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#16
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Lightning and modems
On Thu, 2 Oct 2014 11:41:30 -0600, Buffalo wrote:
When I leave for a long period of time, I not only unplug the power cord to the computer, I also unplug the Cat cable from my computer, just in case. Is it necessary even though I have an APC Battery Backup with built in suppressors, I don't know, but I feel better that way. A few years ago we had a lightening strike near to us and every switch port and system on a north/south running cable blew while those on the west/east running ones survived. In August this year it was the opposite where the west/east running cabled ports blew. So I'd say it is worth doing if you are happy to do it but I don't unplug. An 8 port gigabit switch isn't expensive and I've usually got a spare PCI network card. I buy 8 port switches even though I only use about 4 ports and it might take 20 years for me to loose 4 ports because it is a rare occurrence. -- Faster, cheaper, quieter than HS2 and built in 5 years; UKUltraspeed http://www.500kmh.com/ |
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#17
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Lightning and modems
On 9/30/2014 2:54 PM, Ken Blake, MVP wrote:
On Tue, 30 Sep 2014 14:52:11 -0400, wrote: On Tue, 30 Sep 2014 08:16:18 -0700, "Ken Blake, MVP" wrote: On Mon, 29 Sep 2014 20:39:54 -0400, wrote: Do *not* rely on using surge protectors. Most of them are little more than fancy extension cords, and offer next to no real protection. If you buy decent surge protectors and assure your grounding is good, there is no reason to ever unplug anything. I completely disagree. First, note that a decent surge protector is expensive, the better part of $100. Those that are around $15-25 are useless junk. Somewhat true Second, even the best surge protector can do nothing more than substantially reduce the risk. It can not eliminate it. The only way to eliminate risk entirely is to unplug. If you never took it out of the box it would last forever. Are you going to rush home from work to unplug everything? No. First of all, I'm retired these days, so I don't have to rush home from work. Second, when I was working, and even now, when I'm not, if I was leaving the house for any length of time, if thunderstorms were forecast, I would unplug before leaving. And regardless of forecasts, if I were leaving for multiple days, I would unplug before leaving. Excellent and reliable information on surges and surge protection is available from the IEEE: http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf A simpler guide aimed at the unwashed masses is available from the NIST: http://pml.nist.gov/spd-anthology/fi...es_happen!.pdf What gfretwell has written is consistent with both guides (except I don't think they include ferrite cores). I don't think 'unplugging' is in either of them. Lots of places in high lightning areas have equipment that is not practical to unplug and the equipment survives - protection is not that difficult. But do what you want. If you unplug, you probably need to unplug everything, including phone, .... And by the way, the best kind of surge protector is a whole house surge protector, not any of those that go between the computer and the electrical outlet. That is just the first line of defense, not the whole solution That's fine. I don't disagree with that point of view. The IEEE and NIST include both service panel and plug-in protectors. (Also electrical system earthing, and connecting all wiring to the house through entry protectors that are connected with a short wire to a common bonding point on earthing system. Coax ground blocks do not provide surge protection.) When using plug-in protectors, all interconnected equipment needs to be connected to the same protector. External connections, like coax also must go through the protector. As explained in the IEEE guide (starting page 30) plug-in protectors work primarily by limiting the voltage from each wire to the ground at the protector. To do that all wires must go through the protector. The NIST surge guide suggests that most damage is from high voltage between power and signal wires. The author of the NIST surge guide looked at the energy that could be absorbed in a plug-in protector using US wiring systems. Branch circuits were 10m and longer, and surges were up to the largest with any reasonable probability of occurring. The maximum energy was a surprisingly small 35 joules. In 13 of 15 cases it was 1 joule or less. (And the largest surges did not produce the largest energy.) Exposure is less than you probably imagine. Plug-in protectors with much higher ratings are readily available. High ratings mean long life for both plug-in and service panel protectors. |
#18
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Lightning and modems
I am in the lightning capital of the world and I have not lost
anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. |
#19
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Lightning and modems
Norm X wrote:
I am in the lightning capital of the world and I have not lost anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. Then what's this fuss all about ? http://www.kp44.org/LightningProtect..._Standards.php Same sort of practical advice. http://l-36.com/read_html.php?file=l...g%20Protection I have to laugh at this section. "You are two miles from shore. The thunderstorm which is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!" And the following is what happens if you don't check your weather radio. ******* Just sit right back And you'll hear a tale A tale of a fateful trip, That started from this tropic port, Aboard this tiny ship. The mate was a mighty sailin' man, The Skipper brave and sure, Five passengers set sail that day, For a three hour tour, A three hour tour. The weather started getting rough, The tiny ship was tossed. If not for the courage of the fearless crew The Minnow would be lost. The Minnow would be lost. The ship set ground on the shore Of this uncharted desert isle With Gilligan, The Skipper too. The millionaire And his wife, The movie star, The professor and Mary Ann, Here on Gilligan's Isle. Paul |
#20
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Lightning and modems
"Paul" wrote in message ...
