shock from power supply

[JPerk]

I have an old pc that I have been using for about 5 years. Not sure if specs are needed but its an amd x2 5600+ to show how old it is. About 2 years ago the power supply stopped working so put in a new one. That's the last time its even been opened.

Today, I went to plug in a usb mouse while the computer was running. When I touched the top/back of the case, I felt a very minor shock. Out of curiosity (or stupidity), I reached a little further down the back of the case so that my hand was in the middle of the power supply. This gave me a bigger shock.

I plugged the mouse in and everything works fine. It's still running but I haven't touched it again to see if it would shock me again.

Is this likely a problem with the computer or the wiring in my house? I did just move there a month ago and don't believe I have ever touched the computer while it was on since the move.

Should I try touching it again or is that risking the motherboard, processor and ram?

 

[C1]

Connect a voltmeter (120 volt AC scale) between the computer case and the ground terminal of the wall socket (ie, the left slot of the wall socket that is the largest slot). If you get a deflection, then this should be remedied. (I would inspect the PSU and replace it if necessary.)

 

[denis280]

Should I try touching it again or is that risking the motherboard, processor and ram?

Very bad. just do like C1 told you.

 

[lakedude]

Connect a voltmeter (120 volt AC scale) between the computer case and the ground terminal of the wall socket (ie, the left slot of the wall socket that is the largest slot). If you get a deflection, then this should be remedied. (I would inspect the PSU and replace it if necessary.)

This is completely wrong.

On a 3 wire outlet the ground should be the round pin.

OP when you say "shock" are you talking about one little zap, like static, or an ongoing shock as long as you touch the PS?

I suspect improper house wiring because even if the power supply was bad the ground wire should prevent a shock, unless the shock was just static.

 

[lakedude]

I would invest in one of these (or something similar):

http://www.amazon.com/Gardner-Bender.../dp/B00170KUPC

 

[lakedude]

So the way an outlet should be wired is as follows:

The "ground" is the round pin. It is wired literally to the ground. A big copper colored rod gets pounded into the ground and all the ground wires in you house should be connected to this rod. Under normal operation no current should ever flow in the ground wire. It is for safety only, not for carrying current!

The smaller of the 2 flat blades is call the "hot" side, and the larger of the 2 flat blades is the "neutral" (NOT THE GROUND).

There is a big difference between neutral and ground. The neutral is designed to carry current and the ground is not.

 

[lakedude]

If the shock was just static it would be completely normal for you to get a spark when you touch something that is properly grounded (like a computer power supply) and if this is the case there is nothing to worry about. In this case the voltage is actually built up on you and the spark happens when you ground yourself, removing the built up charge.

OTOH the house not being wired correctly is a huge safety concern. That you just moved recently also supports the bad wiring theory...

It is very unlikely that a power supply would ever shock anyone if it was properly wired. The only way this could happen is if the ground was open (broken) and at the same time a wire with current shorted to the case. Both these things happening at the same time is very unlikely.

 

[Steltek]

Getting shocked twice simply by moving your hand isn't static - a static charge would have discharged with the first touch and been pretty much gone with the second. You definitely have a problem which needs to be resolved ASAP.

Do you use a UPS on the computer? If so, it would normally sound an alarm or have a light which flashes to indicate a wiring or grounding problem exists.

If not, the outlet checker lakedude linked above is a good start. You should be able to get something similar at any Walmart, Home Depot, or Lowes. It will at least tell you if polarity is correct and that the outlet itself is properly grounded (an entirely plausible issue in an older home, or one in an area where electrical codes are enforced in a lax manner). If something is wrong with the outlet, you'd be advised to check outlets in different rooms to see if any problems exist on different circuits in the house. The inside of your main breaker box door should be labeled to show which rooms are wired on each circuit.

 

[lakedude]

If something is wrong with the outlet, you'd be advised to check outlets in different rooms to see if any problems exist on different circuits in the house.

^This

Getting shocked twice simply by moving your hand isn't static - a static charge would have discharged with the first touch and been pretty much gone with the second. You definitely have a problem which needs to be resolved ASAP.

Good point. If you notice I said that I suspected wiring early on. Also it is not heating season so static shocks would be less common...

The evidence is really pointing to bad wiring at this point.

 

[Phallic Moron]

I have nearly the same exact problem. Most definitely not static shock as I get bit just by touching the end of a USB cable. All outlets in the house have open ground. 3 prong outlets included. I did not notice any shocking with a 280 watt PSU. I installed a new video card and a used 550 watt PSU, and that's when I noticed the problem.

I'm going to try some other PSU's and see if that doesn't help. It doesn't make sense. I don't get shocked when I'm touching the air conditioner, the coffee maker, etc. etc.

The only thing I can think is that the 280 watt PSU just didn't draw enough for me to notice, and now that I'm drawing 550 watts it's more more noticible. I have to move the PC with socks on my hands because it hurts!! Sorry to threadjack, but I'm really trying to solve this problem.

The high wattage appliances have ground fault interruptors installed at the outlet or on the cord itself. It's my understanding that having one of these will protect ME, but not my PC.

 

[lakedude]

So Phallic you already know your house has open grounds? Even with open grounds a PS should not really be shocking anyone. The ground wire is there just in case and shouldn't be needed unless there is another issue.

There are 2 common ways to offer protection from electric shock: Grounding and double insulating.

With double insulation if there is a problem with an inner conductor a second layer of insulation protects the user. So if a hot wire gets loose inside a drill for example the user is protected by the plastic shell of the drill and the hot wire spins around harmlessly inside. This is a good system and works great with 2 prong outlets. Only problem is you might not ever know your drill has a loose wire.

Grounding is the other method. Ground wires are connected to the ground and the operator is standing on the ground so they are at more or less the same voltage potential. Current will only flow when there is a difference of potential (well maybe in some exotic super conductor) so if the drill is at ground and you are at ground no current will flow and no shock will occur because you are both at ZERO Volts. Grounded drills have a metal case and that case is electrically connected literally to the ground. If a hot wire gets loose inside a grounded drill the user is protected by the metal case AND the ground wire provides a low impedance return path causing a current surge which should trip a breaker. So in a way the ground method is better because the user is protected and there is evidence that the drill has loose wire.

The problem with the ground method is that it requires an extra wire and it requires that the extra wire be in good working order. If a system is supposed to be grounded and it isn't that is a safety hazard. For example say a metal drill is supposed to be grounded but someone snapped the round pin off to run it in a 2 wire outlet. In such case if a hot wire comes loose and hits the case the case will then be energized to whatever voltage the hot wire is and if you are holding such a drill you will get shocked because the voltage from the hot will use your body as a return path to ground. If you are completely dry and your skin has a high resistance you might just feel a tingle but if your skin resistance has been lowered from sweating you might just up and die right then and there.

 

[VirtualLarry]

my friend, when he first moved into his new apt, was using a power strip for his computer equipment that had a 3-to-2-prong adapter plugged into the end of it. When he hooked up his computer, touching the back of it would give you a slight shock. Unplugging the 3-2 adapter fixed the problem, by allowing the ground pin to make contact.

 

[C1]

http://www.thecircuitdetective.com/test.htm