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#1
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Static Electricity?
Is static electricity always accompanied by an audible (even if
slightly) spark (arc)? I guess what I am asking is if I ground myself each time before I touch the computer innards, can I be sure I have eliminated static electricity because I don't hear or feel anything? IOW, can static electricity flow from me to a metal computer innard without my knowing it? While I am simply standing there holding onto a metal computer part? If you think this is a dumb question - just ignore it. Thanks |
#2
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"geezer" wrote in message ... Is static electricity always accompanied by an audible (even if slightly) spark (arc)? I guess what I am asking is if I ground myself each time before I touch the computer innards, can I be sure I have eliminated static electricity because I don't hear or feel anything? IOW, can static electricity flow from me to a metal computer innard without my knowing it? While I am simply standing there holding onto a metal computer part? If you think this is a dumb question - just ignore it. Thanks There is no way to be sure you have eliminated the static. Grounding straps are made to help keep the static under control. They are a wrist strap that you should wear on the hand you use to work on the computer with. The strap is grounded with a resistor inseries with the wire so that you will not be harmed if you do hapen to contact a live wire. As the computer circuits operate under 12 volts it will not take much static to harm the parts. YOu might look at it as a 12 volt car battery will not spark if you touch it, but put a wire across the terminals and you can see the results of the vlotage. Usually about 40 to 50 volts is hard to feel if your skin is dry. With all that said, static is not really that bad. It is usually worse in the winter as there is not much humidity in the air. The humidity helps bleed off the static. |
#3
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On Fri, 18 Feb 2005 18:43:47 GMT, geezer
wrote: Is static electricity always accompanied by an audible (even if slightly) spark (arc)? No, definitely not. That would only be seen with a relatively high voltage. I guess what I am asking is if I ground myself each time before I touch the computer innards, can I be sure I have eliminated static electricity because I don't hear or feel anything? No, you can be sure you have eliminated static because you grounded yourself, has nothing to do with the hearing or feeling of anything. That is, so long as you STAY grounded. IOW, can static electricity flow from me to a metal computer innard without my knowing it? yes While I am simply standing there holding onto a metal computer part? It would happen when you first touch that part, not while continuing to hold same electrically continuous part, OR after building up a charge, then touching that part to another part. For example, if you were grounded when you picked up a memory module, and continued to hold the exact same spot on that module (ignoring moisture changes from hands, etc) you could shuffle around on the floor and should be OK, UNTIL you touch that memory module to something that is grounded, like the motherboard. The discharge went from you, through the memory, and out to the motherboard. not only should you ground yourself, but be at same potential as the component ground you're working on... which should also be grounded. If you think this is a dumb question - just ignore it. Ok. |
#4
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Static electricity is in the order of many thousands of volts. Fortunately
the current source is extremely low, or it would be lethal. Because its voltage is so high, it can jump or arch to objects, circuit boards, and anything that conducts to ground. The devices used in modern electronics can easily be damaged from static electricity. Touching the main computer case, or metal frame (chassis) of the computer, before, and keep touching at the same time as touching a card, will prevent a static discharge to the card. I have seen static discharges cause failures to keyboards, mice, and even ports on computers as soon as the user goes to use the computer. Sometimes the user is plugging something in to the computer, and when he inserts the wire in to the port connector, the port is damaged from a static discharge. It is best to touch the metal part of the case of the computer, before connecting something to a port. In a computer room, there should not be any materials that promote the generation of static electricity. It is best to have a humidifier running, and keep the room humidity to at least 50% to 60%. -- Jerry G. ====== "geezer" wrote in message ... Is static electricity always accompanied by an audible (even if slightly) spark (arc)? I guess what I am asking is if I ground myself each time before I touch the computer innards, can I be sure I have eliminated static electricity because I don't hear or feel anything? IOW, can static electricity flow from me to a metal computer innard without my knowing it? While I am simply standing there holding onto a metal computer part? If you think this is a dumb question - just ignore it. Thanks |
#5
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Thanks all |
#6
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In article ,
geezer wrote: Is static electricity always accompanied by an audible (even if slightly) spark (arc)? I guess what I am asking is if I ground myself each time before I touch the computer innards, can I be sure I have eliminated static electricity because I don't hear or feel anything? IOW, can static electricity flow from me to a metal computer innard without my knowing it? While I am simply standing there holding onto a metal computer part? If you think this is a dumb question - just ignore it. Not a dumb question... the details can be a bit surprising and counterintuitive. The typical static charge that you get zapped by (i.e. that you notice) is in the thousands of volts, sometimes tens of thousands. Under dry conditions and with the right carpet, an evil pair of shoes, and malicious intent, you can build up a charge of 50,000 V for maximum shock infliction on an unsuspecting human. I suggest using a housekey as your contact point if you don't want to suffer the shock yourself. Not that I'd know anything about this first-hand, really I'm a nice guy... The threshold for feeling static shock is about 2,500 V, while it only takes around 400 V to fry electronics. This is a pretty big margin of "dangerous" static shock that can sneak under