Hi guys, ok I'm rather alarmed by this, was just plugging in my external USB HDD and I got a little zap when I touch the Earth metallic part of the USB plug. Tapping the USB plug to the metallic ports on the back of the computer causes little visible blue sparks.

I seem to recall that things that are not properly grounded and running a current through the air can slowly ruin the components of your PC in a deteriorative way over time.

What's really concerning is that my previous PC was acting strangely and now I am upgrading and just about to plug that drive in, and just had the thought, what if that external USB drive has been slowly killing my PC? I don't want my new upgrade to suffer the same fate.

FYI; I set my multimeter to test DC voltage and put the red probe on the USB earth and the black probe on the earth back of the PC and I got a steady -10 mV

 

Hi guys, ok I'm rather alarmed by this, was just plugging in my external USB HDD and I got a little zap when I touch the Earth metallic part of the USB plug. Tapping the USB plug to the metallic ports on the back of the computer causes little visible blue sparks.

I seem to recall that things that are not properly grounded and running a current through the air can slowly ruin the components of your PC in a deteriorative way over time.

What's really concerning is that my previous PC was acting strangely and now I am upgrading and just about to plug that drive in, and just had the thought, what if that external USB drive has been slowly killing my PC? I don't want my new upgrade to suffer the same fate.

FYI; I set my multimeter to test DC voltage and put the red probe on the USB earth and the black probe on the earth back of the PC and I got a steady -10 mV

Try measuring AC. Does the drive have an external power supply?

 

You are on the right track. Change tour meter to AC and measure it again. Chances are you will see a higher voltage.

If you don't see a voltage, it may be static electricity buildup in your body - especially if you see this zapping happening with USB sticks or USB-powered HDDs. In this case, a change in environmental conditions is required - carpets, fleece coats, etc may be causing this buildup.

 

Is it static electricity, such as when you scrub your socks across the carpet then get one good zap out of it, or if you sit there tapping the usb plug against the case does it spark continually? If it's static, then not a lot you can do about that except grab something grounded before you touch your PC. If it's continual, then check the neutral and ground on your wall outlet. The USB shielding and computer case will be connected to ground, which would be connected to the ground in your wall outlet through your computer plug. If the outlet is wired wrong then you can get voltage where it should be 0V.

 

It sounds a little as though your PC. P.S. does not have the L.V. power supply common conductor connected to the service earth ground as it should be.
Or that your power cord is not connected to earth properly.
Max.

 

Is it static electricity, such as when you scrub your socks across the carpet then get one good zap out of it, or if you sit there tapping the usb plug against the case does it spark continually? If it's static, then not a lot you can do about that except grab something grounded before you touch your PC. If it's continual, then check the neutral and ground on your wall outlet. The USB shielding and computer case will be connected to ground, which would be connected to the ground in your wall outlet through your computer plug. If the outlet is wired wrong then you can get voltage where it should be 0V.

Agreed. And in addition to the quoted comment, assuming all things are grounded properly plugging in your USB HDD isn't going to harm either the USB or the computer. Just touch the metal part of the USB and touch the computer frame (not painted surface) and if it IS static discharge, you'll equalize the charges of both USB and computer. Then when you plug the USB into the computer there won't be any spark at all.

Interesting story (true): My house, when I bought it, I plugged the computer into one outlet and the printer into another. The previous owner installed three pronged outlets and directly connected neutral to the ground terminal as well. So both neutral and ground were common on the plug. In the basement (I assume) a wire must have been broken. So it was reconnected (without the benefit of a box) Black to White and White to Black, thus reversing the hot and neutral. So in the plug where the printer was connected its voltages were wired correctly, but the computer, instead of being "case ground" it was "case hot". When I plugged the printer cable into the back of the computer, the grounded wire of the printer cable touched what was case hot and burned a hole through the back of the computer case. Boy was I angry!

Anyway, the first thing that came to mind when I read your question was static electricity. This time of year, the cold weather brings dry air. Static electricity in cold dry air is much worse than in warm humid air. Chances are good all you are experiencing is static discharge; the static that is generated by you moving through the house or office.

