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onix
02-28-2005, 05:06 PM
The US uses 60 Hz, 120V, and most of the world uses 50Hz, 210-240V. Was there some historical marketing ploy which drove these two different standards? Were these standards in place before TV?

Added March 26, 2005, 11AM (PST)

Thanks to redly for providing these awesome links:

Link1 (http://services3.ieee.org/organizations/pes/public/2003/sep/peshistory.html)

Link2 (http://electrical-contractor.net/ubb/Forum1/HTML/005567.html)


Added April 12, 2005, 9AM (PST)

And thanks to zlinker1 (his first post) for providing this link:

Link3 (http://www.pridelabs.us/adapters/)

bobsmith1492
02-28-2005, 05:36 PM
I think I heard the reason once, but don't really remember. It probably just had to do with different people developing the technology since the continents are so far separated; most of the countries in the Americas use 120/60.

PowerEngineer
02-28-2005, 11:41 PM
here's a l;ink: (http://www.answers.com/topic/alternating-current)

Most countries in the world have standardised their electricity supply systems to one of two frequencies: 50 hertz or 60 hertz. The list of 60 hertz countries, most of them in the New World, is shorter, but this is not to say that 60 hertz is less common. The 60 hertz countries are: American Samoa, Antigua and Barbuda, Aruba, Bahamas, Belize, Bermuda, Canada, Cayman Islands, Colombia, Costa Rica, Cuba, Dominican Republic, El Salvador, French Polynesia, Guam, Guatemala, Guyana, Haiti, Honduras, South Korea, Liberia, Marshall Islands, Mexico, Micronesia, Montserrat, Nicaragua, Northern Mariana Islands, Palau, Panama, Peru, Philippines, Puerto Rico, Saint Kitts and Nevis, Suriname, Taiwan, Trinidad and Tobago, Turks and Caicos Islands, United States, Venezuela, Virgin Islands (U.S.), Wake Island.[1] (http://www.philip.allen.org/voltages.htm)

The following countries have a mixture of 50 Hz and 60 Hz supplies: Bahrain, Brazil (mostly 60 Hz), Japan (60 Hz used in western prefectures).[2] (http://www.50hz.com/pwchrt2.htm)

Most countries have chosen their television standard to match their mains supply frequency.

It is generally accepted that Nikola Tesla chose 60 hertz as the lowest frequency that would not cause street lighting to flicker visibly. The origin of the 50 hertz frequency used in other parts of the world is open to debate but seems likely to be a rounding off of 60hz to the 1 2 5 10 structure popular with metric standards.

Other frequencies were somewhat common in industrial use in the first half of the 20th century, and remain in use in isolated cases today. 25 Hz power, much of it generated at Niagara Falls, was used in Ontario and the northern USA. Some 25 Hz generators were in use at Niagara Falls up until the mid-1990's, for large industrial customers who did not want to replace existing equipment. The lower frequency eases the design of low speed electric motors, especially commutator-type motors for electric traction applications such as railways, but causes a noticeable flicker in incandescent lighting.

Off-shore, textile industry, marine,computer mainframe, aircraft and spacecraft applications sometimes use 400Hz, for technical benefits of reduced weight of apparatus or higher motor speeds.

16.67 Hz power is still used in some European rail systems, such as in Sweden.

It should be noted that AC-powered appliances can give off a characteristic hum at the multiples of the frequencies of AC power that they use.

Geniere
03-01-2005, 01:07 AM
Power Engineer ? Very nice!

If the power utilities were to start with a clean sheet, what frequency do you think they would agree on?

Peter
03-01-2005, 02:16 AM
German rail also still runs on 16.7 Hz. I can tell ... everytime one of those high-speed "ICE" trains flies by, I get 16 Hz flicker on both my 20" CRTs ... although I live some 200 meters from the track.

