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Power Supply Leaking Electricity to Computer Case

Posted on 2004-08-29
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Last Modified: 2012-05-05
It seems the power supply is leaking electricity to the computer case. when the computer is plugged in and turned on, if i touch any metal part of the computer (including case, hdd, etc) i can feel a current flowing through me. Is this due to bad power supply?? should i buy a new power supply?? thanks :)
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Question by:jhson114
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by:DVation191
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uhhh...thats not a good sign :)

you definitely have a short ...whether its a bad PSU or an exposed wire is hard to say without seeing it. I'd hightly recommend a new PSU in either case.
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by:jhson114
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how much power would be enough for p3 800mhz? 300watt??
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by:jarich
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I would recommend trying a new power supply first also, but the voltage you are feeling can be coming from any short to ground, such as the motherboard mounts or a drive unit. Check out the wiring for shorts to ground, disconnect power to drives one at a time and remove the motherboard from case and place on an antistatic surface for testing. Buy a good power supply such as Antec or Enermax, 300 watts should be fine unless you have extra drives.
Jerry
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by:DVation191
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Just match the same or better wattage that you have now. Make sure you get a quality power supply though... like something from PC Power & Cooling,  Enermax or Antec Truepower
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rid earned 50 total points
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The situation can only occur if you are using a non-grounded outlet. Some leakage is always present and you can feel "electricity" if you are the path between the computer and "ground" - the current is very small however. If it were a real short you'd be made aware of the fact in a more spectacular manner (electric shock). Of course, if you're in a high-resistance environment (wooden floors, rubber-soled shoes etc) you may have a potentially very dangerous situation at your hands as the current is limited by those factors. Touching the computer and at the same time something like a water pipe may be hazardous. There is dedicated equipment to measure insulation values in the power supply, but you'll probably have to call an electrician to perform the testing.

Verify that a grounded outlet is used. This ascertains that the computer case is always at ground potential.
 If a grounded outlet is indeed used, check plugs and cables thoroughly.
/RID
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by:onsitez
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It IS very dangerous situation, because you touching the case are now the ground. Thats why there are three wires. One wire is hot, the second wire is the return for the hot and the third wire is ground and is attached to the case or chasis. Lets say in the old days when there were just two wires, the hot and return for the hot, that the return wire came loose inside and touched the metal case of say an electrical appliance. That wire touching the case would energise the case with 120v ac AND would not pop the fuse or trip the circuit breaker. Now some one comes along with wet hands and no shoes , theyy touch the appliance , 120v goes through there arm and down their leg to ground...U R THE GROUND.  If there is a third wire (ground) attached to the case, the instent the return wire touches the case the current flows out the third wire ground causing a short opening the fue or tripping your circuit breaker in the wall panel ..or in the case of a dumb friend of mine that put a nickel in place of a fuse in his wall fuse box and when he got a short there was not a fuse and his house almost burned down. ....I digress, Anyway, U have an open ground or as someone mentioned before U might not have a grounded outlet...in anycase you are in a D A N G E R O U S situation.
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by:wyliecoyoteuk
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'scuse me, but.....if the case IS adequately earthed then....
You can get a shock if YOU are charged up with static, and you touch the case.
I would first check the earthing of the case, and then try isolating the static causes.( nylon clothes, plastic shoesoles on nylon carpets, etc).

computers are often the best earthed equipment in an office, and then they are a static magnet.

IF IT IS NOT STATIC then it is potentially(sic) a VERY dangerous problem.
(also static sparks can kill your processor)
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by:derenm
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Ditto -> BAD.

The chassis does act as a common ground, however, there should never be a noticable current that you can -feel-.  This is a bad thing if you do.

Chances are, it seems like there is a short that is somewhere in your PSU or in one of your components.  There is -usually- not enough current going through any part on the board that is strong enough to kill, however, a leak from the PSU can be very dangerous.

Nail down the problem and fix it ASAP.  This will have to be done with a carful pyhsical inspection, as well as a change in your PSU.  Period.
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by:pjcrooks2000
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Hmmm what a very weird problem,

I am suprised you have not had a fire if what you say about having  a short is true...

Try this first, make sure none of your power supply leads are exposed and touching the inside of the case, what I mean by that is that sockets that plaug into your devices....

If you were conducting AC power then yes it would be sending AC power to ground through your kettle lead, so I guess it will not be that because you would trip out your electricity if that was the case or in fact you would have blown a fuse at least.


It will not be static because again your case is connected to earth, earth connections crain away static.  I suspect and as a former electrician that the voltages that are being leaked to the case are being absorbed by the ground connection and this means that the voltages will not be very large... That would point to the 5v connection (yellow wire) from the power leads jumping to earth "the case"  Or one of your peripherals, motherboard or another device is somehow touching on the case... Luckily for you the point that it is touching the case if it is at all is on its return route to earth but may still have a residual voltage.  So in this case it would mean screws or plastic lugs missing from the motherboard (see next paragraph)

More commonly I would think the problem could be a faulty motherboard, so take everything out of your machine and make sure it is not coming into contact with the case.  Make sure you have all of your screws that raise the motherboard a notch away from the case inners are fitted.  