your radar. Similarly, you can't depend on seeing or hearing the shock if you're not working in a dark and quiet room. So the answer to your question is, no, you cannot depend on your senses to alert you to static shock hazards to electronics. For the most part you can get away with just a few precautions for working on computers -- don't wear sweaters, fleeces, anything wool, or anything else that is obviously static-prone, and don't do computer work on a carpet. If your chair is cloth, don't scootch around in it while working, or better yet, don't use it at all, or treat it liberally with anti-static spray. Ground yourself to the equipment by touching the metal case or power supply before contacting electronics. Some manuals (mostly big-iron equipment like Sun, HP, IBM) demand keeping the power cords connected at all times in order to ground the chassis while working on it, but other manuals make the opposite demand in order to ensure there is no power. Of course, the safest solution is to use a grounding-strap at all times, connecting your wrist to the computer chassis... but frankly, for PC work, I've never seen anyone bother. Even for big-iron equipment, this precaution seems to vary depending on the value of the boards being thrown around. Just some PCI NIC's or such? Bah... But if it's a system board worth more than the average Ferrari? Well then, strap yourself in. Years ago I had an interesting problem at a small office where I was sysadmin/netadmin/PC support... we had just bought a couple of cisco Catalyst 2950G ethernet switches to tie the whole office together, and this was a major purchase for a small company like this. Soon after installation, however, I was losing about one port a week, completely dead. The damage worked out to about $400/port as I recall. Most of the incidents were associated with one particular employee who used a laptop and re-plugged his ethernet cable every morning. After much guessing, cable swapping, and equipment juggling, we finally figured out that the problem was static discharge -- the whole office was carpeted, and this employee was unknowingly zapping the end of the ethernet cable when he grabbed it every morning to plug it in. Given the 400-2500 V "danger zone" of unfeelable static shocks, this is understandable, but I was surprised at how fragile the cisco ports were. The solution was a hack, but it worked: Spray the entire carpeting of the office with 5:1 water / fabric softener solution (re-applied a few times a year, a pain) and inform laptop users to avoid touching the metal pins on the ethernet cables. With today's technology, of course, wireless is a better solution for the laptop workers. Hope that helps, -SK |
#7
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Steve Kives wrote:
.... snip ... The typical static charge that you get zapped by (i.e. that you notice) is in the thousands of volts, sometimes tens of thousands. Under dry conditions and with the right carpet, an evil pair of shoes, and malicious intent, you can build up a charge of 50,000 V for maximum shock infliction on an unsuspecting human. I suggest using a housekey as your contact point if you don't want to suffer the shock yourself. Not that I'd know anything about this first-hand, really I'm a nice guy... In the third grade the routine was to squirm about in your seat, getting the seat of your pants all shiny, and then zap the ear of the person (preferably girl) sitting in front of you. Then look innocent. -- "If you want to post a followup via groups.google.com, don't use the broken "Reply" link at the bottom of the article. Click on "show options" at the top of the article, then click on the "Reply" at the bottom of the article headers." - Keith Thompson |
#8
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Newer car tires are not using carbon black that makes the
tires sufficiently conductive. So when I exited a car while carrying a radio, the AC power cord first dropped to earth. I was touching the antenna lead. Electricity went from car, through me, into antenna connector, through radio, down power cord to earth. A complete electric circuit existed through electronics - the prerequisite for damage. AM/FM front end converter chip was damaged. I did not feel that shock. But every other time, the static electric generated shock existed. Electronic damage occurred the one time I did not feel a discharge. No, its not a dumb question. Also note another requirement for damage. First a complete electric circuit must exist. First there must be a path into and one out of the electronics - else no damage. This principle is important because it explains why electronics can be routinely zapped and not suffer damage. Not understanding this principle is why so many create myths about damage from static electric discharges. geezer wrote: Is static electricity always accompanied by an audible (even if slightly) spark (arc)? I guess what I am asking is if I ground myself each time before I touch the computer innards, can I be sure I have eliminated static electricity because I don't hear or feel anything? IOW, can static electricity flow from me to a metal computer innard without my knowing it? While I am simply standing there holding onto a metal computer part? If you think this is a dumb question - just ignore it. Thanks |
#9
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"w_tom" wrote in message ... Newer car tires are not using carbon black that makes the tires sufficiently conductive. So when I exited a car while carrying a radio, the AC power cord first dropped to earth. I was touching the antenna lead. Electricity went from car, through me, into antenna connector, through radio, down power cord to earth. A complete electric circuit existed through electronics - the prerequisite for damage. AM/FM front end converter chip was damaged. I did not feel that shock. So how do you know that this damaged the radio? Maybe it broke when you dropped in in the back seat. |
#10
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I traced the discharge circuit that included a damaged AM/FM
front end converter. Got a new chip. Radio worked find. It was working when I took it out to the car. It was not dropped. In 20 years it never failed. It was not working immediately after I arrived. The part that was damaged would have been in the discharge path. And I thought it unusual when I got out of the car that I did not feel the usual electric shock. But did not put 'two and two' together until later - after the damage. Noozer wrote: So how do you know that this damaged the radio? Maybe it broke when you dropped in in the back seat. |
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