Calin
03-01-2005, 04:53 AM
50 Hz is enough for the current incandescent light to not flicker. Also, the lower frequency makes the generators a bit more efficient (they work at a lower rpm, so they work with less mechanical resistance).
For older incandescent lights that worked at a lower temperature, maybe the flicker at 50 Hz was visible. All I can say is that now there is no problem.
Why lower/higher frequencies are preferred sometimes? The usual AC electic motors (single pole, one phase, with solenoids on the stator and a cage as the rotor) have the 0-torque rpm equal to the frequency Hz of the AC. At lower frequencies it works as a motor, at higher frequencies it works as a electomagnetic brake. If you want to use low rpm electic engine, you either use a reducing transmission, or lower frequency.
Higher frequency might be used because it can reduce the weight of the transformers (the solenoids can have lesser revolutions as the higher frequency current needs less impedance from the solenoids.

bobsmith1492
03-01-2005, 08:39 AM
I can't stand even 60 Hz flicker on fluorescent lights... I couldn't even imagine 50 Hz. :confused:

Leper Messiah
03-01-2005, 09:17 AM
^^ I concur. Same thing with my monitor. has to be at least 72hz, so I can stand it.

Calin
03-01-2005, 10:18 AM
Incandescent lights at 50 Hz have no flicker - I can tell you first hand. The fluorescent ones indeed flickers at 50 Hz, but it is visible only on periphereal vision (not that it is not disturbing this way)

onix
03-01-2005, 03:24 PM
The reason you cannot see incandesent bulb flicker is because it does not cool down (dims) sufficiently between cycles, and the 60Hz actually delivers power at 120Hz.

The nice thing about 60Hz is that it can be used to sync clocks. The accuracy at 60Hz is precise because power circuits are matched for this frequency and the power companies do not want power being reflected back.

Why 50Hz vs. 60Hz pre-TV still seems to be a mystery.

JTWill
03-01-2005, 05:51 PM
Westinghouse, for the US, It is as simple as picking a standard. The reason most countries use 240v is expense, it is one less transformer stage, It also alows for a smaller wire guage from lower current required. At 1200watts a 120volt system needs 10 amps at 240 it needs 5amps. 20amps needs the same wire size from 120v or 240v. It is cheaper to use 50Hz in power generation but you lose on the true RMS on the voltage. There is a whole science behind the use of the AC waveform .

blahblah99
03-01-2005, 08:27 PM
Because we're the only ass-backward country in the world that likes to do things differently... left hand driving, 60hz, imperial units,...

PowerEngineer
03-01-2005, 09:34 PM
The choices of 60 Hz and 50 Hz were both rather arbitrary. (There's no RMS difference)

Lower electrical frequencies require more iron in their transformers because the magnetic fields that accompany their AC currents change less rapidly and so saturate the iron more readily. On the other hand, the changing magnetic fields induce eddy currents in the iron core that obviously increase with the increased rate of change caused by higher AC freqencies. The same trade-offs apply to electrical motors too. (And that's why airplane power systems where weight is important use much higher frequencies.)

So (generally) 50 Hz transformers/motors have higher initial costs but lower operating costs and longer lives.

There is no magic for time synchronization using 60 Hz. Power systems generally maintain their nominal frequencies, but the actual frequency is fluctuating all the time (usually within +/-0.05 Hz). Inadvertent power flows triggered by frequency deviations in one direction usually cause deviations in the opposite direction when the power is returned. The integration of these frequency deviations is expressed as "time error". Indeed, a clock built to keep correct time by running at exactly the nominal frequency (either 50 Hz or 60 Hz) will run fast and slow with the actual frequency and show an accumulated "time error" in seconds. It's not that unusual for the "time error" to reach several seconds before special actions are taken, and that's more because large values signify a persistent frequency deviation than it is a concern over the accuracy of clocks.

bobsmith1492
03-01-2005, 09:57 PM
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.

Cha0s
03-01-2005, 11:45 PM
its different when it comes to light, I couldnt see it flicker at 50mhz, but i can see my monitor flicker at 75Hz..

jagec
03-01-2005, 11:59 PM
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,...

umm? /checks location just to be sure

Half the world uses 60Hz, half uses 50, it's not just the US.

