Electric shock in computer case : reason and solve

Discussion in 'Technical Repair' started by Willen, Sep 22, 2016.

  1. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi,
    I have discussed on the problem in past days too. And simple solution for the problem is to earth the case/chassis. However, which thing produces such electrically shocking leakage on the chassis? Here, most of the houses' wiring have no earth wire (just have two wire: 'neutral' and 'phase'). So when I stand in wet ground and touch the case, it gives painful shock, like I am touching mains.

    If the leakage is from a particular part of SMPS, like through a resistor or capacitor for example and if I grounded the case then current starts to flow through the part to the earth and the part dissipates power. So I guessed the part will be damaged due to over power dissipation, won't it?

    I am worrying because if I connected any devices to computer and touched any delicate parts of the device, I will get shock, as I explained before. Because USB cover are electrically connected to chassis too. So I think some part of the device may get explode from that current flow through my body to Earth.
     
    Last edited: Sep 22, 2016
  2. MrSoftware

    Member

    Oct 29, 2013
    497
    122
    Here in the USA, the neutral is connected to ground. I'm asking the crowd here; is there any technical reason why he should not connect his neutral to ground in the box where power enters his house?
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
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    Check the outlet you use to power this computer. I suspect the neutral and hot lines are swapped.

    That or the neutral is not grounded at all.
     
  4. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Nice question!
    - Once, during my teenage, I used to listen an AM radio powered by linear transformer based AC to DC adapter. Noise from all the arrangement was horribly audible in the AM radio. When I used to power the radio with battery, it was very clean. But really horrible with the adapter. Then I checked phase wire of the mains by neon based tester. Then I prepared an earth wire and connected to neutral wire in the mains. I do not know more, but the AM radio's noise decreased more and I was happy enough.

    - Once, I made a earth connection. I used the earth wire and I used neutral wire and watched a TV using the potential difference between the earth wire by me and neutral wire from mains! It was free electricity because I found that just 'phase' wire runs the electricity meter. :) Later they added an earth protection rod around their distribution transformer and the trick stopped working.
     
    Last edited: Sep 22, 2016
  5. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    I had much the same problems when living in countries with 220vac line feeds. My solution was a isolation transformer for electronics so I provide my own neutral and ground reference points for equipment shock safety.
     
  6. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi, we have just Phase and neutral, no ground. Do I need to create ground from earth and connect to the case?

    Hi, Being a beginning hobbyist, I may not be able to arrange all as you said for now. I will read about isolation transformer though.
     
  7. Morvan

    New Member

    Jun 24, 2014
    11
    2
    First of all, a responsible person can not install any devices towards risk for him, for the client and for the device itself, regarding equipment lifespan.
    If your indoor only provides two terminals, acquire one with three and evenly a ground connection. We are talking about economy and human lives. The cost is and never will be the matter.
    Here, Brazil, during too much time electrical plants were 2 ways. Even this time, I used to ground up every touchable parts.
    Now a days, homes use to have trhee terminals and number of casualities and economy losses has diminished enough.
    Persons are more conscious of correct use of electrical energy. Industry, here, is very commited to respect standard. We need, too. It is not spencer or cheap. Just necessary.
     
  8. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    A common problem with a two wire power feed in countries with an overloaded electrical infrastructure is that you have a loaded (weak) neutral from the many taps between the distribution transformer earth neutral bond and the load. Between the neutral wire and hot phase might be ~220vac (depending on the time of day) but the voltage between local earth ground and the neutral might the 50 or more volts at times. There's also a tendency to up the transformer supply voltage to compensate for overloaded supply lines voltage drops. In my rental houses I had a 5kVA 1:1 isolation transformer with a ferro-resonant voltage regulator between the input and equipment.
     
    Last edited: Sep 22, 2016
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I would not recommend doing such without local professional advice. "Local" as they would know your local conditions.

