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Power Strip Causing Ground Loop?
First, let me tell you that I'm a retard when it comes to electronic
stuff. Anyway... I was fiddling around behind my computer and got a nice shock. I'm trying to figure out this problem and am hoping you folks could help me out. I get the shock when I touch any part of the back of my computer or wires, and also touch the metal part of the cable that comes in and connects to my cable modem. Here's the deal: I live in an older house that is not grounded. The ground prong on the outlets isn't connected to ground or anything else. Also, I've determined that the coax cable coming in to my cable modem is grounded. Somthing seems to be making the ground prong on my outlet hot. I've narrowed down the problem to my power strip. I've unplugged everything from my outlet and I check the outlet for voltage. Neutral to hot gives me 110V. Neutral to ground give me nothing (actually, for some odd reason, there does seem to be a slight voltage (less than 2V). Hot to ground also gives me nothing. As one would expect. Now, if I plug in a power strip and do the same check on one of the outlets on the power strip, I get: neutral to hot 110V, neutral to ground around 60V and hot to ground around 60V. Is this right? I've checked this with two power strips and I get the same results. What would cause this? Is the polarity on my outlet wrong? Or, am I just a dummy and am misintepreting what is going on. This misterious 60V is what give me the shock. Howard |
#3
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Todd H. ) wrote:
: ...your outlet is heinously miswired. Not miswired, just wired 40+ years ago with no ground. Couldn't I just ground the outlet myself? Run a wire from the ground in the outlet to a water pipe outside? Would that solve my problems? Howard |
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Howard Knight wrote:
Todd H. ) wrote: : ...your outlet is heinously miswired. Not miswired, just wired 40+ years ago with no ground. Couldn't I just ground the outlet myself? Run a wire from the ground in the outlet to a water pipe outside? Would that solve my problems? Howard There are electrical codes with which you should comply. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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Howard Knight wrote:
Todd H. ) wrote: : ...your outlet is heinously miswired. Not miswired, just wired 40+ years ago with no ground. Couldn't I just ground the outlet myself? Run a wire from the ground in the outlet to a water pipe outside? Would that solve my problems? Howard, First, I think you should replace that outlet strip. They have MOV's between the hot and ground and neutral and ground. When an MOV gets a big surge, they start leaking current that they would have blocked before the damage. Because your ground is floating, the leakage of the two sets of MOV's has made a voltage divider between hot and neutral with the ground at the midpoint. Grounding the outlet feeding your computer is a good idea, but it may trip breakers or blow fuses if the outlet strip is really hammered. You might think about getting your house wiring brought up to modern configuration, proper grounding and GFI outlets add a lot to the electrical safety of a house. It would probably add to the resale value as well. If you are in a rental house, good luck. Bob |
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On Fri, 10 Jun 2005 21:39:09 +0000, Howard Knight wrote:
First, let me tell you that I'm a retard when it comes to electronic stuff. Anyway... I was fiddling around behind my computer and got a nice shock. I'm trying to figure out this problem and am hoping you folks could help me out. I get the shock when I touch any part of the back of my computer or wires, and also touch the metal part of the cable that comes in and connects to my cable modem. Here's the deal: I live in an older house that is not grounded. The ground prong on the outlets isn't connected to ground or anything else. Then get that fixed by a qualified professional before you burn your house down or kill one of your children. Sorry, Rich |
#7
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On Fri, 10 Jun 2005 23:31:57 +0000, Howard Knight wrote:
Todd H. ) wrote: : ...your outlet is heinously miswired. Not miswired, just wired 40+ years ago with no ground. Couldn't I just ground the outlet myself? Run a wire from the ground in the outlet to a water pipe outside? Would that solve my problems? Use #10 AWG solid bare copper, and if you can't afford to have it done by a qualified professional, at least have it inspected by a qualified professional. Don't murder your children. Good Luck! Rich |
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#9
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On Fri, 10 Jun 2005 21:21:55 -0400 Gary Schafer
wrote: The doom and gloomers sure do come out of the woodwork. Yep, I completely agree. It's rather clear that no one before Gary had much of a clue as to what was really going on here. What you are seeing is the completely normal result of having a home system with no ground, a power strip with surge protection, and a voltmeter with a high imput impedance. You can leave things just the way they are, but the best thing would be to update the house wiring and give yourself some good grounds. In the meantime, your surge protector only gives your computer limited protection. A proper ground is applied at the service entrance (where the AC power enters the house) and follows the wiring out to each outlet from there. An alternate ground can still protect you from electrical shock if it is well done, but it may cause other problems and may not allow your surge limiters to protect your equipment as well. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
#10
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Rather scary that so many know so much as to reply ...
