60Hz vs. 50Hz.

[Concillian]

Originally posted by: jagec
Newsflash: The nice thing about ANY constant frequency is that it can be used to synch clocks.

It became very apparent to me that most alarm clocks sync with the AC current when my brother moved to Italy and his clock advanced precisely 50 minutes every hour.

 

[DrPizza]

Originally posted by: Bassyhead

Originally posted by: bobsmith1492
240 volts is also much more dangerous, however, which is a good reason to use it for the majority of houshold appliances. It's a lot tougher to kill yourself on accident with 120 volts than 240, not to mention arcing, insulation and fire issues.

Whether you're electrocuted by 120 or 240 I don't think matters at those voltages. The circumstances of how you're electrocuted is going to be a greater factor (were you grounded, where the current takes a path through your body, etc). Also it's the current that kills, not voltage otherwise static electricity, sometimes in the hundreds of thousands or millions of volts, would kill frequently.

Hmm...
From hand to hand (through the body near the heart) resistance for a human is between 1000ohms and 2000 ohms. Using V=IR, this results in currents from .06 amps to .12 amps for 120 volts and from .12 amps to .24 amps for 240 volts.
.06 is around the limit that adults can tolerate before going into ventricular fibrillation... it's like the difference between being shot with an 8mm bullet through the heart or a 9mm bullet through the heart. It doesn't really matter.

2 ways to die: with prolonged contact, currents above 18 milliamps will cause the diaphragm to contract - victim suffocates. (Most adults cannot let go of a wire at about 15 milliamps (.015 amps). So, it only takes one tenth the current from 120 volts going from hand to hand to kill a person.

Now, the other way to die: the 60 Hz frequency is close to the heart's electrical signal - it can interfere with that signal and cause the heart to go into fibrillation. Death follows.

However, at higher frequencies, the body can withstand as much as 10 times as much current - so it isn't really the current that kills. Likewise, a 12 Volt car battery capable of a significant allowing a significant current through wire isn't going to kill you by touching it because your body has a high enough resistance to avoid a significant current. Thus, you can't eliminate voltage from being a factor. It's really a combination of V, I, and Frequency that kills.

I used to think I was a tough guy... I had been shocked several times (accidentally) on household wires. As a result, I felt that 110V was too weak to kill me. It wasn't until I did some research for the classes I was teaching that I realized how dangerous 110V actually is. (or rather, how dangerous a 60Hz supply actually is) If we used 1000Hz as a frequency for our wiring, the number of electrocutions greatly decrease. (although that may be high enough to create problems with a surface effect)

 

[Gibsons]

2 ways to die: with prolonged contact, currents above 18 milliamps will cause the diaphragm to contract - victim suffocates. (Most adults cannot let go of a wire at about 15 milliamps (.015 amps). So, it only takes one tenth the current from 120 volts going from hand to hand to kill a person.

So apparently some people are better at uh, 'resisting' (probably a poor word choice in this context. ) the effects of electricity than others... are the reasons for this known? Something like skin conductivity, amount of fat...?

 

[FrankSchwab]

Personal and environmental factors, I'm sure. Your resistivity will be different outside in North Dakota in the winter (cold dry air means no sweat on your hands, blood vessels are constricted, so high resistivity) than in Florida in the summer (humid, hot conditions means sweaty hands, lots of blood near the surface of the skin, low resistivity).

Once you get below the skin, the resistivity of the body decreases drastically - something about your body being essentially a giant bag of saline solution.

/frank

 

[Gibsons]

Originally posted by: FrankSchwab
Personal and environmental factors, I'm sure. Your resistivity will be different outside in North Dakota in the winter (cold dry air means no sweat on your hands, blood vessels are constricted, so high resistivity) than in Florida in the summer (humid, hot conditions means sweaty hands, lots of blood near the surface of the skin, low resistivity).

Once you get below the skin, the resistivity of the body decreases drastically - something about your body being essentially a giant bag of saline solution.

/frank

yeah, I can see that, but what I'm wondering is if, under similar conditions, certain individuals will be inherently more able to let go of the wire. That is, Joe is always able to let go of the wire at a higher amperage than Bob when tested under the same circumstances (cold or hot, sweaty or clean). Is it because Joe has a higher body fat percentage, or maybe most of Joe's family is able to let go at higher voltages than most of Bob's family?

 

[DrPizza]

Hmmm... I found a better site (I hadn't tested the resistance from one hand to the other hand... that would have required crossing the room to get the multimeter) for the resistance of humans: http://www.cdc.gov/niosh/pdfs/98-131.pdf
pretty good document...

Anyway, environmental conditions will affect the resistance... I should have thought of that. Remember in (Green Mile?) when they didn't put the wet sponge on top of the head?

