Volts vs Amps

Carultch

Senior Member
Location
Massachusetts
It's not the fall that kills ya'; it's the sudden stop at the bottom. :D

That sure is true. The fall imposes zero stress on the body, while the sudden stop imposes hundreds, if not thousands of times as much stress on the body as it ordinarily experiences.

Although astronauts in orbit are subject to a condition that feels like perpetual falling. Even though this is an absence of stress on the body, it still causes significantly more deterioration of the skeleton and muscles than we experience on Earth. It is called disuse atrophy, due to the way that bones and muscles are made for rebuilding themselves from regular wear and tear. So if the "fall" is prolonged, much longer than it could last on Earth, it can do some serious damage.

Have any microgravity experiments shown that the fall literally could kill you, from atrophy?
 

Carultch

Senior Member
Location
Massachusetts
Not quite. The Roman Catholic Church has a panel of linguists whose duty is to create new Latin words to keep up with modern needs. The grammar does remain uncanged AFAIK.
So Latin may not be nearly as dead of a language as everyone says it is. I think we'll need a better example.

Cuneiform is a dead language
As dead as it can be
It killed off all the Sumerians
And now it is killing me
 

MD84

Senior Member
Location
Stow, Ohio, USA
This was a very interesting conversation. I hope the OP found it useful. I think the missing link to understanding is resistance. Ohms law does not make sense without resistance just as an understanding of volts vs amps does not make sense without resistance.

As it was already explained the reason the 6v battery is more hazardous is the internal resistance. The larger capacity 6v battery has lower resistance than the 9v battery.

I started reading this thread thinking current kills. Now after reading it I agree that it is the relationship of voltage, current, and resistance that can kill. It is useful to describe the amount of current that can kill a human. It does however require a voltage to force that current to flow. The voltage and resistance will determine how much current will flow.

Typically 6v or 9v does not have the pressure to push through our skin. If the resistance of the skin was compromised it could very well cause enough current to kill. I believe OSHA sets the limit at 50 volts. Perhaps this level of voltage is beginning to have enough pressure to push through skin. At 240v and greater skin is likely to be easily penetrated.

When sizing protective grounds one takes the available fault current and resistance of the ground assembly to determine what voltage will drop across the equipment should it become energized. This is called the voltage across the man. It is typically limited to 75 or 100 volts. 75v for longer clearing times like on distribution or transmission lines and 100 volts for shorter clearing times like in substations or feeders. This is because the the maximum safe current through the body can be higher when the exposure time is shorter.

So I would say it is not only amps that kills you. You can be killed depending on the resistance of your body which is placed across a difference of potential for a length of time in which sufficient current flows through vital organs.
 

Carultch

Senior Member
Location
Massachusetts
This was a very interesting conversation. I hope the OP found it useful. I think the missing link to understanding is resistance.
I agree, it is very interesting as well.

Ohms law does not make sense without resistance just as an understanding of volts vs amps does not make sense without resistance.
Believe it or not, the equation that we ordinarily think of as Ohm's law, isn't really Ohm's law the way that Georg Ohm developed the law.

V=I*R is really a transposed formula of the definition of resistance.

Ohm's law is that resistance is a property of the material, that is independent of I and V. Instead, resistance is a function of geometry, temperature and the material's electrical properties.

If Ohm's law weren't typically true in most simple examples, the concept of resistance and a formula such as V=I*R wouldn't be very useful. So it makes complete sense that V=I*R is taught as Ohm's law. In the water analogy that we all use as an introduction to the concept, the relationship between flow rate and pressure difference is extremely non-linear. As a result, the concept of hydraulic resistance is usually abandoned in fluids engineering, for formulas that more closely match the way to keep track of experimental results.

As it was already explained the reason the 6v battery is more hazardous is the internal resistance. The larger capacity 6v battery has lower resistance than the 9v battery.
I never thought of it this way. In this example, I suppose it really is the terminal operating voltage of the battery that matters, for directly determining the amps through your body.

So I would say it is not only amps that kills you. You can be killed depending on the resistance of your body which is placed across a difference of potential for a length of time in which sufficient current flows through vital organs.
Well, damage to a standard Ohmic resistor is due to the Watt rating being exceeded, and the component overheating. So I would expect that Watts would matter most.

A human body is a lot more complex than a simple Ohmic resistor. A human body will obey Ohm's law in most situations that are relatively safe, and current alone is probably an accurate enough metric of danger in the safe regime. But comparing it to situations that are fatal or permanently damaging, I would not expect the body to have the same Ohmic resistance it has in a safe situation of shock, and I would expect that the damage to the skin would exacerbate the problem by reducing the body's resistance to much less.
 
That's not the issue, and you are correct in that sense, of course. But it's not the effects of the voltage or the power that causes damage. It's the effects of current.

If 150 mA is fatal through a path, is the voltage going to change that? No. Will voltage be required to reach that level? Yes, but depending on the path, the voltage needed can vary from almost 0* to tens of thousands of volts. If only 5 mA passes through the same path, no matter how much voltage it takes, even tens of thousands, that 5 mA will be nearly harmless.