without first learning electrical basics. The wall receptacle safety ground must have a dedicated wire connection to breaker box safety ground. Not to earth; to safety ground. And definitely not a connection to pipes. Wire connection to pipes must be to remove electricity from that pipe. Never make a connection intended to dump electricity into pipes. A worst case scenario, a pipe connection might only electrify a wet human in a shower or bath. Wet is the worst time to touch electricity. Connection to earth ground also does nothing useful. The important connection to earth must be from breaker box only. A receptacle safety ground must connect to breaker box so that a wiring fault does trip the circuit breaker. No way around that grounding (bonding) requirement. The wall receptacle, power strip, or computer need not be miswired to obtain leakage voltage. Without a safety ground, then leakage currents might cause the chassis to 'feel' electrically hot. Not a danger to a dry human. However leakage can cause damage to interconnected computer components and cause other irritating problems. Easiest solution is to have an electrician route a properly earthed wire to that receptacle. Electricians have fancy toys that make 'impossible to route' wires simple. If a receptacle is not safety grounded, then the circuit should be GFCIed. GFCI is a minimum necessary correction. Better power strip is typically about $3+, no nonsense surge protector or filter components inside, AND the power strip must include a 15 amp circuit breaker. The breaker being important for human safety - for reasons not discussed here. Howard Knight wrote: Todd H. ) wrote: : ...your outlet is heinously miswired. Not miswired, just wired 40+ years ago with no ground. Couldn't I just ground the outlet myself? Run a wire from the ground in the outlet to a water pipe outside? Would that solve my problems? Howard |
#11
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-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "Todd H." ?????? ??? ?????? ... (Howard Knight) writes: I get the shock when I touch any part of the back of my computer or wires, and also touch the metal part of the cable that comes in and connects to my cable modem. Here's the deal: I live in an older house that is not grounded. The ground prong on the outlets isn't connected to ground or anything else. Red flag. This is problem #1. This isn't a ground loop. This is an absence of ground. The former is an inconvenience, the latter can kill ya. Is this legal in USA?Here, there are people who put shucko-plugs in old fashioned three-prong receptacles, with the result, abcence of ground (the appliance works, but is not grounded).Modern computers that work in the GHz range need very good grounding, because their case becomes hot otherwise from induced high-frequency currents. Also, I've determined that the coax cable coming in to my cable modem is grounded. Typically staked at the junction box by the cable company. Somthing seems to be making the ground prong on my outlet hot. I've narrowed down the problem to my power strip. I've unplugged everything from my outlet and I check the outlet for voltage. Neutral to hot gives me 110V. Neutral to ground give me nothing (actually, for some odd reason, there does seem to be a slight voltage (less than 2V). The odd reason is that if we believe what you're telling us (i.e. that your ground on your outlet is completely floating) I'd believe any voltage you'd tell me between ground and the neutral of the outlet. In my house:hot to neutral and hot to ground 225 volts (3:10 pm)and, of course, neutral to ground 0 volts.I have checked every inch of the installation myself, because I think that electricity is quite a good friend,but canbecome dangerous sometimes. Hot to ground also gives me nothing. As one would expect. As one would expect in Danger World where ground is left completely floating. :-) In the Safe World, neutral and ground should be the same potential with 0V, and hot to ground should measure in the 110-120V range. Notice however that neutral even having a potential of 0 volts is run by large enough currents to cause problems in bad installations (neutral bars in distribution panels and neutrals in electric ranges e.g. tend to burn to be charcoaled completely). Now, if I plug in a power strip and do the same check on one of the outlets on the power strip, I get: neutral to hot 110V, Good. Neutral to ground around 60V Wee! This is a Big Problem. and hot to ground around 60V. Is this right? Oy. No. You gotta remember here, your ground in your outlets is completely floating, and someone should tell you this is Very Bad. I've checked this with two power strips and I get the same results. What would cause this? Is the polarity on my outlet wrong? Or, am I just a dummy and am misintepreting what is going on. This misterious 60V is what give me the shock. Call an electrician. Today. You've got potentially lethal problems with your home's electric wiring. You may also have some power strips in need of replacement. 