 

[DrPizza]

From the pdf above:

Table 1. Estimated Effects of 60 Hz AC Currents
1 mA Barely perceptible
16 mA Maximum current an average man can grasp and ?let go?
20 mA Paralysis of respiratory muscles
100 mA Ventricular fibrillation threshold
2 Amps Cardiac standstill and internal organ damage
15/20 Amps Common fuse or breaker opens circuit*
*Contact with 20 milliamps of current can be fatal. As a frame of reference, a
common household circuit breaker may be rated at 15, 20, or 30 amps.
When current greater than the 16 mA ?let go current? passes through the forearm, it stimulates
involuntary contraction of both flexor and extensor muscles. When the stronger flexors dominate,
victims may be unable to release the energized object they have grasped as long as the current flows.
If current exceeding 20 mA continues to pass through the chest for an extended time, death could
occur from respiratory paralysis. Currents of 100 mA or more, up to 2 Amps, may cause ventricular
fibrillation, probably the most common cause of death from electric shock.11 Ventricular fibrillation
is the uneven pumping of the heart due to the uncoordinated, asynchronous contraction of the ventricular
muscle fibers of the heart that leads quickly to death from lack of oxygen to the brain. Ventricular
fibrillation is terminated by the use of a defibrillator, which provides a pulse shock to the
chest to restore the heart rhythm. Cardiopulmonary resuscitation (CPR) is used as a temporary care
measure to provide the circulation of some oxygenated blood to the brain until a defibrillator can be
used.23
The speed with which resuscitative measures are initiated has been found to be critical. Immediate
defibrillation would be ideal; however, for victims of cardiopulmonary arrest, resuscitation has the
greatest rate of success if CPR is initiated within 4 minutes and advanced cardiac life support is
initiated within 8 minutes (National Conference on CPR and ECC, 1986).6
The presence of moisture from environmental conditions such as standing water, wet clothing, high
humidity, or perspiration increases the possibility of a low-voltage electrocution. The level of
current passing through the human body is directly related to the resistance of its path through the
body. Under dry conditions, the resistance offered by the human body may be as high as 100,000
Ohms. Wet or broken skin may drop the body?s resistance to 1,000 Ohms. The following illustrations
of Ohm?s law demonstrates how moisture affects low-voltage electrocutions. Under dry conditions,
Current=Volts/Ohms = 120/100,000 = 1 mA, a barely perceptible level of current. Under wet conditions,
Current=Volts/Ohms = 120/1,000 = 120 mA, sufficient current to cause ventricular fibrillation.
Wet conditions are common during low-voltage electrocutions.
High-voltage electrical energy quickly breaks down human skin, reducing the human body?s resistance
to 500 Ohms. Once the skin is punctured, the lowered resistance results in massive current flow,
measured in Amps. Again, Ohm?s law is used to demonstrate the action. For example, at 1,000 volts,
7
Current=Volts/Ohms = 1000/500 = 2 Amps, which can cause cardiac standstill and serious damage to
internal organs.

 

[redly]

here's another guide to voltage/frequency breakdown by country

 

[Calin]

There was some questioning about a man that died because of electrocution from an multimeter - but he perforated his skin to make a better contact. The multimeter was some "more industrial" unit, and as an ohmeter had 9V between the probes. It also had enough current capacity for some tens of milliamperes

 

[Jaimin]

I am not too sure of this, but I remember from one of my class the professor saying that the danger of 60Hz or 50Hz (one of the two, not both, but I can't remember which one) is that it is the same rate at which the heart depolarizes so you have a higher danger of cardic arrest if you get shocked from one versus the other.

 

[BitByBit]

It's POWER that kills you.
1 Volt is defined as 1 Joule per coulomb.
1 Amp is defined as 1 coulomb per second.
Multiplying these, we get: (J / C) * (C / s).
The C's cancel and we get J / s, or Joules per second, which is the equation of Power.
If you rub your feet on a thick carpet and then touch something metallic, a charge of several thousand volts will pass through you.
You don't die because the current involved is very low, and occuring over a very brief period.
This is why people survive lightning strikes.

 

[f95toli]

No, I am quite sure it is the current.
Wheter or not 10J will kill you depends on the current involved, as you pointed out voltage is not dangerous so 10 000V and 1mA is "better" than 100V and 100mA (both equal 10J).

The reason is simply that you do not die because you are "cooked" or burned (which is what power does), but because the body uses an electrochemical system to transmitt signals; an alternating current will cause that system to fail and your nervous system shuts down causing cardiac arrest; sometimes withour leaving any no burn marks or any other trace on the body.
This is why CPR is so important in accidents involving electricity, since there is (often) nothing wrong with the body many vicitims will be ok if you can "jump start" the heart again.

BTW, from what I've been told 50Hz (which is what we use where I live)is more dangerous than 60Hz, I was once shown a chart with many different frequencies and how lethal they are; there is a peak (=more likely to die) around 50 Hz; 60 Hz is slightly less dangerous and 40 Hz or 70 Hz would be much safer.

 

[PowerEngineer]

Originally posted by: f95toli
...you do not die because you are "cooked" or burned...

In some instances the injury is caused by the heat generated by large currents flowing through body tissues, particularly when lightning or direct contact with a high voltage line is involved.

