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Thread: shocking

  1. #1

    Exclamation shocking

    my computer is emitting a low-level electrical discharge through the back of the computer. If you touch the screws that hold the case to the tower, a slight "shock" is felt. I just installed DSL and am wondering if that might have anything to do with it. Also, I replaced the power supply 2 months ago, but havn't noticed this before. If anyone has had this problem, or know what might be causing it, please let me know what I need to do to fix it.

    gracias,

    stephen

  2. #2
    You need to unplug your computer before you take the panels off or mess around with the back of it.
    However, I'm curious about this too. All three of my ATX systems do this as well, even when the ATX power switch on the back is off. I assumed it was a grounding problem with the local electricity here. All electrical outlets here have only the 2 holes, no ground.

  3. #3
    Join Date
    Jul 2002
    Location
    Minn
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    17,373
    I am no electronics whiz, but it sounds like both of you have a short in your systems. I would be very cautious about messing around with these systems even with them unplugged.

    laxkid1, it is possible that you caused a short when you installed your DSL or your power supply.

    Malcore, you may want to think about grounding your systems yourself. I believe you can attach a wire to any metal on the computer and to a ground to do this. However, I don't think they should be generating a charge just because they are not grounded, so watch out.

    What do the electronics wizards have to say??

    Budfred

  4. #4
    Join Date
    Nov 2000
    Location
    The Mountain State
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    23,359
    If you don't get this problem with the DSL modem disconnected then the short could be in the phone lines.
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    “When men yield up the privilege of thinking, the last shadow of liberty quits the horizon.” - Thomas Paine
    Remember: Amateurs built the ark; professionals built the Titantic."

  5. #5

    Correction

    Actually, I don't get a shock if I just touch the screws on the back. I DO get a little prick of one if my other hand is on the case and I touch the screws. So small it's hardly noticeable.

    They are properly grounded already, but thanks Budfred.

  6. #6
    Join Date
    Feb 2002
    Location
    Nor'East USA
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    5,505
    Bud,
    This isn't an electronic but merely an electrical problem.

    Malcore,
    Are the blades on your 2 wires the same width in that you can plug them in either way? Here in the US, one is wider to prevent the hot lead from being attached to anything you can touch and causing an electrical shock to your person. (Fire hazards too) If possible try the plug flipped the other way. What voltage is standard where you are? We are on 120V systems and the only other country I know is Britain with 220V.

    Laxkid,
    Same question as I know not where you're from.

    Both,
    Are these screws connected to the case? If they are, current picks the path of least resistance and I'm surprised you can even feel any current by touching the case and the screws.

    Do you have a voltmeter or VOM at your disposal? If the electrical supply in Taiwan is not grounded, I would make a devoted 3wire surge protected outlet(s) for my computers. The neccessary parts are easily found in any 'mart' and half the corner stores around here as well as electrical supply stores and Radio Shack's too.

    You will need to find which lead is common with earth ground and which is not. The one with the wide blade is neutral AND is common with earth ground which is also your rounded ground lead. The narrow lead goes to the hot wire.

    Now this problem could lie within your pc's as well and is not neccessarily a problem with your electrical supply. But I refuse to use my pc's in anything other than 3 wire grounded outlets.

    What may be causing the slight voltages is sometimes referred to as a floating (or static) ground where the case is not connected to either of the leads and is sort of statically charged from things like transformers near enough to conduct a field current to your cases. Any coil can cause voltages to appear on nearby metal by 'field' current. Like how electromagnets work in a way if they weren't grounded you'd get lifted if you touched them and ground at the same time. In this case you could just run a ground wire from a screw on your case to a good ground like copper pipes that originate up through the basement or slab so they conduct to earth ground.

    Lots of times the box that the wires are in are already connected to earth ground and you can just connect a 16 (14 is better) guage minimum wire to that instead. Voltmeters needed to do any of these fixes or measurements.

    If any of you are having any unexplained fuzzy video lines, buzzing speakers or things of the sort on your pc's, it could be the problem being improper grounding.