60V on your third wire ground is Not Good (tm). Since your computer is a metal enclosed 3-wire appliance, it's presenting allcomers with 60V ready to shock the crap out of em. Most aren't aware that surge suppressing power strips do nothing without a real third wire ground, and it appears that they might also be creating a rather hazardous situation. I suspect that these may be surge suppressing power strips with some circuitry that is potentially faulty (burned out MOV's for instance) and is therefore creating a more hazardous situation than you have at your outlet to begin with because your outlet is heinously miswired. Don't take offense, but do call an electrician. Best Regards, -- /"\ ASCII Ribbon Campaign | Todd H \ / | http://www.toddh.net/ X Promoting good netiquette | http://triplethreatband.com/ / \ http://www.toddh.net/netiquette/ | "4 lines suffice." |
#12
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Dimitrios Tzortzakakis wrote:
Is this legal in USA?Here, there are people who put shucko-plugs in old fashioned three-prong receptacles, with the result, abcence of ground (the appliance works, but is not grounded).Modern computers that work in the GHz range need very good grounding, because their case becomes hot otherwise from induced high-frequency currents. Bull****. The potential at the case is power leaked in the psu, not _any_ other parts in the computer. The psu has a filter on the input, which leaks tiny currents to ground/chassis. This has nothing to do with the cpu or any other thing. It has nothing to do with induction afaik. -- MVH, Vidar www.bitsex.net |
#13
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"Howard Knight" wrote in message
... I live in an older house that is not grounded. The ground prong on the outlets isn't connected to ground or anything else. if you want to carry on living i sugest you get this problem rectified imediatly. if you were living in the UK the wiring would be condemed by the power company as soon as they were aware of it. Colin. |
#14
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Jim Adney wrote:
On Fri, 10 Jun 2005 21:21:55 -0400 Gary Schafer wrote: The doom and gloomers sure do come out of the woodwork. Yep, I completely agree. It's rather clear that no one before Gary had much of a clue as to what was really going on here. What you are seeing is the completely normal result of having a home system with no ground, a power strip with surge protection, and a voltmeter with a high imput impedance. But ... that combination can be deadly. If you don't believe me, google "guitar amp death caps." You can leave things just the way they are, but the best thing would be to update the house wiring and give yourself some good grounds. In the meantime, your surge protector only gives your computer limited protection. A proper ground is applied at the service entrance (where the AC power enters the house) and follows the wiring out to each outlet from there. An alternate ground can still protect you from electrical shock if it is well done, but it may cause other problems and may not allow your surge limiters to protect your equipment as well. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
#15
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w_tom wrote:
Rather scary that so many know so much as to reply ... without first learning electrical basics. Oh, gawd. He's invaded yet another group. |
#16
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On Fri, 10 Jun 2005 23:51:39 -0500, Jim Adney
wrote: It's rather clear that no one before Gary had much of a clue as to what was really going on here... You can leave things just the way they are.... Speaking of clues: if the OP leaves things "just the way they are," he will have an ever-present and very real 60V potential between his computer case and the cable shield. That's 60Vrms at 60Hz between bare, exposed metal conductors possibly just inches apart. Dunno about you, but I wouldn't want that. |
#17
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On Sat, 11 Jun 2005 12:31:18 -0700, Al Brenan
wrote: It's rather clear that no one before Gary had much of a clue as to what was really going on here... You can leave things just the way they are.... Speaking of clues: if the OP leaves things "just the way they are," he will have an ever-present and very real 60V potential between his computer case and the cable shield. That's 60Vrms at 60Hz between bare, exposed metal conductors possibly just inches apart. Dunno about you, but I wouldn't want that. http://users.tkk.fi/~then/mytexts/ungrounded_pc.html |