I don't actually think it is dangerous in a sense that it will catch fire otherwise it would have done that already.  Are you having any other problems at all with any of your devices?  

Again I stress check inside your machine that nothing is touching the outter case, include motherboard, Wires, Other cards etc etc.  Also as an afterthought make sure that you have not used screws in your drives that are too big as these may be shorting inside the device and carrying a current to the case.  But you will know that if you had a problem with a device.

Good luck me ole chap

pjcrooks2000


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by:_
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I have to go with rid on this one. Most of the time this means a faulty/bad ground in the wall socket. I used to get 'tingled' all the time, and this was the problem.
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by:wparrott
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Just adding my two cents here...

Have you verified that the outlet is grounded? I live in an older house and I had a similar situation. The outlets in the house were all the 3-prong type but in fact the ground lug was not hooked up to anything (the wiring was the 2-wire type). Any hardware store or a Wal-mart will sell a device that you can safely use to test your home wiring. It's a device that you plug into the outlet and it has LED's that tell you if the wiring is correct. Only costs a couple of bucks and is well worth the piece of mind.


Hope this helps...
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by:pjcrooks2000
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good point above I forgot to mention it but did think about it as I quote my 1 and three quater cents :)
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by:jhson114
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i checked out the outlet and it is grounded, but it seems the multiplug module (its pretty old) i use does not have the third plug for ground. guessing this caused the whole problem? i connected the computer directly to the outlet and problem solved! i cant feel the current any more. gonna go buy a new one multiplug.
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by:pjcrooks2000
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Ahhh yes that could be it,  The plug is then using your case as an earth pint.

Do replace your power supply with imediate effect.

well done!  :)
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by:rid
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If the PSU is indeed faulty, it'll blow a fuse once proper grounding is achieved. Otherwise I don't think the PSU needs replacing. The "tingling" sensation described by coral47 is the result of small leakage currents that you can find in a new PSU as well.

Of course, if you feel uncomfortable with this PSU, get a new one.
/RID
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by:pjcrooks2000
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Not so Rid if the ground wire is returning through the case, trust me I am an electrician  :)

The ground wire that is missing will cause the ground electrical current to travel to earth, probably through the device it is connected to.  The ground on the PSU should really go back through the power supply so that it can dissipate any last current before it is made totally safe.

I would say whatever device the lead with no black (negative wire) is connected to will be hitting earth through that device and not through the PSU where it should be, what you can feel on the case is the risidual current flow of a DC negative feed.  It is actually safe but I would prefer to have the Negative feed travel back to the PSU where the Positive feed for the circuit orinated from.

Good luck again!  

PS power supplies are not expensive ....
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by:rid
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If the PSU leaks from the phase (live) lead to the case, the mains fuse will blow if the case is grounded. Period. If the leak current is small (a small leakage current is always present) nothing happens except you will NOT experience the "tingling" when touching the case, as it will be at ground potential IF the computer is hooked up to a properly grounded outlet. Whatever happens at the secondary (DC) side of the PSU will not be felt by any human touching the case as these circuits are galvanically separate from mains power. The "tingling" comes from leakage current going to ground through the person touching the case, INSTEAD of going to ground through the proper path, which should be the wall outlet ground connection.

Never use an outlet without a proper ground for an appliance with a metal case!
/RID
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by:wyliecoyoteuk
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Just a fe3w comments about static and potential.

Earthed connections do drain static, but if YOU are charged up (walking on nylon carpet with plastic soled shoes, etc) then a spark will jump from YOU to any properly earthed object like a computer case, or a display case in a shop, for example.

If the case is not earthed or isolated  correctly, it will be at "floating" potential, which will lead to the tingling sensation.
This does not mean that it is live, merely at a different potential to earth, due to transduction (the case acts as part of the AC transformer loop)
If that is the case, then you function as the path to earth, hence the tingle.

I work on photocopiers, which are electrostatic devices, and rely on a good earth connection to work correctly.
Unfortunately, this means that any metal parts are very well earthed, and we often have problems with static shocks, although the equipment is not faulty in any manner.

All equipment should be earthed, unless it is "double insulated".
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by:pjcrooks2000
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Yes everything connected to the case should/would be earthed.  

I think hes getting a risidual flow of DC current from somewhere, not voltage "Current"  Not the same thing.  But both can travel though you.  

The case itself is acting as a circuit that is dissipating current.  Due to a fault with an earth current flow.  If it was a positive current flow then you can say bye bye to all your bits and reach for the fire extinguisher.  Thats based on the fact that it has not tripped your ac supply out first :)
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by:khanint
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this problem only occurs when there no proper earthing in your powerpoint so please consult your electric technician
and ask him to check the earth system in your power point.
iam sure this will solve your problem.
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by:pjcrooks2000
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Anyway enough hes solved it no earth point to take away his negative flow in his plug :)
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by:jhson114
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wow so many comments. anyways, the problem is already solved. thanks everyone :)
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