 

[jagec]

Originally posted by: FrankSchwab

Once you get below the skin, the resistivity of the body decreases drastically - something about your body being essentially a giant bag of saline solution.

Probably an urban legend, but I heard a story about a Navy guy who managed to electrocute himself using the 9V battery on a multimeter. The story says he was trying to measure his "internal resistance" and basically stuck a test lead in his right hand, and another in his left....

 

[Calin]

Originally posted by: BitByBit
It's POWER that kills you.
1 Volt is defined as 1 Joule per coulomb.
1 Amp is defined as 1 coulomb per second.
Multiplying these, we get: (J / C) * (C / s).
The C's cancel and we get J / s, or Joules per second, which is the equation of Power.
If you rub your feet on a thick carpet and then touch something metallic, a charge of several thousand volts will pass through you.
You don't die because the current involved is very low, and occuring over a very brief period.
This is why people survive lightning strikes.

I don't know about you, but I heard that the Coulomb is defined as an Ampere multiplied by a second (and an Ampere is defined as the current that creates a certain attraction effect between two wires).

 

[Calin]

Originally posted by: jagec

Originally posted by: FrankSchwab

Once you get below the skin, the resistivity of the body decreases drastically - something about your body being essentially a giant bag of saline solution.

Probably an urban legend, but I heard a story about a Navy guy who managed to electrocute himself using the 9V battery on a multimeter. The story says he was trying to measure his "internal resistance" and basically stuck a test lead in his right hand, and another in his left....

On a site with urban legends - he perforated its skin. It was decided that it wasn't a legend, but a reality.

 

[BitByBit]

I don't know about you, but I heard that the Coulomb is defined as an Ampere multiplied by a second (and an Ampere is defined as the current that creates a certain attraction effect between two wires).

A = C / s.
Rearranging, gives: C = As.

I'm not a biologist, and am not concerned with what physically happens to you when you are subject to an electrical current.
What I'm saying is, for that current to do damage, a sufficient amount of energy must be involved to do the necessary work.

 

[f95toli]

Sure. but that amount of work is extremely small (you only need enough voltage to induce 20mA of current, if the resistance is small enough 1V could kill you) ; hence the amount of power does not really tell you anything about how dangerous it is.

 

[ndolf]

yeah, it is not the energy that kills you but the electric signal frequency, and WHO THE HELL CAME UP WITH SUCH A CLOSE NUMBER TO OUR HEARTBEAT?

 

[Calin]

Originally posted by: BitByBit

I don't know about you, but I heard that the Coulomb is defined as an Ampere multiplied by a second (and an Ampere is defined as the current that creates a certain attraction effect between two wires).

A = C / s.
Rearranging, gives: C = As.

I'm not a biologist, and am not concerned with what physically happens to you when you are subject to an electrical current.
What I'm saying is, for that current to do damage, a sufficient amount of energy must be involved to do the necessary work.

Considering the electical signals that drive us are very small, the amount of energy needed is quite small. The work must be bigger than some thousands/tens of thousands of nerve cells are capable to do, and this is small by any kind of energy measurement.
An ampere is equal to one coulomb per second, but it isn't defined as such. An coulomb is equal to an ampere times one second, and is defined as such. (however, there are 12 years since I learned this, so I might be wrong)

 

[DrPizza]

Originally posted by: Calin

Originally posted by: BitByBit

I don't know about you, but I heard that the Coulomb is defined as an Ampere multiplied by a second (and an Ampere is defined as the current that creates a certain attraction effect between two wires).

A = C / s.
Rearranging, gives: C = As.

I'm not a biologist, and am not concerned with what physically happens to you when you are subject to an electrical current.
What I'm saying is, for that current to do damage, a sufficient amount of energy must be involved to do the necessary work.

Considering the electical signals that drive us are very small, the amount of energy needed is quite small. The work must be bigger than some thousands/tens of thousands of nerve cells are capable to do, and this is small by any kind of energy measurement.
An ampere is equal to one coulomb per second, but it isn't defined as such. An coulomb is equal to an ampere times one second, and is defined as such. (however, there are 12 years since I learned this, so I might be wrong)

Nope, you're right. A coulomb is defined in terms of 1 Ampere. That's why a coulomb is 6.25x10^18 electrons and not some nice number.

 

[Passions]

Wow this is so nuts, I was going to post the same exact question. 50hz vs 60 hz, and 110v versus 220v.

WOWOWOWO!

 

[Stiganator]

in response to inherent resistance to electric induced paralysis. I don't believe body shape,size etc plays a significant role. The skin has a high resistance about 20kohm iirc. Once the current is through the skin it is the bad times, very little resistance like maybe 1k through the entire arm and chest cavity. It takes only a minor jolt to the SA node to knock it out of sync, remember your one hand rule!!!

 

[Googer]

Originally posted by: blahblah99
Because we're the only ass-backward country in the world that likes to do things differently... left hand driving, 60hz, imperial units,...

Don't forget NTSC (vsPAL)

 

[redly]

link to another forum discussing historical power line frequencies

another link