#18
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On Fri, 10 Jun 2005 23:31:57 -0000,
(Howard Knight) wrote: Todd H. ) wrote: : ...your outlet is heinously miswired. Not miswired, just wired 40+ years ago with no ground. Couldn't I just ground the outlet myself? Run a wire from the ground in the outlet to a water pipe outside? Would that solve my problems? Howard If you have a un-grounded U-Ground outlet installed in a 2 wire UN-GROUNDED box, this is a violation of most US electrical codes. You need to replace 2 prong outlets wit 2 prong outlets UNLESS there is a ground wire attached to the 1)box, 2)the green terminal on the outlet. Many bathroom outlet and light fixture boxes were required to have a separate (bare) ground wire connected to the cold water piping. This is fine until the addition of Di-electric union or plastic piping from the water supply. If your electric service does not have a ground rod driven into the earth, have this added to the required cold water ground bond wire at the service entrance. , _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org |
#19
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On Sat, 11 Jun 2005 02:43:59 -0400, w_tom wrote:
The wall receptacle safety ground must have a dedicated wire connection to breaker box safety ground. Not to earth; to safety ground. And definitely not a connection to pipes. MODERN rules. Old rules DID require COLD WATER PIPES, but *never* GAS pipes. , _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org |
#20
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Vidar Løkken wrote:
Bull****. The potential at the case is power leaked in the psu, not _any_ other parts in the computer. The psu has a filter on the input, which leaks tiny currents to ground/chassis. This has nothing to do with the cpu or any other thing. It has nothing to do with induction afaik. Just for fun I measured those values on a atx psu connected to a 100W load, trough a insulation xfmr. I measured 60-65V, and 70µA. This current is so tiny you won't normally feel it, so no danger to human beings. However, if some equipment is earthed, and some not, it might destroy electronics. Also note that this was in a 220V IT circuit, which means that earth is nominally floating. -- MVH, Vidar www.bitsex.net |
#21
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Jim Adney writes:
On Fri, 10 Jun 2005 21:21:55 -0400 Gary Schafer wrote: The doom and gloomers sure do come out of the woodwork. Yep, I completely agree. It's rather clear that no one before Gary had much of a clue as to what was really going on here. What you are seeing is the completely normal result of having a home system with no ground, a power strip with surge protection, and a voltmeter with a high imput impedance. You can leave things just the way they are, .....if of course one enjoys the safety and thrill of getting shocked by your computer case. :-) The situation may be relatively common, but it's far from normal or safe. The only responsible solution to the OP's quandry is an electrician, plain and simple. Then again, what would I know about electricity? Best Regards, -- /"\ ASCII Ribbon Campaign | Todd H \ / | http://www.toddh.net/ X Promoting good netiquette | http://triplethreatband.com/ / \ http://www.toddh.net/netiquette/ | "4 lines suffice." |
#22
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Vidar Løkken wrote:
Vidar Løkken wrote: Bull****. The potential at the case is power leaked in the psu, not _any_ other parts in the computer. The psu has a filter on the input, which leaks tiny currents to ground/chassis. This has nothing to do with the cpu or any other thing. It has nothing to do with induction afaik. Just for fun I measured those values on a atx psu connected to a 100W load, trough a insulation xfmr. I measured 60-65V, and 70µA. This current is so tiny you won't normally feel it, so no danger to human beings. You might be shocked (pun intended) to learn that capacitors (and other components) sometimes fail. However, if some equipment is earthed, and some not, it might destroy electronics. Also note that this was in a 220V IT circuit, which means that earth is nominally floating. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
#23
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On Sat, 11 Jun 2005 12:31:18 -0700 Al Brenan
