Why is my jumpdrive shocking me?

August 6, 2008 10:32 PM

While plugged into a USB port on my PC, my recently purchaced jumpdrive (Sony Microvault 4GB) mildly shocks me as I try and handle it. It is pulsing with a current. Obviously I'm going to return it, but what I would like to know what causes this phenomenon? Talking with friends who usually are up on this sort of thing draws blanks.
posted by captainsohler to computers & internet (14 comments total)

That is pretty weird. I would expect the drive's metal parts to be electrically connected to your computer's case ground (though the shield part of the usb connector). Do you get a similar shock from touching exposed metal parts of the host computer? Is it possible that it's plugged into an outlet with a bad earth ground?
posted by hattifattener at 10:48 PM on August 6, 2008

I'd try the jump-drive on another computer, suspecting that your problem is not with it, but with some grounding issue on your PC.
posted by pompomtom at 11:09 PM on August 6, 2008

hattifattener may have it. You can buy an electrical outlet tester at a hardware store for $5.
posted by sebastienbailard at 11:33 PM on August 6, 2008

upon reading hattifattener's answer I put my finger against the USB drive socket and received a jolt. So, does that mean that I have a grounding issue with my computer? If so, how do I remedy?
posted by captainsohler at 12:11 AM on August 7, 2008

Hmm, looking at the outlet tester that sebastienbailard posted...would the problem be stemming from the surge protector or the main outlet itself?
posted by captainsohler at 12:14 AM on August 7, 2008

You don't have a nylon carpet do you? Is it possible you're charging yourself up and then getting a discharge when you touch exposed metal parts on the computer case?

It's unlikely to be a problem with the surge protector, although that's easy to rule out (plug the PC directly into the outlet).

I think another distinctly possible cause is a grounding problem in the power supply of the PC. If you can source a spare power supply it might be worth swapping it out to see if that helps.
posted by le morte de bea arthur at 2:20 AM on August 7, 2008

There's two basic possibilities. The first is that you're building up a static charge (via nylon carpet, nylon seat, CRT etc) and discharging yourself to ground via the USB socket when you touch it. The way to test this is to touch other metal things that are grounded, like radiators, and see if you get similar electric shocks.

The second possibility is that there's a leakage current from your motherboard and the grounded part of the USB socket, well, isn't, either due to a fault with the USB socket itself, or the PC grounding overall. The USB ground wire is pretty vulnerable and far from the PSU, so that would be my initial suspect.

I have encountered this twice before, where a PC would either give an electric shock, or sometimes shut down instantly when a powered USB device was plugged in. On one occasion it was a faulty power supply, on another occassion it was a fault in the motherboard itself - the front USB sockets were faulty and had a short.

Multimeter's are pretty cheap and useful; you can check various parts of the system internally for grounding problems. Use the continuity section here to test yourself (removing the CPU is overkill, btw) or you can get a PC tech to do for you if needed. You can also test the ground pin on the USB socket in question, and the shield to see if it's grounded.
posted by ArkhanJG at 3:22 AM on August 7, 2008

If it's pulsing with current, that tends to rule out static charges (they dissipate very rapidly). Most likely you have a bad ground in the jump drive's case. I'd unplug it immediately to keep from frying your motherboard.
posted by jenkinsEar at 7:51 AM on August 7, 2008

captainsohler: Either, but I'd guess the outlet itself. I've had a similar "pulsating shock" from stuff plugged into outlets in an old apartment which had had its 2-prong outlets replaced with 3-prong without actually getting a ground wire put in to connect the third prong to anything… le morte's idea seems reasonable to me also, but I would think that a fault in the PC's power supply would only shock you if there were also a problem with the case/earth ground. (After all, the purpose of that case/earth ground is to keep you from being shocked if there's a fault elsewhere in the equipment.)

I second the suggestions of getting a cheap outlet tester and/or a multimeter and doing some probing.
posted by hattifattener at 8:42 AM on August 7, 2008

You shouldnt be able to feel a low 5v current, which is what USB uses. This sounds like a grounding issue. Try plugging the computer into a new outlet and see if you get the same.
posted by damn dirty ape at 9:05 AM on August 7, 2008

You can isolate the problem by trying the jumpdrive in a friend's PC - do you get the same jolt from that? Does this happen if you use it in a different USB socket (not one immediately next door to it, but one a bit away from this socket)?
It sounds to me as if your computer's USB port is not wired correctly (or a power wire on the port connector has come adrift and is occasionally shorting against the case or another wire). The USB port supplies power to peripheral devices -- this is only 5V, but it is DC, which tends to give you a bit of a jolt if touched. Don't use your jumpdrive on this USB socket again if you can help it -- you may damage the drive.
This should be a fairly easy problem to fix, but you need to have your computer examined. If it is still under warranty, I would talk to the supplier/manufacturer. Don't take it into a big box store like BestBuy and avoid Geek Squad if you need to get this seen to yourself -- they are not well known for fixing things cheaply and simply. Find a small, local, computer repair store and ask them to look at the USB power and grounding connections.
posted by Susurration at 9:14 AM on August 7, 2008

It does seem very much like a faulty ground problem. It seems likely that what you are feeling is leakage current (follow the links from old questions for more details, and eventually a technical explanation).
posted by Chuckles at 3:21 PM on August 7, 2008

Removed my cheap ass carpet and the problem is gone for now. Thanks everyone. All of this input has been extreamly helpful. I certainly hope its the carpet because the other avenues seem not as easy to remedy.
posted by captainsohler at 3:41 PM on August 7, 2008

No, its not the carpet. But good to know.
posted by captainsohler at 6:00 PM on August 7, 2008