Norm X wrote: I am in the lightning capital of the world and I have not lost anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. Then what's this fuss all about ? http://www.kp44.org/LightningProtect..._Standards.php Same sort of practical advice. http://l-36.com/read_html.php?file=l...g%20Protection I have to laugh at this section. "You are two miles from shore. The thunderstorm which is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!" That link also says: " This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! And the spark plug gap is but a fraction of an inch! " 15 volts will not jump a normal spark plug gap and neither will 200 volts. Most of the time the voltage is well above 10,000 volts. Just makes me wonder how knowledgeable the author is on the high voltage and amperage of lightning. Ah yes, Gilligan's Island. -- Buffalo |
#21
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Lightning and modems
"Buffalo" wrote in message ...
"Paul" wrote in message ... Norm X wrote: I am in the lightning capital of the world and I have not lost anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. Then what's this fuss all about ? http://www.kp44.org/LightningProtect..._Standards.php Same sort of practical advice. http://l-36.com/read_html.php?file=l...g%20Protection I have to laugh at this section. "You are two miles from shore. The thunderstorm which is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!" That link also says: " This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! And the spark plug gap is but a fraction of an inch! " 15 volts will not jump a normal spark plug gap and neither will 200 volts. Most of the time the voltage is well above 10,000 volts. Just makes me wonder how knowledgeable the author is on the high voltage and amperage of lightning. Ah yes, Gilligan's Island. But, once the air is ionized, then it might only take the low amt of voltage to continue the arc. Perhaps that is what he was talking about. -- Buffalo |
#22
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Lightning and modems
Buffalo wrote:
"Buffalo" wrote in message ... "Paul" wrote in message ... Norm X wrote: I am in the lightning capital of the world and I have not lost anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. Then what's this fuss all about ? http://www.kp44.org/LightningProtect..._Standards.php Same sort of practical advice. http://l-36.com/read_html.php?file=l...g%20Protection I have to laugh at this section. "You are two miles from shore. The thunderstorm which is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!" That link also says: " This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! And the spark plug gap is but a fraction of an inch! " 15 volts will not jump a normal spark plug gap and neither will 200 volts. Most of the time the voltage is well above 10,000 volts. Just makes me wonder how knowledgeable the author is on the high voltage and amperage of lightning. Ah yes, Gilligan's Island. But, once the air is ionized, then it might only take the low amt of voltage to continue the arc. Perhaps that is what he was talking about. Let's say the breakdown voltage of dry air was 50,000 volts per inch. If we had 100,000,000 volts to work with, that's 2000 inches or 167 feet. That means we can't get a good discharge, without some other mechanism at work. That's where ionization and eventual plasma formation come in. Which aren't discussed in enough detail here, for my liking. http://science.howstuffworks.com/nat...lightning2.htm The lightning bolt can go "up and down" several times, when a bolt hits. So the process is pretty complicated. And as that page points out, everything involving lightning involves the "assignment of probabilities". Using lightning protection structures, does not guarantee where the bolt will hit. It improves the probability a bit, that you are in control of where it goes, but the lightning can still surprise you, shoot through the side of the house, and so on. When they tell you to stand in a certain place to be safe, it's not really a guarantee of your safety (the so-called "cone of protection"). Things that are safe bets, would be standing tangentially versus radially, to an object affording protection. As the electric field when the bolt strikes the ground, makes "circular rings of potential difference" at ground zero point. If you're standing radially with respect to where the bolt hits, a potential is placed between your two feet, and your balls get burned :-) If you're standing tangentially to the rings of potential difference, there is no potential difference between your feet. Maybe the best advice, is to stand with your feet... really close together :-) Just in case you're a bit too flustered at the time, figuring out what is radial and what is tangential. And why did this tree just fall on me. Paul |
#23
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Lightning and modems
"Paul" wrote in message ...