wrote: On Fri, 10 Jun 2005 23:51:39 -0500, Jim Adney wrote: It's rather clear that no one before Gary had much of a clue as to what was really going on here... You can leave things just the way they are.... Speaking of clues: if the OP leaves things "just the way they are," he will have an ever-present and very real 60V potential between his computer case and the cable shield. That's 60Vrms at 60Hz between bare, exposed metal conductors possibly just inches apart. Dunno about you, but I wouldn't want that. Sure, it's 60V as seen on a 10 MOhm meter, but the source impedance is on the order of a MegOhm. That's never going to provide enough current to be dangerous. Of course that assumes that all his components remain in good condition. If something actually fails, then you're right and he is without a safety ground. He could experiment with this by touching both "grounds" at the same time and measuring the voltage on his PC chassis at the same time. He'll discover that he has grounded the PC and that there is no longer a voltage there. He's already explained that he gets a shock whenever he touches both parts. I believe him. The fact that he's done this several times with no extreme effects implies that it's a perceptable amount of current, but not a dangerous one. This is what one would expect from a power strip with surge protection that lacked a ground. He could probably improve his situation by just grounding his PC to the cable shield. This carries the possiblity of passing a shock on to someone working on the cable system, however, so that's why I really don't recommend it. And I agree, we would ALL be better off with all grounded outlets, but there are many old houses around which just don't have them. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
#24
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If that happens, then why does not my GFCI breaker trip?
-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "Vidar Løkken" ?????? ??? ?????? ... Dimitrios Tzortzakakis wrote: Is this legal in USA?Here, there are people who put shucko-plugs in old fashioned three-prong receptacles, with the result, abcence of ground (the appliance works, but is not grounded).Modern computers that work in the GHz range need very good grounding, because their case becomes hot otherwise from induced high-frequency currents. Bull****. The potential at the case is power leaked in the psu, not _any_ other parts in the computer. The psu has a filter on the input, which leaks tiny currents to ground/chassis. This has nothing to do with the cpu or any other thing. It has nothing to do with induction afaik. -- MVH, Vidar www.bitsex.net |
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Then why is a computer in a fully enclosure metal case?Provided, that a
computer works with voltages not higher than 12 volt, and the PSU is already shielded, why not put it in a plastic case? -- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "Vidar Løkken" ?????? ??? ?????? ... Vidar Løkken wrote: Bull****. The potential at the case is power leaked in the psu, not _any_ other parts in the computer. The psu has a filter on the input, which leaks tiny currents to ground/chassis. This has nothing to do with the cpu or any other thing. It has nothing to do with induction afaik. Just for fun I measured those values on a atx psu connected to a 100W load, trough a insulation xfmr. I measured 60-65V, and 70µA. This current is so tiny you won't normally feel it, so no danger to human beings. However, if some equipment is earthed, and some not, it might destroy electronics. Also note that this was in a 220V IT circuit, which means that earth is nominally floating. -- MVH, Vidar www.bitsex.net |
#26
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Vidar Løkken wrote:
Vidar Løkken wrote: Bull****. The potential at the case is power leaked in the psu, not _any_ other parts in the computer. The psu has a filter on the input, which leaks tiny currents to ground/chassis. This has nothing to do with the cpu or any other thing. It has nothing to do with induction afaik. Just for fun I measured those values on a atx psu connected to a 100W load, trough a insulation xfmr. I measured 60-65V, and 70µA. This current is so tiny you won't normally feel it, so no danger to human beings. However, if some equipment is earthed, and some not, it might destroy electronics. According to several references, GFCI designed for personnel protection will trip when leakage current exceeds 5 milliamps. |
#27
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Dimitrios Tzortzakakis wrote:
Then why is a computer in a fully enclosure metal case? Because its pretty hard to make a computer double insulated. Provided, that a computer works with voltages not higher than 12 volt, and the PSU is already shielded, why not put it in a plastic case? See laptops - computers that have voltages 20 volts entering their cases and have plastic cases. |
#28
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Dimitrios Tzortzakakis wrote:
