Static and ground question

Ok, I randomly built up a static charge big enough to make plastic wrappers stick to me like I was a magnet. I was worried about touching some stuff on my computer with that charge, so I held the back of the case near the power supply to try to discharge it. I was under the impression that the whole case was grounded through the power supply, and touching it cleared a static charge.

No luck, things were still sticking to me after I held it. So I went and held some plumbing that was grounded, came back, and the charge was gone. Does this mean my case isn’t properly grounded? Is something wrong? Or do I have a misunderstanding?

Could be an improperly grounded outlet. But also remember that it takes time for a charge to dissipate from an insulator (sometimes a lot of time), like the synthetic material your clothes may contain. I assume you menat the stuff was sticking to your clothing and not to your bare skin?

No, bare skin. My hand, specifically. Is that strange?

I could hold my palm perfectly flat and hang a plastic wrapper under it and there’d be nothing sticking or anything, just clung to me like a magnet…

Your case was grounded with respect to the power in. That ground is not good enough for static charges.

I’d say your computer case is either not properly grounded or the outlet it is plugged into isn’t. If you have a VOM, you can check. Put the meter on a setting to read line voltage AC, put one probe against a bare metal part of the case and plug the other into the hot lead of the outlet. BE CAREFUL! You should read full line voltage if a ground is present.

Did you hold a part of the case that was bare metal or painted?

Was the power plug in the GPO? If it was that should have grounded it, otherwise the case would be insulated from ground, though at the same potential as you.

Hmm. Well, parts of my case are missing, and sometimes I’ll bump the hard drives with my hand accidentally or something. I worry I might’ve discharged a bit of static onto them, so I grab the back of the case and the drove for a moment to discharge any static that might’ve built up. I was under the impression that that worked.

So, it doesn’t? Holding the back doesn’t impart a ground to me? Does the IDE cable of the hard drive provide enough gounding to clear it of any static?

Bare metal - what’s a GPO? Wall socket? Yes, it was plugged in.

The power ground, if installed correctly, should be more than adequate to discharge static charges. Where are you getting your info, AcidKid?

If you are at the same potential as the case, that is all that matters - you just need to be grounded wrt it to prevent damage.

I should note that I’m not actually touching the power supply, but the back of the case near the power supply. I assume the grounding transfer to the case.

you must be very attractive.

GPO - power plug.

Maybe parts of the case are not grounded. Worthwhile getting out the continuity tester.

I was just going to say - are well all sure that every point on the external surface of the case can complete a circuit to ground?

The main reason for having a ground on a metal case is to protect you in case something shorts to the metal. If it’s not grounded, the worst case is that the 120 V hot shorts to the case which could easily be lethal. It’s true you won’t damage anything with respect to static, but the main safety requirement of the case being grounded is missing.

I suspect that either the ground in the outlet is either fauly or not connected, or the ground connection inside the computer was never connected to the case.

Well, does anyone know if it’s standard for computer power supplies to ground the case?

Typically a power supply will have a green wire with a lug on the end which you are supposed to attach to the case somewhere. Usually the metal case of the power supply is not automatically grounded.

From the OP.

This indicates that he may have no ground or a poor ground in the house wiring. In any case, I never trust the building wiring when grounding a workshop static mat even if it tests OK with my handy dandy outlet tester. I even look at the plumbing to make sure there is no PVC pipe. A copper rod driven into the ground is sometimes necessary.

Ah, I misread you, AcidKid. I took you to mean that a power ground in general is not good to dissipate static. My apologies.

Are you certain that YOU were charged? After all, if the wrapper was charged instead, it would stick to your hand.

I can rub a plastic wrapper on my sweater, and afterwards the wrapper will cling to my hand, the ceiling, etc. Works with balloons too!