Buffalo wrote: "Buffalo" wrote in message ... "Paul" wrote in message ... Norm X wrote: I am in the lightning capital of the world and I have not lost anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. Then what's this fuss all about ? http://www.kp44.org/LightningProtect..._Standards.php Same sort of practical advice. http://l-36.com/read_html.php?file=l...g%20Protection I have to laugh at this section. "You are two miles from shore. The thunderstorm which is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!" That link also says: " This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! And the spark plug gap is but a fraction of an inch! " 15 volts will not jump a normal spark plug gap and neither will 200 volts. Most of the time the voltage is well above 10,000 volts. Just makes me wonder how knowledgeable the author is on the high voltage and amperage of lightning. Ah yes, Gilligan's Island. But, once the air is ionized, then it might only take the low amt of voltage to continue the arc. Perhaps that is what he was talking about. Let's say the breakdown voltage of dry air was 50,000 volts per inch. If we had 100,000,000 volts to work with, that's 2000 inches or 167 feet. That means we can't get a good discharge, without some other mechanism at work. That's where ionization and eventual plasma formation come in. Which aren't discussed in enough detail here, for my liking. http://science.howstuffworks.com/nat...lightning2.htm The lightning bolt can go "up and down" several times, when a bolt hits. So the process is pretty complicated. And as that page points out, everything involving lightning involves the "assignment of probabilities". Using lightning protection structures, does not guarantee where the bolt will hit. It improves the probability a bit, that you are in control of where it goes, but the lightning can still surprise you, shoot through the side of the house, and so on. When they tell you to stand in a certain place to be safe, it's not really a guarantee of your safety (the so-called "cone of protection"). Things that are safe bets, would be standing tangentially versus radially, to an object affording protection. As the electric field when the bolt strikes the ground, makes "circular rings of potential difference" at ground zero point. If you're standing radially with respect to where the bolt hits, a potential is placed between your two feet, and your balls get burned :-) If you're standing tangentially to the rings of potential difference, there is no potential difference between your feet. Maybe the best advice, is to stand with your feet... really close together :-) Just in case you're a bit too flustered at the time, figuring out what is radial and what is tangential. And why did this tree just fall on me. Paul If you stand with your feet apart and are perpendicular to the rings, then most likely you heart will suffer more than your balls. But, by saying a spark will jump the gap of an automobile spark plug with as low as 15volts, is total nonsense. Standing, or better yet squatting with your feet together (if your balance is good enough) or sitting on the ground with your feet together and touching your butt 'may' even be better. Sitting in a bar and having a drink would even be safer. -- Buffalo |
#24
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Lightning and modems
Buffalo wrote:
"Paul" wrote in message ... Buffalo wrote: "Buffalo" wrote in message ... "Paul" wrote in message ... Norm X wrote: I am in the lightning capital of the world and I have not lost anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. Then what's this fuss all about ? http://www.kp44.org/LightningProtect..._Standards.php Same sort of practical advice. http://l-36.com/read_html.php?file=l...g%20Protection I have to laugh at this section. "You are two miles from shore. The thunderstorm which is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!" That link also says: " This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! And the spark plug gap is but a fraction of an inch! " 15 volts will not jump a normal spark plug gap and neither will 200 volts. Most of the time the voltage is well above 10,000 volts. Just makes me wonder how knowledgeable the author is on the high voltage and amperage of lightning. Ah yes, Gilligan's Island. But, once the air is ionized, then it might only take the low amt of voltage to continue the arc. Perhaps that is what he was talking about. Let's say the breakdown voltage of dry air was 50,000 volts per inch. If we had 100,000,000 volts to work with, that's 2000 inches or 167 feet. That means we can't get a good discharge, without some other mechanism at work. That's where ionization and eventual plasma formation come in. Which aren't discussed in enough detail here, for my liking. http://science.howstuffworks.com/nat...lightning2.htm The lightning bolt can go "up and down" several times, when a bolt hits. So the process is pretty complicated. And as that page points out, everything involving lightning involves the "assignment of probabilities". Using lightning protection structures, does not guarantee where the bolt will hit. It improves the probability a bit, that you are in control of where it goes, but the lightning can still surprise you, shoot through the side of the house, and so on. When they tell you to stand in a certain place to be safe, it's not really a guarantee of your safety (the so-called "cone of protection"). Things that are safe bets, would be standing tangentially versus radially, to an object affording protection. As the electric field when the bolt strikes the ground, makes "circular rings of potential difference" at ground zero point. If you're standing radially with respect to where the bolt hits, a potential is placed between your two feet, and your balls get burned :-) If you're standing tangentially to the rings of potential difference, there is no potential difference between your feet. Maybe the best advice, is to stand with your feet... really close together :-) Just in case you're a bit too flustered at the time, figuring out what is radial and what is tangential. And why did this tree just fall on me. Paul If you stand with your feet apart and are perpendicular to the rings, then most likely you heart will suffer more than your balls. But, by saying a spark will jump the gap of an automobile spark plug with as low as 15volts, is total nonsense. Yeah, I'd say! :-) So, so much for that link! Next thing I expect to hear is about people getting electrocuted off of a 12V car battery! Uh-huh! |