Then why is a computer in a fully enclosure metal case?Provided, that a computer works with voltages not higher than 12 volt, and the PSU is already shielded, why not put it in a plastic case? Because of RF emissions. It can/will make inteference with other electronic equipment, but it is not the RF that induces the voltage. Besides, notebooks is plastic cabinets... And so is the plexiglass cabinets that is commonplace those days. But you require a common ground, and so metal is practical, in favour of running a ground cable to every device. Also metal is more durable than plastics. But yes, a computer emits _huge_ mengths of RF, enough to disturb a radio, but not enough to induce 60V in the chassis. Maybe a few µV. -- MVH, Vidar www.bitsex.net |
#29
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Arny Krueger wrote:
Dimitrios Tzortzakakis wrote: Then why is a computer in a fully enclosure metal case? Because its pretty hard to make a computer double insulated. No, not really. The 12V is 12V from ground. Not some 1xx volts from ground, so it'd not have to be double insulated. The PSU would have to be, and that would be pretty easy. Provided, that a computer works with voltages not higher than 12 volt, and the PSU is already shielded, why not put it in a plastic case? See laptops - computers that have voltages 20 volts entering their cases and have plastic cases. And doubly so because the PSU leakage is capacitors connected to gnd/midpoint _on purpose_. Yes bad habit, replying to post and posts child. -- MVH, Vidar www.bitsex.net |
#30
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On Mon, 13 Jun 2005 14:57:40 +0300, "Dimitrios Tzortzakakis"
wrote: Then why is a computer in a fully enclosure metal case?Provided, that a computer works with voltages not higher than 12 volt, and the PSU is already shielded, why not put it in a plastic case? To provied FCC (and other regulatory) EMI shielding. Many of those plastilc looking cases are either coated or contain carbon or other conductive material. See FCC rules, Part 15 , _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org |
#31
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Arny Krueger wrote:
According to several references, GFCI designed for personnel protection will trip when leakage current exceeds 5 milliamps. Yep, which is _far_ from 70µA. But in Norway, the norm is 30mA. However, Norway has a IT-net, not a TN-net. (Or was it TT? Never remember the difference :P) -- MVH, Vidar www.bitsex.net |
#32
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On Mon, 13 Jun 2005 14:54:01 +0300, "Dimitrios Tzortzakakis"
wrote: If that happens, then why does not my GFCI breaker trip? -- 1) the leakage current is below the GFIC trip threshold (this is likely, as the threshold would be set to prevent 'nuisance trips) 2) the GFIC breaker is defective or improperly installed. 3) You are not plugged into the circuit protected by the GFIC breaker , _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org |
#33
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Vidar Løkken wrote:
Arny Krueger wrote: According to several references, GFCI designed for personnel protection will trip when leakage current exceeds 5 milliamps. Yep, which is _far_ from 70µA. But in Norway, the norm is 30mA. In the US - we consider 30 ma to be the limit for protecting equipment. The threshold for protecting personel is 5 ma. |
#34
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Arny Krueger wrote:
Yep, which is _far_ from 70µA. But in Norway, the norm is 30mA. In the US - we consider 30 ma to be the limit for protecting equipment. The threshold for protecting personel is 5 ma. Yep, which relates back to that in a IT-net you have insulation between the midpoint in xmfr and gnd, that also limits the current, while in the US you have a TN net where gnd is connected straight to the mid-point. Don't ask me to explain the differences, I only know that the norwegian system is considdered safer, and there's two countries that is using it. Norway and Peru or something like that. So we have 2 wires, with a potential to each other of 220V, both being "hot" relative to gnd. Perphaps someone else in here can explain the difference between a IT and a TN/TT net? -- MVH, Vidar www.bitsex.net |
#35
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Vidar Løkken wrote:
Arny Krueger wrote: Yep, which is _far_ from 70µA. But in Norway, the norm is 30mA. In the US - we consider 30 ma to be the limit for protecting equipment. The threshold for protecting personel is 5 ma. Yep, which relates back to that in a IT-net you have insulation between the midpoint in xmfr and gnd, that also limits the current, while in the US you have a TN net where gnd is connected straight to the mid-point. See reference, below. Don't ask me to explain the differences, I only know that the norwegian system is considdered safer, and there's two countries that is using it. Norway and Peru or something like that. So we have 2 wires, with a potential to each other of 220V, both being "hot" relative to gnd. Perphaps someone else in here can explain the difference between a IT and a TN/TT net? http://www.mikeholt.com/documents/mo...gworldwide.pdf pp 7-8 |
