The Shocking Truth About ESD - Comments Page 1
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The year was 1983. I was the sole programmer on a micro computer for a large company. I had 2 machines with one chair and a carpeted floor. |
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"Do not attach a wire to your computer’s chassis and then attach the other end to the grounding wire of an electrical outlet, a solution that seems obvious but is actually quite dangerous." It seems to me that many of my computers use grounded (3 wire) plugs that already connect my computer to the ground in my electrical outlet. |
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In regards to "repair workers often wear wristbands that keep them constantly grounded via a wire attached to a nearby electron" |
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Bob, |
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Thanks for these shocking tidbits, Bob. I actually learned some useful things from the video guy. ... Stuff I didn't know. Mac |
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Bob, |
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Thanks for a short, but comprehensive and easily understandable explanation of ESD. Jan |
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Having worked as an Electrician for several years I know for a fact that this statement is false "Do not attach a wire to your computer’s chassis and then attach the other end to the grounding wire of an electrical outlet, a solution that seems obvious but is actually quite dangerous." any computer that has a third grounding lug on its cord does exactly this! That grounding lug is connected straight to the case inside the computer. |
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What you didn't mention is that the extra dry conditions here in the West, due to lack of rain has created a condition that is more conducive to static discharges. And by the way you can tell that the humidity is low by your nose. And because my nose unusually large I have a distinct advantage over others. I am that no one will be envious. |
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I have encountered problems with computers related to the sudden zap of ESD - lost data and sudden blue or black screens. My solution was to place a grounding strip (similar to the wrist band) at the spot under the ledge of my desk where I grab it to pull my chair into position when I first sit down. This strip is just connected to the heat ducting of my furnace system. This automatically removes my charge painlessly and has protected my computers for many years now. |
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Thanks Bob, for that very thorough and informative |
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Don’t try to go to the plumbing store for an electron sink. Sink here refers to a ground, typically an “earth” ground with a resistor in series leading to a banana jack mounted near your test station. You connect the wrist strap to yourself, and plug the banana plug into the ground sink. To do the job right, you should have a tester to make sure that you are properly connected. You plug the banana jack into the tester, and touch a test point on the tester. If you are connected properly the tester will signal an ok, usually audible and visual. If not, there are conductive lotions that can be rubbed on your wrist to aid the connection. This was a necessity on several dry days. A proper workstation would also have an ESD mat connected to the ground sink, usually with a banana plug for your wrist strap cable. In an industry setting a special grounded floor and heel straps can serve the same purpose, but still need testing to make sure that they are actually grounding. Note that an untested wrist strap can be worthless. I once worked in a lab with over 20 other software engineers that were performing embedded work that included plugging memory chips into boards and boards into chassis, and emulators into CPU sockets after removing the CPUs. There were a handful of wrist straps floating around the lab, and ground sinks installed every 6 feet or so. I decided to test one, then all of the straps. The majority were open circuits, only two were functioning. That probably explains why some equipment was failing and PROMS that would no longer program. Quickly ordered enough for everyone that handled boards to have a wrist strap and cord and a few extras for the lab and provided instructions on testing at least daily. (Should be tested after attaching to your self before using, and retesting if removed and re attached, e.g. after lunch.) Unless they found another testing station, I don’t think anyone else bothered to test unless I said something as there were few entries from the software team in the log. If you don’t have a proper setup, the poor man alternative is to grab an exposed part of a metal chassis that you will be working on. Grab it constantly or at least frequently so that you are at the same potential as the equipment that you are working on. If a board or other equipment needs to be removed, use an antistatic ESD bag for boards (save some for reuse); antistatic foam or tubes for chips. Grab the storage container while grounded before moving equipment. Putting bare equipment particularly chips and boards, on a table or desk, particularly on papers, is a recipe for needing replacements. As an aside. I used to work on stage crew in high school. We would form a chain of 3 or 4 people, shuffle our feed on the carpet, then take a key and touch a metal object. We could get sparks over an inch long. (They really hurt without the key.) |