#25
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Lightning and modems
"Bill in Co" wrote in message
... Buffalo wrote: "Paul" wrote in message ... Buffalo wrote: "Buffalo" wrote in message ... "Paul" wrote in message ... Norm X wrote: I am in the lightning capital of the world and I have not lost anything in 30 years. I live on the Western side of the Salish Sea (not Salton Sea) and no one remembers lightning nor static electricity. I guess the salt air is a good conductor. Then what's this fuss all about ? http://www.kp44.org/LightningProtect..._Standards.php Same sort of practical advice. http://l-36.com/read_html.php?file=l...g%20Protection I have to laugh at this section. "You are two miles from shore. The thunderstorm which is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!" That link also says: " This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! And the spark plug gap is but a fraction of an inch! " 15 volts will not jump a normal spark plug gap and neither will 200 volts. Most of the time the voltage is well above 10,000 volts. Just makes me wonder how knowledgeable the author is on the high voltage and amperage of lightning. Ah yes, Gilligan's Island. But, once the air is ionized, then it might only take the low amt of voltage to continue the arc. Perhaps that is what he was talking about. Let's say the breakdown voltage of dry air was 50,000 volts per inch. If we had 100,000,000 volts to work with, that's 2000 inches or 167 feet. That means we can't get a good discharge, without some other mechanism at work. That's where ionization and eventual plasma formation come in. Which aren't discussed in enough detail here, for my liking. http://science.howstuffworks.com/nat...lightning2.htm The lightning bolt can go "up and down" several times, when a bolt hits. So the process is pretty complicated. And as that page points out, everything involving lightning involves the "assignment of probabilities". Using lightning protection structures, does not guarantee where the bolt will hit. It improves the probability a bit, that you are in control of where it goes, but the lightning can still surprise you, shoot through the side of the house, and so on. When they tell you to stand in a certain place to be safe, it's not really a guarantee of your safety (the so-called "cone of protection"). Things that are safe bets, would be standing tangentially versus radially, to an object affording protection. As the electric field when the bolt strikes the ground, makes "circular rings of potential difference" at ground zero point. If you're standing radially with respect to where the bolt hits, a potential is placed between your two feet, and your balls get burned :-) If you're standing tangentially to the rings of potential difference, there is no potential difference between your feet. Maybe the best advice, is to stand with your feet... really close together :-) Just in case you're a bit too flustered at the time, figuring out what is radial and what is tangential. And why did this tree just fall on me. Paul If you stand with your feet apart and are perpendicular to the rings, then most likely you heart will suffer more than your balls. But, by saying a spark will jump the gap of an automobile spark plug with as low as 15volts, is total nonsense. Yeah, I'd say! :-) So, so much for that link! Next thing I expect to hear is about people getting electrocuted off of a 12V car battery! Uh-huh! Depends if you are standing with your feet apart and parallel to the battery posts or perpendicular to the line of the battery posts. That link does have a lot of useful and accurate info, AFAIK. -- Buffalo |
#26
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Lightning and modems
Bill in Co wrote:
Yeah, I'd say! :-) So, so much for that link! Next thing I expect to hear is about people getting electrocuted off of a 12V car battery! Uh-huh! You can be electrocuted from as little as 1.5V. It's a matter of making a good connection, and getting the current flow to go through your heart. It's the level of current flow that counts. High voltage just makes it easier to get the necessary current level (V/R = I, large V gives large I). Holding two paddles in your hands, with 1.5V applied, will not do it. However, using needles penetrating the skin of your body, can arrange the necessary conditions. A certain level of resistance to electrical flow is expected, for "contact with palms" type events. We have certain expectations of our ability to resist the effects of electricity, based on an assumption of "dry palms". Some people's hands are a lot damper than others, which makes a difference to their perception of what is dangerous. http://en.wikipedia.org/wiki/Electric_shock "If an electrical circuit is established by electrodes introduced in the body, bypassing the skin, then the potential for lethality is much higher if a circuit through the heart is established. This is known as a microshock. Currents of only 10 µA can be sufficient to cause fibrillation in this case. [citation needed]" And with no citation, the comment is not worth much to us. I had a professor in university, who was a biomedical engineer, and he used to regale us with stories of electrical accidents at the hospital he worked at. It's easy to damage people who are naked, and have all sorts of monitors connected, then use equipment which cauterizes (like during surgery). Any electrical wiring mistakes or bad assumptions, can cause real misery. He told us stories of various body parts getting burned, while a patient is unconscious and some electricity is flowing where it should not. So talk to a biomedical engineer about the kind of mistakes that happen with electricity. Paul |
#27
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Lightning and modems
"Paul" wrote in message ...