We drive on the RIGHT here, like most of the world.

I agree with you about the Imperial units, though.


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.

you a hardcore Darwinist or something?;)

Calin
03-02-2005, 04:34 AM
Originally posted by: onix
The reason you cannot see incandesent bulb flicker is because it does not cool down (dims) sufficiently between cycles, and the 60Hz actually delivers power at 120Hz.

The nice thing about 60Hz is that it can be used to sync clocks. The accuracy at 60Hz is precise because power circuits are matched for this frequency and the power companies do not want power being reflected back.

Why 50Hz vs. 60Hz pre-TV still seems to be a mystery.

The nice thing about 50 Hz is that it can be used to sync clocks. I also have a radio with digital clock that takes its timing from the 50Hz of the power socket

bobsmith1492
03-02-2005, 06:11 AM
The nice thing about 60 hz is that it can be used to sync clocks. I built one myself using a small microprocessor. ;)

sharkeeper
03-02-2005, 01:07 PM
Clocks using the fundamental (analogue sinus) have the advantage of no cumulative error.

The incandescent bulb will not flicker (or produce stroboscopic effects on moving objects) as pronounced as discharge lamps due to the persistence. The attack and decay times are quite buffered. Think of it as a ripple filtered source of light. :) The eye cannot detect it but its there. Connect a solar cell to your computer's microphone IN and shine it at a tungsten bulb running on A/C once.

gsaldivar
03-03-2005, 06:30 AM
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,...

:roll:

jagec
03-03-2005, 12:58 PM
Originally posted by: Calin

Originally posted by: onix
The nice thing about 60Hz is that it can be used to sync clocks. The accuracy at 60Hz is precise because power circuits are matched for this frequency and the power companies do not want power being reflected back.


The nice thing about 50 Hz is that it can be used to sync clocks. I also have a radio with digital clock that takes its timing from the 50Hz of the power socket

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

Calin
03-04-2005, 04:29 AM
:D

Bassyhead
03-07-2005, 08:51 AM
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.

Calin
03-07-2005, 09:16 AM
Sometimes the houses catch fire because of the overheating wires in the walls. In this case, higher voltage = lower current = lower heat in the wall.
And the voltage that can kill you in a bathroom is around 50 V (or maybe less). So the fatality rate depends alot of other things

thunderroller
03-08-2005, 08:43 PM
that depands upon the power genration sorce

Concillian
03-09-2005, 08:12 PM
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
03-10-2005, 10:27 AM
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
03-10-2005, 10:43 AM
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
03-10-2005, 10:49 AM
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
03-10-2005, 11:05 AM
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
03-10-2005, 11:44 AM
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
03-10-2005, 11:45 AM
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
03-10-2005, 02:12 PM
here's another guide to voltage/frequency breakdown by country (http://www.panelcomponents.com/ic/guide.htm)

Calin
03-11-2005, 03:50 AM
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
03-12-2005, 11:39 PM
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
03-13-2005, 07:36 AM
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
03-13-2005, 06:39 PM
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
03-13-2005, 11:06 PM
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
03-14-2005, 03:08 AM
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
03-14-2005, 03:15 AM
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
03-14-2005, 03:17 AM
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
03-14-2005, 05:53 AM
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
03-14-2005, 07:42 AM
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
03-14-2005, 08:30 AM
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
03-14-2005, 09:53 AM
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
03-14-2005, 12:03 PM
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
03-24-2005, 04:47 PM
Wow this is so nuts, I was going to post the same exact question. 50hz vs 60 hz, and 110v versus 220v.

WOWOWOWO!

