Stray Volatage, and how to mitigate it.

[Geoffric]

I noticed in working on my computers in the basement the last few days that I would get very low "tingles" of voltage, that were not strong enough to be called a shock. I really noticed it if my bare skin was touching a "sharp" point on the case, or the trailing edge of the side panel. Because of the small surface area on these "sharps" a better electrical conductivity was made and so I felt it more strongly. I had a friend with a voltmeter check it out and there is a slight current running from the cases of all three computers to ground. I am wondering how to mitigate it, and what causes it. Perhaps I have worn insulation somewhere shorting to ground and that is where it is coming from. Perhaps the electrical outlets have reversed polarity?

I thought if I attached some 18 gage woven copper speaker wire to a casing screw on my rig, and attached the other end to water pipes in the basement, would that fix the problem? The following is cut and paste from WIKI.

Thanks for any help you can give me

Stray voltageFrom Wikipedia, Stray voltage describes the occurrence of voltage between two objects that should not have any voltage difference between them. Small voltages are often measured between two grounded objects in distant locations, due to normal current flow in the power system. Large voltages can appear on the enclosures of electrical equipment due to a fault in the electrical power system, such as a failure of insulation.

Small stray voltages may never be noticed and may only be detected with a voltmeter. Larger voltages may have a range of effects, from barely perceptible to dangerous electric shocks. Normally, metal electrical equipment cases are bonded to ground to prevent a shock hazard if energized conductors accidentally contact the case. Where this bonding is not provided or has failed, a severe hazard of electric shock or electrocution is presented when circuit conductors contact the case.In any place where equipment is in direct contact with a person or animal (such as pools, surgery, electric milking machines, and many others), particular attention must be paid to elimination of stray voltages. Dry intact skin has a higher resistance than wet skin or a wound, so voltages that would otherwise be unnoticed would be significant for a wet or surgical case. (or in my case a stronger contact by compressing my skin over a sharp)

2.6 Neutral return currents through the ground

[Stray voltage defined as " A voltage resulting from the normal delivery and/or use of electricity (usually smaller than 10 volts) that may be present between two conductive surfaces that can be simultaneously contacted by members of the general public and/or their animals. Stray voltage is caused by primary and/or secondary return current, and power system induced currents, as these currents flow through the impedance of the intended return pathway, its parallel conductive pathways, and conductive loops in close proximity to the power system. Stray voltage is not related to power system faults, and is generally not considered hazardous. "on the phases is not exactly equal, there is some current in the neutral conductor. Because both the primary and secondary of the distribution transformer are grounded, and the primary ground is grounded at more than one point, the earth forms a parallel return path for the neutral current, allowing part of the neutral current to continuously flow through the earth. This arrangement is partially responsible for stray voltage. [10]

[bruce]

Do you have any Ground-Fault-Eliminator outlets nearby that could be used to isolate a specific computer with a problem? Can you borrow something like this?

Is everything connected with properly grounded power cables?

Have you checked that the outlet(s) you're using is properly grounded? ( Borrow one of these?)

[Qinsp]

In a perfect world, your computer case should be grounded. If something does go haywire, you won't get shocked by touching it. It also reduces radio interference.

Normally this should be handled inside the powersupply itself, and the PS case is bolted to the computer case with a bare metal contact. Painted powersupply cases are iffy. One of my powersupplies has a dedicated grounding strap for the case. Mushkin? brand.

But Bruce has the best idea, you need a ground fault detector or interrupter to find the culprit.

[Phantom2487]

Check the grounding at your power source (wall) 1st, try a different power cord 2nd, and 3rd verify the PSU has a good ground to your case (most points were aforementioned) but that would be the most efficient rout to take considering all the primary faults.

EDIT: I re-read that last part of your post and noticed something... test between the ground in on your outlets to a water pipe, and see if you have some form of a charge on your ground ?! I guess your ground in the wall outlets is different than your true ground in your house -- a copper water pipe..

