistance and more current would flow.

The post title is about voltage because we know the current limit and the resistance. So we can control the amount of current flow based on the voltage. It seems inductance has a large part to play in this and so while my examples were about DC we can just assume we're talking AC to factor out inductance.

Really, I guess the question is not really even about how much voltage is required it's about whether there is something wrong with the calculations or assumptions.

Anyway, I appreciate all the answers to a question that really doesn't matter at all except to appease my curiousity.

gpop

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Tasers put out between 20,000 and 150,000 volts. The standard police issue is about 50,000 volts but it’s not the voltage alone that will kill you. From what I have read the lowest recorded voltage that caused death is 42 volts. Time is also a factor and 0.1 ampere for 2 seconds can be fatal.

If i remember correctly tasers are 2 stage. The first stage uses a cap to get the persons attention at a higher voltage then drops to a safer lower voltage.

just the cowboy

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For instance, if I touch the terminals of a 12v car battery no current flows through me, right? Wrong. It's just such a small amount that it does not hurt you and you can't perceive it happening. Assuming the same resistance values as before and 12.8v there would be around .0128ma of current. If your hands were soaking wet you would have less resistance and more current would flow.
Puncture your skin with two leads hooked to a car battery and tell me you won't get a shock.

gpop

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I appreciate the concern, Nothing sinister here. It's just that once a question forms in my mind it is hard to focus on anything else until I get a satisfactory answer. I have found some interesting info that I will post but I don't have it put together at the moment.

I thought it was clear but I'll mention it anyway. There is no need for "it's not the voltage that kills you it's the amps" comments. I already mentioned that the consensus is 100ma - 200ma is lethal. However, it takes a certain voltage to move a certain amount of current over a certain resistance. That is why the voltage level is important here. We already know the lethal current of 100ma and if my Fluke is correct we know the resistance. So depending on the voltage a certain amount of current will flow.

For instance, if I touch the terminals of a 12v car battery no current flows through me, right? Wrong. It's just such a small amount that it does not hurt you and you can't perceive it happening. Assuming the same resistance values as before and 12.8v there would be around .0128ma of current. If your hands were soaking wet you would have less resistance and more current would flow.

The post title is about voltage because we know the current limit and the resistance. So we can control the amount of current flow based on the voltage. It seems inductance has a large part to play in this and so while my examples were about DC we can just assume we're talking AC to factor out inductance.

Really, I guess the question is not really even about how much voltage is required it's about whether there is something wrong with the calculations or assumptions.

Anyway, I appreciate all the answers to a question that really doesn't matter at all except to appease my curiousity.
Its a interesting question and this website explain how the skin acts as a insulator up to around 500v (you skin is like a MOV where its high resistance until you pass 500v then its just a dead short). Your gummy bits inside are only good for 300 ohms of resistance.

gpop

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Puncture your skin with two leads hooked to a car battery and tell me you won't get a shock.
that some kinda of 50 shades of grey thing?

FrogDawg

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Puncture your skin with two leads hooked to a car battery and tell me you won't get a shock.
Who said anything about punctured skin? The resistance was already stated but let's say you did. I haven't tested my punctured self but have seen 400 ohms used as the resistance for that scenario. That would be 12.8v / 400 ohms which would be 32ma. From what I have read that would hurt like hell. I don't know about that 400 ohms though. I did see a guy testing resistance with a raw pork chop on youtube but I can't remember the value he got.

just the cowboy

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Who said anything about punctured skin? The resistance was already stated but let's say you did. I haven't tested my punctured self but have seen 400 ohms used as the resistance for that scenario. That would be 12.8v / 400 ohms which would be 32ma. From what I have read that would hurt like hell. I don't know about that 400 ohms though. I did see a guy testing resistance with a raw pork chop on youtube but I can't remember the value he got.
You stated it with a resistance from your meter, that is not a true reading, it depends on what voltage output you tested at.

emtnut

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which is 100,000 volts to deliver the required current to be lethal in these circumstances?
If they could speak, there are a LOT of dead people that would disagree.

120V dangerous, usually a shock, can kill under the right circumstances
240V you tend to stick to it.
480-600V you're in hospital IF you're lucky
above that, chances of survival is slim at best.

For the record, you don't need anywhere near 100mA to be lethal.

FrogDawg

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You stated it with a resistance from your meter, that is not a true reading, it depends on what voltage output you tested at.
I didn’t say anything about punctured skin. The question was not about punctured skin. It was very specific. A meter wouldn’t be much good if it didn’t accurately measure resistance. It seems off topic to go into how a multimeter measures resistance so I won’t.

FrogDawg

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For the record, you don't need anywhere near 100mA to be lethal.
What are your sources? I’m interested. I find the 100ma - 200ma number to be quoted often.

paulengr

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I am mainly wondering if and why the assumption below is wrong.

So I have searched around and there seems to be a consensus that 100ma to 200ma is enough current to be lethal. Grabbing the leads on my Fluke I get a resistance reading most of the time between 1M ohm and 2M ohm. So to get say 100ma of current wouldn't it take V=IR or .100A x 1,000,000 ohms which is 100,000 volts to deliver the required current to be lethal in these circumstances?

I know that the resistance varies quite a bit from location and if my hands are wet, etc. but I just want to know if the above assumption is wrong and why? It seems like it has to be wrong because 100,000 volts is a lot and it seems that 120v household current could be lethal right? Using 120v however, would only be I=V/R or .12ma which some sources say I wouldn't even feel. I'm by no means going to test this. I just want to know.

Some sources have stated a different number for the lethality of current when working with AC vs DC. Even in these cases however it seems like it would take a lot of voltage to get a lethal shock through my hands on an average day.

I have been shocked when working on household wiring when I thought the breaker was off and it wasn't and I can assure you I felt it.
It also varies with frequency. Curiously enough the worst skin resistance is at around 50-70 Hz. It also goes down somewhat with applied voltage. And there is a time factor. Under about 8 ms and fibrillation will not occur. Over 5 sec and if it hadn’t been triggered it won’t happen. It’s also strangely body weight dependent, even among species. So a lot of the testing was done with rabbits and dogs knowing that.

So at 0.1 A (100 mA) with roughly 1 kilo-ohm resistance through the body (yes dry skin makes a difference) you get 1000x0.1 = 100 VAC. There is no real limit with DC…it just breaks bones. And the sensation threshold is at 1 mA, “shocked” feeling above that, somewhat lower for women than men. So GFCIs are set to 3-5 mA based on the idea that’s when you feel it.

So soak your hands and try again.

FrogDawg

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There is no real limit with DC…it just breaks bones.
What do you mean by this?
So soak your hands and try again.
Again the question is about the amount of voltage needed to move a certain amount of current over an already specified resistance. I don't need to soak my hands or puncture my skin. That would give me a different resistance and is not the question. I don't want to know how different resistances or amounts of current affect me. The question is how different voltages affect the amount of current I would receive with my specified resistance. Actually, I already know how they should affect me the question was about the mathematical assumptions made.

It seems the biggest factor I overlooked is how the capacitance of the body blocks to an extent DC current.

FrogDawg

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Its a interesting question and this website explain how the skin acts as a insulator up to around 500v (you skin is like a MOV where its high resistance until you pass 500v then its just a dead short). Your gummy bits inside are only good for 300 ohms of resistance.

This was a fantastic find, particularly the underlying paper on the breakdown of resistance.