Yes, voltage is always present in an injury or fatality but it's not responsible for it.

*That's a hazard of IV's. It takes very little voltage through an IV in a person to cause harmful current levels.
So is 150 mA fatal regardless of the voltage? even if the voltage was tinny tiny?
/
 
Another guy says that an amp is a fixed amount of energy called a coolam, I think.
So if that was true than that would mean that if you had small voltage than you would need a lot of it to make one amp. It would further mean that not only could an amp not harm you with out some voltage. But all the people who say that it is the amps that kill you are completely wrong.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
Another guy says that an amp is a fixed amount of energy called a coolam, I think.
So if that was true than that would mean that if you had small voltage than you would need a lot of it to make one amp. It would further mean that not only could an amp not harm you with out some voltage. But all the people who say that it is the amps that kill you are completely wrong.
Go back and read post #75.
 

Carultch

Senior Member
Location
Massachusetts
Another guy says that an amp is a fixed amount of energy called a coolam, I think.
So if that was true than that would mean that if you had small voltage than you would need a lot of it to make one amp. It would further mean that not only could an amp not harm you with out some voltage. But all the people who say that it is the amps that kill you are completely wrong.
The unit name you are looking for is Coulomb.

A Coulomb is the unit of charge. Not energy, but electrical charge. An enormous number of either protons (+) or electrons (-). There are 6.24 Quintillion protons in 1 Coulomb worth of charge.

A flow rate of 1 Coulomb per second is what we define as an Ampere.

It isn't that an ampere could "not harm you without voltage", but rather that an ampere couldn't flow through you, without enough voltage difference across you causing it to flow.
 

kwired

Electron manager
Location
NE Nebraska
A human body is a lot more complex than a simple Ohmic resistor. A human body will obey Ohm's law in most situations that are relatively safe, and current alone is probably an accurate enough metric of danger in the safe regime. But comparing it to situations that are fatal or permanently damaging, I would not expect the body to have the same Ohmic resistance it has in a safe situation of shock, and I would expect that the damage to the skin would exacerbate the problem by reducing the body's resistance to much less.
I agree. the amount of current that flows will depend on circuit resistance and applied voltage - the human body is just a resistance inserted into the circuit during the event. Body tissues are damaged - some need more then the few milliamps that can kill you to see much damage, time of exposure also impacts how much damage there is. Certain types of tissue - in particular parts of the neuro-system may be what is most sensitive and only a few milliamps at any voltage level maybe causes damage. Kind of like overloading a conductor can damage the conductor.

Damage the nerves that get the signal from the brain to tell the heart to beat, it stops beating.

So is 150 mA fatal regardless of the voltage? even if the voltage was tinny tiny?
/
Where the current flows/what organs or tissue are damaged is what determines if the event was fatal. 100 amps that only travels through an an extremity like a hand doesn't directly effect vital organs, but that hand does have an injury, primarily burn injury, but could be cooked from inside out unlike many other burns.
 

Strathead

Senior Member
Quoted from "Person One": "The sky is blue."
Quoted from "Person Two": "No, you are wrong. The grass is green."

For my part, I will continue to think of the phenomenon of electrocution in the following way:

  • It is the flow of current through the body that causes damage to cells (e.g., muscle or nerve cells) and that interferes with the function of internal organs (e.g., the heart).
  • It is a difference in potential (i.e., the voltage source) that forces current to flow through the body in opposition to the resistance of human tissue. This is where Ohm's Law comes into play.
  • The rate at which energy (in units of "joules per second," commonly known as watts) is dissipated within the body can be determined by multiplying the voltage (in units of "joules per coulomb," commonly known as volts) times the current (in units of "coulombs per second," commonly known as amps). This is a simple consequence of the definition of "power."
  • If any two of these parameters (i.e., watts, volts, and amps) are present, the third will be present as well.
And this is a very good summary with one very minor caveat if you want to nitpick and that is that the resistance you refer to has more factors that "human tissue" but I only point that out because some people here will revert back to your first two sentences. It still, nonetheless is easily boiled down to a simplified statement that "amperage kills". The fact that you can't have amperage without voltage is a non-sequitur, because you can have infinite voltage without ample amperage all day long and the person won't die. And that is exactly what you imply above. I really find it hard to believe the iWire wants to argue this. I think it is both fundamental and important for new electricians to know right along with the "path through the heart" issue.
 

MD84

Senior Member
Location
Stow, Ohio, USA
you can have infinite voltage without ample amperage all day long and the person won't die
I disagree with this. Are you implying the bird on the wire analogy? The bird on the wire does not see the voltage potential between the phase conductors or ground. If the bird did see this voltage he would likely die. If infinite voltage were applied to a person then ample amperage would flow. A voltage exists between two points not one.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
So is 150 mA fatal regardless of the voltage? even if the voltage was tinny tiny?
/
The thing is, you cannot have 150mA current flowing from one hand to the other (through the heart) if the voltage difference between hands is "tinny tiny". Voltage and current are inextricably interconnected. Ohm's Law.