    My house was built before 3 prong outlets were required, though the box is grounded. Some of the later additions adding the ground prong were installed backward swapping hot and neutral. That's not an issue when just using the outlet for lights, I is a problem for other things.

    If you have a nearby earth ground such as a metal water sink with metal plumbing you can use that as a ground reference so a meter can show you if your neutral is grounded, or ifbthevwires are swapped.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,492
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    What is the derivation of the neutral and phase, I assume it is from a star connected transformer.
    If you provide an effective earth ground, ground stake etc, for the neutral at the service entrance, you should be able to set up your own safe grounded system.
    I assume the neutral conductor is correctly identified.
    Max.
     
  11. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    The neutral wire of my home has been connected to earth directly where the distribution transformer (11KV to 220V) placed, which is 200 meters far from my home.
     
    Last edited: Sep 22, 2016
  12. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    What you have is something is hooked up backward like has been posted the neutral is reversed. Or there to much drop that it is above ground level. The computer has ground tied to the neutral even thou you don't have a ground the case is hot because your neutral is not at zero voltage.
    Drive a metal stake in the ground and bring that inside and with dvm hook one lead to your stake and test the neutral and the hot and tell us what it reads.
     
  13. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Hi,
    Here are my 5 test conditions:
    Test1: voltage between Phase and neutral is 211V
    Test2: voltage between Phase and the earth is 219V
    Test3: voltage between neutral and the earth is just 0.9V
    Test4: voltage between computer case and the earth is 80V
    Test5: computer case grounded to earth with 1k series resistor and voltage between computer case and the earth is just 0.1V!

    I think the last test says that it's not so worrying problem. This is just a tiny current being leaked. So same as Test5, Can I use a 1k series resistor (for safety?) to ground the computer case and I won't get shock anymore.
    ? What you say?
     
  14. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    You have a bad ground at the power pole more then likely.
    The ground at the pole should bring the neutral to ground or 0 your showing 80 volts.
    Thats not good but if the neutral was bad it be way higher.
     
    Last edited: Sep 24, 2016
  15. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    I can see a high voltage green disc capacitor of '272' maybe, which connects computer case and SMPS electrically. So I guess the 80V leakage is through the capacitor. If 1k series resistors to earth can drop the 80V into less than 1V, then I can do the trick.
     
  16. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    You really need the power company to fix your problem hate to hear your dead cause you turned on the water and touched the computer at the same time. I fix about 10 to 20 grounding problems a week. Here they love grounding you have to install 2 rods and ground the breaker box to them.
    I've seen where the ground has been cut at the pole and water pipe changed to pvc you turn the water on and touch the stove it would knock you down. After doing some test the metal on the stove was at 100 volts. Had the power company fix there side and it stopped but I also installed new grounding on the house side too. Your setup is a little different you should be grounded where the power drops from the pole to you house.
     
    Last edited: Sep 25, 2016
  17. Willen

    Thread Starter Member

    Nov 13, 2015
    138
    12
    Not only in my house, I get electric shock in a office computer if I stand in wet ground, I get shock in the computer training hall too.
     
  18. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    Here is your problem
    [​IMG]
    I see why they don't care about grounding they don't want touch any while playing with this.
    I can't find how your metered but I'm looking you could ground it at your house but it needs to be a capacitor from both wires to ground. I'm thinking you have capacitive grounded system.
    Something like this.
    ungrounded system.png
     
    Last edited: Sep 25, 2016
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,492
    2,363
    From your results so far I would say you require a better ground from the PC case etc to a known good ground conductor, Desk/Tower PC's are generally already wired to the earth ground conductor, the DC side is also referenced to earth ground.
    Do your service entry supplies have a ground conductor re-referenced to the neutral conductor or do they rely on the earth path back to the transformer star point?
    You mention outlets being wired with no ground conductor, if this is the case, this is the result of the shock you get.
    Max.
     
  20. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    Max you can't ground a case that's 80 volts that's a big short to ground isolation transformer would work. If he use a resistor that could dump 80 volts but that's a band-aid.
     
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