    My curiousity is definitely piqued, please post as you work this out.

    PM is OK too.
    There's no place like 127.0.0.1

  7. #7

    FTT

    Hey, thanks for the reply!

    1. We are on the same voltage as America and Canada. My PSes are set on the back at 115V, the other choice being 220V.
    2. Yes, the outlets will not accept the blades any way. One blade is wider than the other.
    3. No problems with video or sound.
    4. On my P4 system I just recently went to a second surge protector and have my monitor hooked to a separate one than my comp.
    5. I have been trying to duplicate this "pricking", by touching the case and the thumb screws on the back of my case, and I feel nothing now,even when it's running.
    6. A question. I have a surge peotector which is three pronged, but it has one of those orange adapters on the end with two prongs and a small brass or copper loop. Are these effective and should I be running a ground wire from this loop.
    7. Just for interest's sake. When you buy an electrical item here, say a coffee machine, the plug will have a 6 inch wire coming from it with a small loop at the end. Could this be an indication of a general issue within the country's electrical supply regarding grounding?

    Forgive my ignorance, and thanks for letting me prick...er...pick your brain.

    If this is a general grounding issue, I may have to take up your offer and PM you about the dedicated three prong outlet idea.
    Thanks a bunch again.

  8. #8
    Join Date
    Feb 2002
    Location
    Nor'East USA
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    5,505
    Some grounding adapters have a green wire with the 'loop' you refer to on them instead of the copper blade. Either one can be attached to the center screw that holds the cover of the duplex receptacle on. This, in effect "usually" will give you a good ground providing the electrician that wired the boxes made sure to ground the boxes all the way back to whatever is providing an earthen connection.

    The dedicated 3 prong affair would only be neccessary if the outlet boxes are NOT correctly done such as connected to ground. Which would involve you running at least one wire to some point where you could find a good ground source such as copper/brass/steel/galvanized plumbing lines (NOT PVC or other plastic) or even a lightning rod that's driven into the lawn. This in turn would connect to the ground lead or copper blade you refer to.

    Feeling an electrical discharge on a case or screw is a definite matter for concern so if you relocate any of your pc's and it happens again you will need to find out why.

    BTW, You're welcome. Glad to be of assistance.
    There's no place like 127.0.0.1

  9. #9

    Update

    FTT,

    I had a colleague of mine from the university (elictrical engineer) come in and do the devoted three wire surge protected deal in my home ( cost me a few pi-jios [Taiwan Beer]), just to feel more comfortable. No more shocks or pricks.

    On my third system, I was having other problems, HDD shutting on and off. I suspected the PS was too small (300W) for what I was running. Upgraded that to a 350W ( Enermax! AUGHHH, I know, I know....all I can get here except dirt cheap generic stuff I have never heard of). This plus a new power cord and all seems fine. I could probably lick the back of my systems now and not feel a thing. (Did I just say that?)

    Again, thanks for the input, I feel a great deal more comfortable now.

    PS, the receptacles here have NO screw to use that ground wire on. The things snap on! Different strokes I guess....
    Last edited by malcore; 08-27-2002 at 05:03 PM.

  10. #10
    Join Date
    Nov 2000
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    The Mountain State
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    Boy, you should get out more often....
    I could probably lick the back of my systems now and not feel a thing.
    AV, Anti-Trojan List;Browser and Email client List;Popup Killer List;Portable Apps
    “When men yield up the privilege of thinking, the last shadow of liberty quits the horizon.” - Thomas Paine
    Remember: Amateurs built the ark; professionals built the Titantic."

  11. #11
    Join Date
    Feb 2002
    Location
    Nor'East USA
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    Where's MY "pi-jios" ?

    I just got off 'work' (the other 4 letter word...). Man! I'm parched! Is that stuff any good? Aw heck, as long as it's cold and wet it'll do fine.