Stiganator
03-25-2005, 05:14 PM
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
03-25-2005, 11:13 PM
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
03-26-2005, 04:01 AM
link to another forum discussing historical power line frequencies (http://electrical-contractor.net/ubb/Forum1/HTML/005567.html)

another link (http://services3.ieee.org/organizations/pes/public/2003/sep/peshistory.html)

zlinker1
04-11-2005, 04:38 AM
Before this 60 Hz bashing session gets out of hand, consider this:

Voltage and frequency

Europe and most other countries in the world use a voltage which is twice that of the US. It is between 220 and 240 volts, whereas in Japan and in most of the Americas the voltage is between 100 and 127 volts.

The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth century creative genius named Nicola Tesla. He made many careful calculations and measurements and found out that 60 Hz (Hertz, cycles per second) was the best frequency for alternating current (AC) power generating. He preferred 240 volts, which put him at odds with Thomas Edison, whose direct current (DC) systems were 110 volts. Perhaps Edison had a useful point in the safety factor of the lower voltage, but DC couldn't provide the power to a distance that AC could.

When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 didn't fit the metric standard unit sequence (1,2,5). At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II the 50-cycle standard was established. A big mistake, however.

Not only is 50 Hz 20% less effective in generation, it is 10-15% less efficient in transmission, it requires up to 30% larger windings and magnetic core materials in transformer construction. Electric motors are much less efficient at the lower frequency, and must also be made more robust to handle the electrical losses and the extra heat generated. Today, only a handful of countries (Peru, Ecuador, Guyana, the Philippines and South Korea) follow Tesla?s advice and use the 60 Hz frequency together with a voltage of 220-240 V.

Originally Europe was 110 V too, just like Japan and the US today. It has been deemed necessary to increase voltage to get more power with less losses and voltage drop from the same copper wire diameter. At the time the US also wanted to change but because of the cost involved to replace all electric appliances, they decided not to. At the time (50s-60s) the average US household already had a fridge, a washing-machine, etc., but not in Europe.

The end result is that now, the US seems not to have evolved from the 50s and 60s, and still copes with problems as light bulbs that burn out rather quickly when they are close to the transformer (too high a voltage), or just the other way round: not enough voltage at the end of the line (105 to 127 volt spread !).

Note that currently all new American buildings get in fact 230 volts split in two 115 between neutral and hot wire. Major appliances, such as ovens, are now connected to 230 volts. Americans who have European equipment, can connect it to these outlets.

http://www.pridelabs.us/adapters/


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,...

Geniere
04-11-2005, 08:39 PM
[quote]
Originally posted by: zlinker1...

Welcome and nice post. You and a few others in this thread have got it right but mis-info abounds.

nomadwind
04-11-2005, 09:55 PM
Interesting post; being one that's currently studying electrical engineering, I just can't help joining in :). Hi everyone.

Pertaining to the statement of Nikola Tesla's choice of 60Hz to avoid flickering, perhaps I may add, as I've read from the book "Tesla: Man Out of Time", it seems Tesla had some obsessive-compulsive tendencies, and preferred things that were divisible by the number 3 to produce round numbers. Looking at 50Hz and 60Hz, or 110Hz and 240Hz, it is quite obvious based on that factor, isn't it?

As for voltage frequencies, higher frequency would provide a better quality signal (when coupled with other necessary components, such as capacitors, etc) in the context of electricity usage. As a reference, let's consider the switching power supply. There's a pulse-width modulation circuit which is used switch the voltage on-and-off at a high rate. Generally, the switched voltage is about 40kHz. In a timeframe (let's say 1 second), the peak voltage (or rather, the signal flowing through) is achieved that many times.

Because of that, one could say that the current that flows is constantly switched on-and-off too. Supposing 40kHz, the amount of time for the current to flow is very small - in another way, the charge is less too (q=It or I=q/t). Taking the human body into perspective, with such high frequencies, there might not be enough of a charge to penetrate the body. Also, the "alternating" in A.C. isn't there for nothing - I'm not sure of how to explain that part in this context.