[7im]

Also check if the main electrical service is not grounded well (you may need pro help with that). Sometimes the grounding wire comes loose from the pipes or grounding rod. If you live in a dry climate, they may need to drive a 2nd grounding rod for proper operation. I've also been told to pour a bucket of water on the ground surrounding the grounding rod between too infrequent rain storms.

[Geoffric]

I puiled the outlet covers and could not believe it Well, I know this is bad, but none of the outlets in the basements are grounded. When my dad wired this basement 35 years ago, he didn't ground. He also never used wire nuts, just twisted with a plier and used black tape. Worse the outlets I use actually run up to one of those 6" round ceramic light bulb outlets and insteasd of wiring up to the outlet itself go through one of those screw in the light bulb outlet.
The only way I can get to the outlets is to take the paneling off. I have been bugging my mom about it, but it's like "It was fine for 35 years, why change it now!

I will take the 2 outlets I use and go from the grounding screw on the outlet and run a wire to the water pipe and solder it on.

[chrisretusn]

I noticed in working on my computers in the basement the last few days that I would get very low "tingles" of voltage, that were not strong enough to be called a shock. I really noticed it if my bare skin was touching a "sharp" point on the case, or the trailing edge of the side panel. Because of the small surface area on these "sharps" a better electrical conductivity was made and so I felt it more strongly. I had a friend with a voltmeter check it out and there is a slight current running from the cases of all three computers to ground. I am wondering how to mitigate it, and what causes it.

This is normal were I live. Power to my house is poorly grounded two phase power. Running a grounding wire between case and ground will eliminate the minor tingles. I just live with it.

[gwildperson]

I live in an old house. The part that was build ~1930 has no ground and all the outlets are 2-wire. No wire-nuts as far as I've seen, but all of the wires are around the screws on the receptacles, instead, which is fine as long as you don't have to work on in the box. I'm not sure what they did in the boxes for light switches. The boxes are metal and I think they're probably grounded.

There was a major addition around 1955 and that part of the house is properly grounded. They must have changed the "code" about then. At least the whole house has copper wire instead of aluminum.

If you've got 2-wire outlets, you know you don't have a ground, but if you have 3-wire outlets that are not grounded, you need to get them fixed. Look at the second thing that bruce recommended. I do recommend that you get one.

[Slash_2CPU]

I wouldn't solder the ground line to the pipe. If that's a 35-year-old pipe, you are asking for trouble by heating it. Use a stainless worm-drive clamp.

[justjohn]

Geoffric: probably the best advice is "get professional help".

I'm only an amateur (wired two houses as an owner-builder), my point of view is that I plug in a circuit tester, if it says "correct", fine. If not correct, it needs to be corrected.
http://www.homedepot.com/h_d1/N-5yc1v/R ... ogId=10053

Sounds like it was wired in the '70s, did the wire include a ground wire? If so, I don't understand why you can't take the covers off and re-do each outlet correctly. If they are only 2 prong outlets, it costs about 75 cents to get a 3 prong, grounding outlet. Obviously this is a much bigger project if there isn't a ground wire, or if you can't get into the outlet boxes without taking down paneling. (I don't think the lack of wire nuts is a big issue, I thought I read that a good twist was as good. But really, the outlets I'm familiar with connect one side to incoming power, one side to outgoing power, so you don't use wire nuts on the live wires, only on the ground wire. Where I live, in the '80s, code was to use wire nuts to create a pigtail to hook up the ground wire.)

I would be leery of doing the modification (running a ground wire directly to a copper pipe) without fully investigating what is going on. You might make the situation worse by creating new loops. At any rate, I don't think the code allows for that type of jury-rigged connection. Why not just fix it the way it is supposed to be? Especially in a possibly damp basement, I would worry about shocks. If you don't feel comfortable about working inside the main electrical panel (there are hot spots in there, even if the main breaker is off), get help.