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Re Troy 20 Apr 15 "...I know for a fact that this statement is false "Do not attach a wire to your computer’s chassis and then attach the other end to the grounding wire of an electrical outlet, a solution that seems obvious but is actually quite dangerous." any computer that has a third grounding lug on its cord does exactly this! That grounding lug is connected straight to the case inside the computer." In my early years I worked for an advanced research lab. The grounded chassis were a problem with ground loop currents, probably because there were several electrical panels that controlled the many outlets in the lab. Each ground plug had to be removed and the chassis connected to a common earth ground buried in the parking lot. If the chassis is already grounded through the cord, don't connect another ground to the chassis. |
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I can recall when small electronic PBXs became popular we ended up replacing many of them until the technicians learned to properly use antistatic straps before taking off the cover to work on the insides of them. We even had training courses for techs to attend to learn about the damage ESD can cause, damage that might not even be apparent until much later. |
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With regards to "repair workers often wear wristbands that keep them constantly grounded via a wire attached to a nearby electron sink", and the comment posted by Mike: The idea of a low-resistance connection between the worker and the machine frame (i.e. the frame that is connected to ground when the machine is plugged in), is to eliminate the voltage potential between the worker and the machine. If there is no voltage potential between them, then there can be no electrostatic discharge in either direction. The statement "No one should ground themselves while working around any electrical equipment unless they are using a wrist band specifically designed for this purpose" is also somewhat unclear. You must ground to the same ground as the equipment, otherwise you risk creating a phenomenon known as ground current. Basically it means that two different places on earth, even a few yards apart, are at different voltage potentials and are constantly changing as per ambient conditions, thus generating current through the circuit which passes through the person and the equipment. Last but not least, some equipment uses a configuration known as a "Faraday cage", where the machine frame and case are actually electrified at a low voltage so as to prevent electrons and other particles from entering the space within the machine. This is more prevalent on main frames, and the wrist band must be used when working on the internals of such machines so as to eliminate voltage potentials. Why don't birds get electrocuted on high wires? They just aren't grounded! Cheers |
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For Troy and Mike...I read this as a caution against using a jury-rigged grounding solution instead of the wrist-strap/sink mechanism mentioned. I think it's assumed if you've got your computer case open and are working on the components inside, you usually (I know, "not always!") have it unplugged. I heard somewhere that having an electronic device plugged in still doesn't provide adequate protection against ESD if you're working on the innards...anyone with more electrical knowledge have anything to say? A note also: this is why many gas pumps have a caution against using cell phones while dispensing gas and why you shouldn't get into your car while gas is dispensing and then back out to put the nozzle back...you can theoretically generate enough ESD to ignite the fuel vapor. |
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Too bad, I am envious. |
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thanks Bob for reminding me about shuffling around on a shag rug, and then touching my finger to a friend's earlobe. we did that as kids, and rubbing the balloon and putting it "magically" on the wall. thanks for the sweet memories. |
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FYI, it's not just computers. While dusting my TV, I got a static electricity shock and in the process fried the power switch. The TV was never able to be turned on again. |
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I had an ipod Touch for a couple years and I had 6 electrical shock incidents that I never could figure out and I am not sure that anyone I told ever believed me. They have knocked the ipod out of my hand and the earbuds out of my ears and the jolt in my ears and head every time was awful. There was never anything consistant...I was inside, outside, on cement, on grass, different earbuds, different clothes, sometimes it was in my hand and sometimes in my pocket or purse. The only constants were the iTouch and that I have a pacemaker. Doctors couldn't believe the pacemaker had anything to do with it. I lost the iTouch last year and replaced it in October with a Samsung Galaxy. I have used both earbuds and Bluetooth headphones with it and have not had an shock incident so far. I would be interested to know if anyone else has had a problem with a mobile device. |
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