    I'm glad you have your wiring and systems all in order now. You should feel safer with it that way. There's still several outlets in my flat that are only 2 wire but the electrical entrance has been changed and I will be running some additional circuits soon to accommodate all the pc's and other items I have here and to eliminate the 2 wire outlets.

    Is your modem surge protected too? It should be. And re-reading this thread, mjc's reply makes sense. Phone lines are 48 volts with limited current so a faulty telephone wiring could cause multiple systems to have a standing voltage that you would feel if touched. You should check that out too. Radio Shack and possibly other places have a very inexpensive test plug that you just insert into a phone outlet and it tells you if it is wired correctly.

    Right now I have the pc I am using and an air conditioner on an extension cord (I know, not a good thing to do) just so it can be on a 3 wire outlet. When the thermostat would call to turn the AC on, my pc would reboot! I quickly learned that I have to run one or the other.

    Now if you want to get 'kinky' and do this:


    to your pc, I won't tell anyone, promise. BTW, what do those 'dust bunnies' taste like anyway?!? Must need copious amounts of pi-jios just to wash them down I presume?

    Hmmm, maybe I'll dedicate a circuit for the refridgerator....
    There's no place like 127.0.0.1

  12. #12

    mjc's reply

    Of course, no reply from the SEGMG goes unnoticed! Modem and phone lines were the fist things we checked. All well.

    As to getting 'kinky' with my systems, it would take a great many pi-jios for this to occur. Although FTT's 'dust bunny' remark has put images of bunnies in my head: "Playboy dust bunnies." I have to admit as well, that slot load DVD player has been known to excite me.

    I think I'm sharing too much.

    FTT, if you ever get that "balloon" of yours up in the air and head this way, I promise you an unlimited supply of pi-jios. And yes, they are damn tasty, especially in 38 degree weather.

    mjc, I think we all need to get out more often.


  13. #13
    Join Date
    Jun 2001
    Location
    Statesboro, GA, USA
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    19
    I just disassembled a small surge protector, similar to what some of you may be using, and here is what I found: There are metal oxide varistors (MOV)'s connected between the hot and neutral legs, between neutral and ground, and between hot and ground. If you have a similar unit and it has an input power cord attached, and if you have it plugged into one of those 3 prong to 2 prong adapters because your outlet has no ground slot, you have a potential hazard. The ground wire in your computer's power cord is connected to the case of your computer. The ground wire in the power cord is in turn connected to an MOV in the surge suppressor which is connected to the hot leg, and of course the suppressor's ground is isolated because of the adapter. The MOV will conduct some current and you will be able to read line voltage between the case and a good ground or neutral. I just tried it on the bench by applying 120 volts to the hot terminal and I read 120 volts on the isolated ground terminal. If that particular MOV failed in the shorted mode, which is the most likely failure mode, then your computer case would be connected to the hot leg. You would then be possibly electrocuted if you were to touch the case and a good ground at the same time. Of course the solution is to plug the surge suppressor's cord into only a grounded outlet. Connecting the 3 to 2 wire adapter's green wire to the center screw of the outlet is no solution unless you verify that the box is grounded. On the side of safety, I would not assume that the screw and the box in the wall are grounded. I would not recommend using the 3 to 2 wire adapters on the output of the suppressor either, because doing so would isolate the grounds of your case, monitor, etc. and would possibly cause other problems. The only solution that would "meet code", I believe, is to rewire the outlet with appropriate conductor and install a 3 prong outlet. I realize that is not going to happen in a lot of cases. I hesitate to make any recommendation, but if it were mine I would attach the adapter's pigtail to some nearby known grounded object, or anything metal that you would be most likely to touch at the same time as the case. This would bond the case and the object so they would be at the same potential and you would at least not be hurt, but it ain't "legal" either. Note that I said bond and not ground. You could also open up the suppressor and remove any MOV or capacitor connected between hot and ground. They would have no function without a ground anyway. So yes, you probably did feel a tingle.

  14. #14
    Join Date
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    I had this problem and the outlet box wasn't grounded. I had to install a new outlet ran new wire all the way from the breaker box just to get a ground.
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