(To further illustrate, consider a friend who's splashing water on you. "High current" = bucket, "low current"=peewee water pistol. You'll definitely get really drenched by the bucket, while if your friend shot at you with the water pistol, you'll still get the water on you, but you won't be as drenched immediately; consider the evaporation as the "current's dissipation" through your body.)

Since there were discussions on power, I'd like to add that power can also be calculated using P=(I^2)R (current squared multiplied by resistance) - this equation is of higher importance than P=VI in dealing practical situations, as frequently it is called (I^2)R losses - heat losses (or production of heat). This equation is both a good and bad thing. Good in the sense that many appliances utilise heat for useful work - while bad being that in most circuits, heat is a byproduct. Also, consider electrical burns.

Also, remember that Ohm's Law, V=IR, isn't fully mathemathical - considerations need to be placed since all three values may be changing in a given situation.

PowerEngineer
04-11-2005, 10:54 PM
This 50 Hertz vs. 60 Hertz question seems to be a recurring favorite (along with wireless power transmission). :)

I hadn't heard the metric explanation for 50 Hertz before, and that is interesting. I am familiar with Tesla's tendancy to favor multiples of three.

I have to take issue with the assertion that 50 Hz is "20% less effective in generation" and "10-15% less efficient in transmission". It is true that the iron cores of 50 Hz devices must be larger (i.e. contain more iron) because the slower frequency means that the magnetic fields persist longer in each direction during each cycle, and therefore tend to saturate the core iron at lower flux levels; more iron lowers the flux density and keeps the 50 Hz core from saturating. This means the 50 Hz devices should cost more initially. Otherwise, the efficency of generation and transmission is essentially the same. If anything, 50 Hz is a little more efficient because the lower freuency produces smaller eddy currents in the iron cores (and therefore lower losses) and it also produces less "skin effect" (which is the tendancy of alternating currents to produce higher current densities towards the surface of a conductor) and therefore less line losses (because a more even distribution means lower I^2 average).

It's also worth noting that most distribution circuits use volatges in the 12 to 14 kV range (before being stepped down for the household drops), which means that the choice of 120 volts or 240 volts for house wiring does not have any real impact on the problem of voltage level changes along the length of a feeder.

I'm afraid that 40 khz will never be a practical frequency for power delivery. While the "skin effect" might might save people from electrocution, that same effect would make it impossible to find a practical conductor for transmission. The rotational speed of a synchronous electric generator (or motor) is given by the formlua: RPM = 60*frequency/# of poles pairs. The speed for a simple three-phase synchronous motor with a single pair of poles (i.e. one North and one South) is 3600 RPM. It looks like you'd need 666 pole pairs to have a 3600 RPM motor at 40 khz.

Also remember that alternating current brings phase angles between currents and voltages [P=V*I*cos(phase angle)], and that reactances and capacitances must be included in determining impedances [Z = R + jX] where V=I*Z

:thumbsup:

jagec
04-12-2005, 01:12 AM
Originally posted by: zlinker1
Today, only a handful of countries (Peru, Ecuador, Guyana, the Philippines and South Korea) follow Tesla?s advice and use the 60 Hz frequency together with a voltage of 220-240 V.


Ecuador is 110V, 60Hz.

Colin1497
04-25-2005, 08:26 PM
Can't resist:

Airplanes (and other miltary vehicles) use:

28VDC,
115V, 400Hz, 3ph, or
270VDC

See Mil-Std-704E

George Powell
04-26-2005, 01:25 PM
The reason for 115V 3 phase 400Hz on aircraft is to do with power factor.

By keeping the power factor as close to a particular value as possible it is possible to make the generation and transmission systems smaller and lighter thus saving fuel and money.

28V DC and 28V AC are used for instrument buses. 270V DC is not widely used, the only one I can think of is GMIS In flight entertainment.

JTWill
04-30-2005, 12:49 AM
Originally posted by: 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?

Your heart beats at 60 times a second? :D

Indigopeacock
05-01-2005, 04:54 PM
a lot slower usually.