#36
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Arny Krueger wrote:
http://www.mikeholt.com/documents/mo...gworldwide.pdf Thanks a lot That was a quite informative pdf, actually I should've remembered my electrical installations book was 2 meter from me... Thought I'd sold that book after last year, but anyway, that PDF described it better than the book! pp 7-8 I had a peek at the rest... -- MVH, Vidar www.bitsex.net |
#37
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On Sun, 12 Jun 2005 21:33:53 -0500, Jim Adney
wrote: Sure, it's 60V as seen on a 10 MOhm meter, but the source impedance is on the order of a MegOhm. That's never going to provide enough current to be dangerous. Of course that assumes that all his components remain in good condition. If something actually fails, then you're right and he is without a safety ground. Right on both points. It's that pesky second point that bothers me. In addition, that small but probably continuous current could be damaging to sensitive components; remember we're dealing with a computer and a cable modem here, lots of low voltage, low current, high speed "stuff" that could be damaged by strong transients. An interesting but flawed solution is to connect the power strip "ground" to the shield of the modem. That would give the strip a return reference, but one fraught with difficulty on a number of levels - power currents injected into an RF shield being the most conspicuous. I don't like it. I'd get an electrician. -- Al Brennan "If you only knew the magnificence of the 3, 6 and 9, then you would have a key to the universe." Nicola Tesla |
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-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "Steve Urbach" ?????? ??? ?????? ... On Mon, 13 Jun 2005 14:54:01 +0300, "Dimitrios Tzortzakakis" wrote: If that happens, then why does not my GFCI breaker trip? -- 1) the leakage current is below the GFIC trip threshold (this is likely, as the threshold would be set to prevent 'nuisance trips) The threshold in europe is always 30 mA. 2) the GFIC breaker is defective or improperly installed. It's a new Siemens GFCI breaker I installed myself, and I hope I can install one correctly. 3) You are not plugged into the circuit protected by the GFIC breaker , _ The breaker protects my whole house. , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org |
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On Tue, 14 Jun 2005 14:55:33 +0300, "Dimitrios Tzortzakakis"
wrote: The breaker protects my whole house. Ah! the difference between international systems. The US residential mainly requires only certain Branch circuits to be GFIC (and now ARC fault) protected. Newer 'Industrial' systems have the "whole" service panel version. , _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org |
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Get an outlet tester. They plug into the outlet and let you know if it is
wired correctly. I believe you will find that you have an outlet with the neutral and hot reversed. How is your internet connection? In my experience this can cause wicked packet loss. "Howard Knight" wrote in message ... First, let me tell you that I'm a retard when it comes to electronic stuff. Anyway... I was fiddling around behind my computer and got a nice shock. I'm trying to figure out this problem and am hoping you folks could help me out. I get the shock when I touch any part of the back of my computer or wires, and also touch the metal part of the cable that comes in and connects to my cable modem. Here's the deal: I live in an older house that is not grounded. The ground prong on the outlets isn't connected to ground or anything else. Also, I've determined that the coax cable coming in to my cable modem is grounded. Somthing seems to be making the ground prong on my outlet hot. I've narrowed down the problem to my power strip. I've unplugged everything from my outlet and I check the outlet for voltage. Neutral to hot gives me 110V. Neutral to ground give me nothing (actually, for some odd reason, there does seem to be a slight voltage (less than 2V). Hot to ground also gives me nothing. As one would expect. Now, if I plug in a power strip and do the same check on one of the outlets on the power strip, I get: neutral to hot 110V, neutral to ground around 60V and hot to ground around 60V. Is this right? I've checked this with two power strips and I get the same results. What would cause this? Is the polarity on my outlet wrong? Or, am I just a dummy and am misintepreting what is going on. This misterious 60V is what give me the shock. Howard |
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