Bill in Co wrote: Yeah, I'd say! :-) So, so much for that link! Next thing I expect to hear is about people getting electrocuted off of a 12V car battery! Uh-huh! You can be electrocuted from as little as 1.5V. It's a matter of making a good connection, and getting the current flow to go through your heart. Total bs. You are ultra sharp with computers, but I'm afraid you are out of your expertise here. Perhaps 1.5v fed directly to a naked heart could cause a problem, but an electrocution on a person by 1.5v is not possible. ****, sometimes they have a difficult time killing someone in an Electric Chair. Ever stick your tongue on a 9 v battery to see if it is still potent? Chances of getting electrocuted by doing that is nil. Heard many stories of people getting electrocuted by an electric welding machine? Very high amperage and low voltage. -- Buffalo |
#28
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Lightning and modems
Paul wrote:
Bill in Co wrote: Yeah, I'd say! :-) So, so much for that link! Next thing I expect to hear is about people getting electrocuted off of a 12V car battery! Uh-huh! You can be electrocuted from as little as 1.5V. It's a matter of making a good connection, and getting the current flow to go through your heart. It's the level of current flow that counts. High voltage just makes it easier to get the necessary current level (V/R = I, large V gives large I). Holding two paddles in your hands, with 1.5V applied, will not do it. However, using needles penetrating the skin of your body, can arrange the necessary conditions. A certain level of resistance to electrical flow is expected, for "contact with palms" type events. We have certain expectations of our ability to resist the effects of electricity, based on an assumption of "dry palms". Some people's hands are a lot damper than others, which makes a difference to their perception of what is dangerous. http://en.wikipedia.org/wiki/Electric_shock "If an electrical circuit is established by electrodes introduced in the body, bypassing the skin, then the potential for lethality is much higher if a circuit through the heart is established. This is known as a microshock. Currents of only 10 µA can be sufficient to cause fibrillation in this case. [citation needed]" And with no citation, the comment is not worth much to us. I had a professor in university, who was a biomedical engineer, and he used to regale us with stories of electrical accidents at the hospital he worked at. It's easy to damage people who are naked, and have all sorts of monitors connected, then use equipment which cauterizes (like during surgery). Any electrical wiring mistakes or bad assumptions, can cause real misery. He told us stories of various body parts getting burned, while a patient is unconscious and some electricity is flowing where it should not. So talk to a biomedical engineer about the kind of mistakes that happen with electricity. Paul When I mean by "getting electrocuted", I don't count such things as sticking electrodes into your heart (or even brain for that matter) and attaching a car battery. :-) As that's never going to happen in practice. :-) |
#29
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Buffalo wrote:
"Paul" wrote in message ... Bill in Co wrote: Yeah, I'd say! :-) So, so much for that link! Next thing I expect to hear is about people getting electrocuted off of a 12V car battery! Uh-huh! You can be electrocuted from as little as 1.5V. It's a matter of making a good connection, and getting the current flow to go through your heart. Total bs. You are ultra sharp with computers, but I'm afraid you are out of your expertise here. Perhaps 1.5v fed directly to a naked heart could cause a problem, but an electrocution on a person by 1.5v is not possible. ****, sometimes they have a difficult time killing someone in an Electric Chair. Ever stick your tongue on a 9 v battery to see if it is still potent? Chances of getting electrocuted by doing that is nil. Heard many stories of people getting electrocuted by an electric welding machine? Very high amperage and low voltage. I didn't give instructions on how to do it with 1.5V. Obvious it requires a connection pretty close to the heart muscle. It was purely to indicate the limit is pretty low, if the conditions are just right. At some point, the voltage is low enough, that conduction might not have any impact. Presumably the activation voltage of nerves and muscles has some lower limit. And then your attempts at setting a new low record, would fail. Applying a battery to your tongue, doesn't go across your heart. I'm sure a physiologist could explain why