ground

[TheNiceGuy]

Hi all!
My PC (in sig) has a slight charge to the case. When I touch it, I get a low-level shock.
I'm guessing this is because I have no ground. The PSU has a ground, but here in Japan the outlets don't.
So can I just wrap a wire around the ground prong, and run it out the window into the actual ground? Or what?
Thanks!

 

[tcsenter]

The case could be the lower potential. i.e. the case may not be building a charge, you are.

These can be tricky things to figure out. I had a case that was giving me a little feedback several years ago, but never did figure out what was going on. I changed the PSU, the power cord, insulated all the mounting points, checked the outlet wiring, but it was still giving me a little zinger.

I discovered it while down on the floor trying to get at something, and I happened to touch the side of my face to the chassis. Zing! If you touched it with a part of your body that had thicker skin, such as your hands or fingers, you couldn't feel it. And it wasn't a quick 'zap' like static discharge, either. It was continuous. As long as you touched it, you felt it.

I even talked with an MSEE about it and he said it could be some faulty appliance driving the circuit high, like a TV or refridgerator. Is the floor concrete slab with a covering like linoleum tile?

 

[spittledip]

I had that same problem with an old dell. You would get a continuous shock by touching part of the interior case if it was plugged in. Never bothered to figure out what was causing it.

 

[mpilchfamily]

Well since the outlet where you are doesn't have a ground the adapter you are using should have some means of compensating for it. Likely the charge you are getting is from you and not the system. This happens all the time for me in the winter when the air is dry and static electricity builds up easily. The fact that you are getting the shock shows the system is ground in one for or fashion.

 

[jaqie]

Proper grounding steaks are actually copper clad and 8 feet deep in the earth. Unless you purchase and install one of those, your only other real recourse is to check to see if the water feed coming into your house is made of metal or another material. If it is metal, you can use it as a grounding plane, if not, or you are not sure, use the steak. Check out whatever construction supply stores are around in your area for grounding rods.

 

[Modelworks]

If you were to look at the ground in a USA breaker box , often you will find that the ground and neutral occupy the same bus bar.
Before the separate ground wire in the USA it was common to see appliances that used the neutral for ground.
Its the reason why there is still one side with a larger slit than the other in the socket, so that older appliances do not connect the hot side to the chassis when plugged in.

The reason you are getting shocked is because something in that case is tying itself to the home wiring.
If the case were truly ungrounded with no connection to the home, then it would be just like touching a knife or fork on a table, just a piece of metal.
Often what happens is the neutral in the pc power supply is connected to the ground of the pc.
Its usually a high resistance connection but its enough to shock.

What could be happening in your case , is that the hot side is swapped , either on the outlet or adapter.
The pc will still work, but the hot side is connected to the case instead of the neutral.
That will cause you to get shocked if you touch the case.

Get a multimeter and set it to AC.
Then place one probe on the neutral side of the outlet and the other on the pc case.
There should not be any volts showing, mV are normal.
If there is , there is leakage somewhere that should be corrected.

Also try disconnecting devices from the pc.
You could be getting leakage onto the pc ground from monitors, speakers, etc.

 

[jaqie]

Actually, modelworks, I find much more often then not that in the case of a floating ground situation like this, it is actually the D sub of the monitor feeding some AC back into the case through the D sub shield thenn anything else, and properly grounding the outlet solves the issue, as the monitor has proper ground (which is what seems to be hooked to the D sub through internal monitor wiring and thus causing the live case).

 

[TheNiceGuy]

Thank you all so much for the support!
My situation sounds a lot like tcsenter's. I didn't notice until I touched the case when it was humid, and then I got a continuous, low-level shock. It also happens if my hand is a bit wet (ie sweat). It's enough to be uncomfortable.
Occasionaly, I get a "low power warning, lowering graphics card performance to avoid damage" type warning at startup. Related?
Also, this is an older house, and I wouldn't be surprised if there are power issues. For example, the breakers go if we run too many appliances at once, my shaver's speed oscilates sometimes, etc. That sort of thing.
Any ideas?

 

[Modelworks]

Does the house use aluminum wiring ?
Its well known for becoming loose over time.


Another thing with older houses is that the service is undersized.
The houses were wired for the electricity usage at the time, which was mostly lights , stove, refrigerator.
Things that are added now like Air conditioning, microwaves, computers, big screen tv, etc overload the service.

200 Amp service is the average in USA.
I have seen older homes with 100 Amp or even 60 Amp service and tons of things running off it that shouldn't be.

 

[Elstupido]

Question, is the box that houses the receptacle grounded? If so just get one of those 3 to 2 prong adapters and put the ground strap from the adapter under the hopefully grounded metal plate screw.

You need to use caution using a ground rod without grounding that to main system ground as a difference in potential can develop during a lightning strike. The newer National Electrical Codes require all ground rods to be bonded together.

On another note, I have no idea how things are wired in Japan. I had my hands full with wiring here in the states alone when I was an electrical contractor. You really need a multimeter to test your actual voltages at your outlets under load to determine if you are encountering an under voltage problem. What voltage and frequency is Japan running these days?

 

[TheNiceGuy]

Where I am they use 100V/60Hz. But I think most homes here are underpowered and poorly wired, like ours.

 

[RallyMaster]

And after two years of electrical engineering, I still don't know what ground really is.

 

[us3rnotfound]

Originally posted by: TheNiceGuy
Where I am they use 100V/60Hz. But I think most homes here are underpowered and poorly wired, like ours.

Do they make PSUs that run under 115V?

 

[RallyMaster]

PSUs are now commonly rated to run at 85V to 230V AC. A lot of the recent APFC ones don't have the voltage selection in the back of the unit (I think pretty much none of them do).

 

[us3rnotfound]

APFC oh god

 

[Mark R]

Originally posted by: us3rnotfound

Do they make PSUs that run under 115V?

Most PSUs should run OK down to about 90 V.

Active PFC PSUs are 'universal' voltage - they'll run from about 85 - 270 V.

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There are a number of subtleties with grounding. If you're not careful, you could potentially make the situation more dangerous.

As it is, equipment with exposed metalwork on it, powered from an ungrounded outlet is potentially lethal. If, the power surge absorber in the PSU fails (e.g. due to a large power surge), or if a wire comes loose in the PSU, it could connect the PC's case direct to the hot line. You risk electrocution if you then touch the PC, or anything connected to it.

The other necessity to make the situation safe is 'equipotential bonding'. You need to make sure that, if power were somehow to get connected to ground, that one 'grounded' bit of metal, doesn't drift to a different voltage than another bit of 'grounded' metal. E.g. PC is 'jury rigged' to ground onto a water pipe which is grounded because it's metal and goes underground. If the PC malfunctions, then the high voltage is connected to the water pipe (but other water pipes, or heating pipes) might not touch the water pipe, but still be grounded via a different point. This means that different water pipes may have different voltages. E.g. the hot and cold water might be at different voltages - touch both taps and the same time and zzzzzap.

If you're going to ground metal pipes, fittings, etc. They all need to be strongly connected together by heavy cables, so that the voltage on all metal in a region is held to the same level.

The other problem is that if you ground to a spike in the earth, then it doesn't offer adequate protection on its own. Earthing rods provide a high impedence ground connection. This is not enough to shut off the power, in the event of a ground fault. If you use a ground spike, you must have RCCBs on all circuits that use it. This will ensure the power is cut off in the event of a fault.