Andrea! I think you can claim a prize for that: they give a prize to the few = ones who survive to experiments like this... :) ----- Original Message -----=20 From: James Nick Sears=20 To: PICLIST@MITVMA.MIT.EDU=20 Sent: Sunday, February 15, 2004 7:14 PM Subject: Re: [EE:] curious Live wire experiment Be careful, Andrea. I think the rule with high voltages and the human = body is that there ultimately is no rule and that anything can happen. I interned at a recording studio when I was in college for EE and the engineer/owner, who is a very intelligent guy with a lot of = self-taught electrical knowledge told me, contrary to what intuition may first = tell you, that in countries where the mains carry 240V @ 50Hz the percentage of = shocks that result in death are actually LESS than here in America where we = use 120V @ 60Hz. The reason is, he explained, that 60Hz is close to a = frequency that regulates heartbeat (or is a frequency that is more likely to = perturb said signal). Even though more current flows with a 240V shock, it is = less likely to stop the heart and cause death. This indicates that there is a more delicate issue at play than how = many amps of current we are conducting or how many volts we apply across = the body. When I was in my early teens, my uncle gave me an old mechanical timer = (the sort that you would use to turn a light on and off while you are away) = that didn't work. I knew virtually nothing about electricity but I cracked = it open and wanted to see if I could see anything obviously wrong. I = didn't see anything but I couldn't tell whether or not the gears that drove = the timer were turning very slowly or not at all. So being the brilliant = young pup that I was I decided to try to catch one of my fingernails on one = of the gear teeth to see if I could feel any motion. Well, I'm not sure what = I touched but it was very live. I got the most intense shock that I = have had thus far in my life. Luckily I wasn't in a position where I grabbed = the power source but it still took me a moment to get my hand pulled away = and I was shocked to the point where my arm felt strange for awhile = afterward, etc. I unplugged the timer and said the hell with it. But, before learning of the 50Hz/60Hz issue, I took this experience as evidence that while getting shocked isn't fun, as long as you aren't = in the horrible situation where you are latched onto the high voltage by involuntary muscle tension, you'll be ok with a brief shock. This was = also furthered by the fact that I had a different uncle who was working = with an old power tool (before plastic insulated tools) that connected him to = 120VAC for a considerable time (he was working alone and the shock caused his muscles to tense around the tool so he couldn't let go and it was I = think maybe a minute or more before my grandfather came upon him writhing on = the floor) and he was OK, although IIRC he did go to the hospital over it. However, after hearing the 50Hz/60Hz effect, I believe (whether it is commonly accepted or not) that even a few cycles of 120VAC could be = the end of a person under the wrong circumstances. Probabilistically I would = say that the odds of getting killed by a 100ms 120V/60Hz shock are = obviously much lower than those of the same shock applied for 10s or a minute. BUT...I believe (and for my own saftey intend to continue to believe) = that a significant factor in that probability distribution is one that is in = itself for all intents and purposes random - the frequency/phase difference = between your relevant internal signals and the AC frequency. That is to say = that even a very brief shock with just the wrong timing could be the end of = a person, even after he/she has sustained a much larger and otherwise identical shock due to subtle differences in the way that the 50 or = 60Hz interacts with your body's signals. I am the first to admit that I have no hard evidence to back up this = theory, but for my purposes I don't need any. Passing significant current = through your body is a bad idea, even if you've done it a million times before = with no problems. Think of your body as a PIC with incomprehensible value. In the = datasheet it says not to connect it to mains voltage. We've all had parts that exceeded their datasheet performance. But we also know that this = behavior is not guaranteed and that at any moment while the part is operating = out of spec, a puff of smoke could be just around the corner. Be glad that = you probably can sustain the occasional shock without death, but don't = roll the dice any more than you have to. There is very little to gain and = everything to lose. Be careful, babe. :) Nick PS: If you have to play with mains voltages, I have learned from electricians that if there is ANY doubt as to the potential of the = part in question, ALWAYS test with the back of your hand before grabbing hold = of them so that if it is hot you will pull away rather than grab hold = when your muscles involuntarily tense. But you are still rolling the dice, just stacking the odds toward your favor. ----- Original Message ----- From: "Alexander JJ Rice" To: Sent: Saturday, February 21, 2004 7:10 AM Subject: Re: [EE:] curious Live wire experiment On Sat, 21 Feb 2004 12:01:58 +0100, Omega Software wrote: > Hello, > > I've always been curious to know if one can get an electric shock by > JUST touching the 230V Live wire (not the Neutral). In theory, no, you won't get an electric shock just from touching the = live wire - assuming you are insulated from your surroundings so that your = body can 'float' to the higher potential of the mains you should be fine. > A lot of people keep telling me it's impossible, yet I can measure = some > AC voltage between me and the Live wire with my multimeter (pity it > cannot measure AC current). That is because unless you are standing on an insulator like a big = plastic milk crate, you are connected to ground by whatever is touching the = floor. Conductve additives are now added to the soles of most shoes. The = above experiment is dangerous - would you trust your life to a #6.99 piece = of equipment, if the resistors in the multimeter were to flash over, you woudl get a serious electric shock. > Since the AC voltage was something like very few volts, Um... 240/110 volts, that is more than enough to push a current of = several amps through you. 20ma will usually kill you. and my body's > resistance quite high (at least at those voltages), no it isn't - sure you may have a resistance of a few Mohms at loww currents, but during an elctric shock from the mains the current penetrates the skin, vapourising it and destroying the cells, the bulk resistance of your body is quite low once this has happened, typically = a few hundred ohms. You are basically a big bucket of salty water just waiting to get zapped. I decided to try an > experiment, knowing anyway that the "automatic emergency switch" = (Ground > Surge Protection? how is it called?) would have saved me from = eventual > annoying problems. What, annoying problems... like death. This is a rediculous attitude - = a bit like - my local hospital has a good ER, why don't i go tightrope = walk across a motorway: the hospital will save me from 'annoying problems' > > I had a green led I wasn't too fond of, so I've put one pin (the = anode, > although I doubt that it matters) to the Live wire, and left the = cathode > unconnected. I turned on the switch.. and then finally put a finger = on > the cathode, thinking the LED may have started to emit some light. Don't do this, you will rapidy remove yourself from the gene pool. > Instead, I heard a loud pop and saw a shiny spark.. while the = current in > the house immediately went away (the automatic emergency switch > (lifesaver? Ground Surge Protection?) acted). > The LED wasn't damaged (!), but the pin tied to the Live 230V line = was > burned and damaged, so much that it was nearly cut. > I'd have some questions about the above experiment: > > 1) Being I insulated from earth, why did the current (and so much = of) > pass anyway? Was I the plate of a "capacitor" to earth? If so, how = big? > And what was the other plate, every thing surrounding me, maybe? At 50/60Hz the current flowing due to the 20pF or so of distributed capacitance is negligible. The reason current was flowing to earth is beacause you were probaly not insulated from earth. > 2) How much current may have passed through me, if the automatic > emergency switch didn't stop it? Enough to stop your heart, enough to give you 3rd degree burns over = parts of your body. > 3) Why the LED still works perfectly, while one of its pins is so = much > damaged? what i suspect actually happened is thaf you touched the led and = jogged it into touching the neutral or the earth, if enough current had flowed through you that you saw sparks you wouldn't have been able to type = your e-mail - theres no cybercafe in whatever from of afterlife you believe = in. > > Thanks, > Andrea Please don't do stupid stuff like this again, if you inist on doing = it, make sure you have a parent/supervisor/friend who is trained in CPR to recusitate you and take you to hospital in the likely eventuality that = you get a serious electric shock. Reagrds Alexander Rice -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! 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