there aren't major contractions when you apply a battery to your tongue, but I can't. What kind of welding machine ? There are differences in circuit behavior, depending on power source. Whether it's a generator, alternator, transformer connected to line, or whatever. Some power sources have high open-terminal voltage. Take my bicycle generator as an example. With no load, the terminal voltage can rise as high as 50 to 100VAC. Once even a little bit of load is applied to the thing, the voltage comes down to reasonable levels again. The generator on the bicycle is speed sensitive - whereas the alternator on your car, the field winding is adjusted to give the desired output, so it's a feedback system. The bicycle generator doesn't have any feedback system, and if you run it open circuit, be careful what you touch. And no, I have no desire to verify this by touching the bicycle generator while going 20 miles an hour (no load), to see what kind of kick its got. I've worked with high voltage in home experiments, and only received one significant shock. And that was while playing with an ignition coil, and leaning on the wrong thing on my bench. I've been a lot more careful since then. Paul |
#30
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Lightning and modems
Bill in Co wrote:
Paul wrote: Bill in Co wrote: Yeah, I'd say! :-) So, so much for that link! Next thing I expect to hear is about people getting electrocuted off of a 12V car battery! Uh-huh! You can be electrocuted from as little as 1.5V. It's a matter of making a good connection, and getting the current flow to go through your heart. It's the level of current flow that counts. High voltage just makes it easier to get the necessary current level (V/R = I, large V gives large I). Holding two paddles in your hands, with 1.5V applied, will not do it. However, using needles penetrating the skin of your body, can arrange the necessary conditions. A certain level of resistance to electrical flow is expected, for "contact with palms" type events. We have certain expectations of our ability to resist the effects of electricity, based on an assumption of "dry palms". Some people's hands are a lot damper than others, which makes a difference to their perception of what is dangerous. http://en.wikipedia.org/wiki/Electric_shock "If an electrical circuit is established by electrodes introduced in the body, bypassing the skin, then the potential for lethality is much higher if a circuit through the heart is established. This is known as a microshock. Currents of only 10 µA can be sufficient to cause fibrillation in this case. [citation needed]" And with no citation, the comment is not worth much to us. I had a professor in university, who was a biomedical engineer, and he used to regale us with stories of electrical accidents at the hospital he worked at. It's easy to damage people who are naked, and have all sorts of monitors connected, then use equipment which cauterizes (like during surgery). Any electrical wiring mistakes or bad assumptions, can cause real misery. He told us stories of various body parts getting burned, while a patient is unconscious and some electricity is flowing where it should not. So talk to a biomedical engineer about the kind of mistakes that happen with electricity. Paul When I mean by "getting electrocuted", I don't count such things as sticking electrodes into your heart (or even brain for that matter) and attaching a car battery. :-) As that's never going to happen in practice. :-) In my line of business, SELV (safe extra low voltage) was defined as 48VDC. So that's an example of a pretty high value, that I'm sure you would not enjoy if you touched it. Whether it is AC or DC makes a difference. If AC, and the frequency is high enough, the skin effect takes over. The high voltage supply I've got, most of the effect from it would travel over the skin surface, and not below. So the physical effects would be burning rather than shock. One of the experiments they do in high school class, is connect thirty students to a hand cranked generator (the one with three or four horseshoe magnets). The frequency is pretty low when you slowly turn the handle... and that thing is as effective as hell :-) I'm sure you guys must have had a teacher who wanted to try that. I guess no reports headed home, to get parents excited. I certainly didn't feel the need to red flag the experiment. The generator makes something like 90V, across 30 students, and if there was just 3V across each student, it didn't feel like 3V. It felt like a lot more. Very effective. Paul |
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