A car battery has hundreds of amps of current capacity, but if you put one hand on the positive terminal and the other on the negative it will not kill you. The current that flows through your body as a result of a 12V hand to hand voltage differential is far too low.
 

kwired

Electron manager
Location
NE Nebraska
The thing is, you cannot have 150mA current flowing from one hand to the other (through the heart) if the voltage difference between hands is "tinny tiny". Voltage and current are inextricably interconnected. Ohm's Law.

A car battery has hundreds of amps of current capacity, but if you put one hand on the positive terminal and the other on the negative it will not kill you. The current that flows through your body as a result of a 12V hand to hand voltage differential is far too low.
And on the flip side, electric fence chargers used for livestock containment operate at thousands of volts, but have such a high impedance the output current isn't fatal in general.
 

MD84

Senior Member
Location
Stow, Ohio, USA
One also needs to take into consideration that the human bodies resistance can change. If a cut or puncture is present this will allow a lower resistance path. If a voltage is present that us capable of pushing through the skin, once that pathway is created the resistance will drop and current will increase.
 

Strathead

Senior Member
So is 150 mA fatal regardless of the voltage? even if the voltage was tinny tiny?
/
THIS is why I insist on continuing with my premise. The answer is a qualified yes. As little as 100ma has been fatal with the right set of circumstances. One of those circumstances is the in and out points on the body that caused the current to flow through the heart. It is also likely the person had other health problems. So 100-150 ma isn't always fatal, but it can be fatal.

Either way, 150ma can be fatal. The thing that iWire falls back on is that the amount is directly proportional to voltage and inversely proportional to resistance. (if you don't understand this, please ask, and many here will explain deeper). So that means that a tiny voltage isn't likely to produce an amperage of 150ma across the heart.
 

Strathead

Senior Member
I disagree with this. Are you implying the bird on the wire analogy? The bird on the wire does not see the voltage potential between the phase conductors or ground. If the bird did see this voltage he would likely die. If infinite voltage were applied to a person then ample amperage would flow. A voltage exists between two points not one.
No, a better analogy to what I am referring to is a door knob in the winter. Infinite voltage is obviously (to me) a hypothetical theory, and it is likely that whatever stored to potential for a reaaaaaaaaaaaaaaalllllllllllyyyyyyyyyyy high voltage would also store enough energy for enough amperage flow to reach the 100ma threshold, but in theory, it doesn't have to. I read once that it takes approximately 12,000 volts to travel 1 inch. So a door know shocking you from 1/4 inch away probably hit you with 3,000 volts. Another example, but less so because there may actually be enough energy here, is the coil on an older care that puts out 12,000 volts. And it hurts, but generally doesn't have enough amperage to kill you.
 

Strathead

Senior Member
The thing is, you cannot have 150mA current flowing from one hand to the other (through the heart) if the voltage difference between hands is "tinny tiny". Voltage and current are inextricably interconnected. Ohm's Law.

A car battery has hundreds of amps of current capacity, but if you put one hand on the positive terminal and the other on the negative it will not kill you. The current that flows through your body as a result of a 12V hand to hand voltage differential is far too low.
I am not sure of exact resistances and teeny tiny (sorry I had to correct the spelling) is not a quantitative amount. Theoretically one could run in to a couple of needle thin electrodes right in the chest and if they didn't kill you they could induce current flow across across the heart with a pretty tiny voltage.

Silly I know, but then again, so is the entire premise of voltage. I don't know why someone hasn't stepped up and insisted that conductance is required, as it is every bit as important as voltage, but still neither of those is what stops a person heart.
 

MD84

Senior Member
Location
Stow, Ohio, USA
No, a better analogy to what I am referring to is a door knob in the winter. Infinite voltage is obviously (to me) a hypothetical theory, and it is likely that whatever stored to potential for a reaaaaaaaaaaaaaaalllllllllllyyyyyyyyyyy high voltage would also store enough energy for enough amperage flow to reach the 100ma threshold, but in theory, it doesn't have to. I read once that it takes approximately 12,000 volts to travel 1 inch. So a door know shocking you from 1/4 inch away probably hit you with 3,000 volts. Another example, but less so because there may actually be enough energy here, is the coil on an older care that puts out 12,000 volts. And it hurts, but generally doesn't have enough amperage to kill you.
A static charge cannot maintain voltage all day. What hypothetical infinite voltage source that does not maintain ample current lasts all day?

I am not sure of exact resistances and teeny tiny (sorry I had to correct the spelling) is not a quantitative amount. Theoretically one could run in to a couple of needle thin electrodes right in the chest and if they didn't kill you they could induce current flow across across the heart with a pretty tiny voltage.

Silly I know, but then again, so is the entire premise of voltage. I don't know why someone hasn't stepped up and insisted that conductance is required, as it is every bit as important as voltage, but still neither of those is what stops a person heart.
Resistance has been brought up. Isn't that the same thing here. Low resistance is the same as high conductance.
 
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