Why would my case shock me?

Hi

I've noticed that I can feel tiny electrical shocks when I brush the edges of my case with my forearms. It even happens when I unplug the PSU from the wall socket and have the monitor connected to my gfx card (with the monitor switched on).

I've removed everything from my case and blown it out, after checking for loose screws. I've tried to isolate the PSU from the case and the 4 metal screws which attach my motherboard to the back-plate, using masking-tape. This didn't help.

(the screws also have those tiny red washers)

Is there a risk of blowing a component (and should I buy a wrist-strap), or am I being paranoid?

It may not be anything IN your computer, though it is a good thing to check around inside it to see if there's some loose wiring that's touching the case anywhere. Though I would try to make the psu-to-case contact better to make sure any stray shortages are getting to ground instead of to you!

To find if the stray voltage is being backfed from another place in the house, you need to make an isolated ground and test for voltage from your wall plug to it. You need a multimeter and a piece of wire (any gage). Strip one end of the wire about a foot, hang it out the window, and bury a couple of inches in moist dirt. Use the meter between the ground part of the pluggin and that new wire. You'll get a meter reading (check both AC and DC) if something else in the house is leaking voltage to ground. Since the ground of each and every outlet goes into the same bus bar in the circuit box, a leak into one socket can leak to them all.

I had a similar problem, a week before my water well pump went kaput. Since it was replaced, all is fine.
I now have a grounding rod sank outside for my computer system only, to keep any stray stuff in this ancient house from getting into my computer through the houses grounding bus.

its probably static electricity

Diggrr: thanks for the great tips. However, I'd like wire-lengths of 15m, since we live in a 4th storey apartment. It may be that the electricals in the block are dodgy, but I have no idea how I'll sort that out. I suspect that we've had some fluctuations which have caused two PSU's to die on me (although not in this PC).

Shawn: that's also a good possibility, since this region does have a fair chance of static and we're entering our dry, cold season. Our place has tiled floors though. Also, I would think that the static would drain off if I touched a grounded metal object? Instead, I feel a very mild, continuous current if I hold my arm against the case.


Thanks for the ideas.

Hmmm. 4th story huh? That makes it difficult.

Do you have a metal waterpipe nearby, or maybe even a steamheat pipe? Those would be good grounds as well that you could test with.
If the ground plug in the wall socket proves to be the source of the voltage, we have these plug converters that let you plug in a 3 prong plug into a 2 prong recepticle. There's a metal tab on them that would allow you to use an alternate ground source instead of the one at the wall...

Never thought to look and see what country you're in, electrical codes may well be far different from here. I'm not even sure if your electrical plugs are similar!
Sorry for that, but the testing should be similar.

I'm in South Africa. We have 230-240V/50Hz flowing from our outlets, which all have 3 rounded prongs (ground, live and neutral).

Are you saying that it's a safer idea to run a grounding wire from a waterpipe (or perhaps a waterheater/geyser)?

Also:

Though I would try to make the psu-to-case contact better to make sure any stray shortages are getting to ground instead of to you!

Click to expand...

In other words, is it recommendable to improve the contact between the case and PSU, instead of isolating the two as I tried to?


Thanks again, although I don't know how far I'll be able to test things.

I would make sure the hot and nuetral are not switched. I have seen that happen on one before and that was what was wrong. I corrected, at the plug in the wall, and all was well. no more zaps.

Many PSUs, including those in monitors, have low-value (about .005 uF), high voltage disk capacitors between the center prong and the other AC lines, and these can conduct enough current to be felt. I think that Antec/Channel Well PSUs don't have those capacitors.

I'm not very familiar with electrical wiring, but I think that U.S. 230V outlets for ovens and electric clothes dryers have 2 hot wires, 1 neutral, and in newer houses 1 ground. I think that fourth ground wire was added in case the neutral wire wasn't wired correctly, such as to the ground of a sub panel breaker box, as opposed to the main panel breaker box.

In my area the ground and neutral can be tied together. That can be bad of the wires are reversed at the other end, at the outlet. Most of our plugs are polarized and the case will be tied to the hot wire if reversed. Puter will still run but don't touch it.

Few home computers use 220 to 240 volts in the US. They reserve that for BIG stuff like dryers, stoves, heaters and A/Cs. More efficient they say. Maybe we should do that here. Save power.

Later