 

It sounds a little as though your PC. P.S. does not have the L.V. power supply common conductor connected to the service earth ground as it should be.
Or that your power cord is not connected to earth properly.
Max.

I have to agree with Max on this one and my thinking runs with:

Tapping the USB plug to the metallic ports on the back of the computer causes little visible blue sparks.

If this was just a static discharge I would expect a spark but tapping and getting sparks lends me to believe there is a potential difference between the PC ground and external HDD USB other than a static build up. I would look at things with the meter set to measure AC volts and see what there is.

I just bought a new external USB HDD for a friend and unlike my several years old Western Digital 500 GB drive which uses an external power supply the new ones I looked at were all powered off the USB port directly. The USB port shells on all of my PCs are at earth ground and the USP port shell of my older WD drive is same. I would also wonder if the thread starter has both PC and external HDD plugged into the same outlet?

Ron

 

I have found a lot of power bricks have a capacitive filter across the mains, with it connected to the 0V output. And if the 0V out is not earthed via the power lead (a lot only use 2 pin plug), then you have half the supply volts at the output. It is at fairly high impedance but can still give you a bight.

 

The first thing that I would suggest checking is that wall wart that powers the external drive. Some of those are JUNK. What to check for with the meter is for a voltage from the negative side of the connector to both the ground side of your outlet and also to the neutral side of the outlet. What it seems like is that there is a connection from the mains to the output on the external power supply. And there should not be any connection. It is probably a 12 volt supply and it should be easy to get a replacement. But be careful with the polarity on the power connector of the replacement, some are center negative, instant destruction for some devices.

 

I'm under the assumption the TS is complaining of the initial contact with the spark. If this sparks every time you touch it to the case then it's not static. What I mean is if you tap tap tap it and you get a spark every time. Tapping it every half second and you get a spark then it's not static. But my original assumption was 'Hey! This happens every time I plug it in' meaning plugging it in today then walking away and coming back to plug it in again and another spark. Static in that case.

 

In commercial products that meet safety ratings the values of these "Y" capacitors are limited by the RMS line current that can pass through them. From memory for most consumer products this is about 500 microamps. Yes, it is pretty irritating. I don't know whether it is a good idea, but I added a ground connection to my computer to drain off this current and keep USB near ground so that when I touch stuff on my bench connected to USB I don't "do the dance".

 

The best way to get a really good shock is to be well grounded! That way there is a path for the shock current to take when you touch some live wire. Of course, with much higher voltages they may find a path to ground adequate to deliver a shock, but for normal mains voltages that is seldom the case.
And if you get sparks between the USB plug shield and the computer housing then certainly there is some problem with the power source of that external drive. An external drive should be completely isolated from the mains, and as you are getting sparks that you can see that is not the case. So before making that connection you need to solve the problem. AND use your meter on both AC and DC to check for a voltage difference. You may indeed need to get a different wall wart to power the external drive.

 

Hi guys, ok I'm rather alarmed by this, was just plugging in my external USB HDD and I got a little zap when I touch the Earth metallic part of the USB plug. Tapping the USB plug to the metallic ports on the back of the computer causes little visible blue sparks.

I seem to recall that things that are not properly grounded and running a current through the air can slowly ruin the components of your PC in a deteriorative way over time.

What's really concerning is that my previous PC was acting strangely and now I am upgrading and just about to plug that drive in, and just had the thought, what if that external USB drive has been slowly killing my PC? I don't want my new upgrade to suffer the same fate.

FYI; I set my multimeter to test DC voltage and put the red probe on the USB earth and the black probe on the earth back of the PC and I got a steady -10 mV

Hello there,

Wow, that does not sound like static electricity because that's usually just one or two sparks and is not repeatable over very short time periods in most cases.

What you could do is try to reverse the connection to the power supply AC input by turning the plug upside down. If that helps, then you have a bad wall wart.

Another possibility is that you have the PC plugged into one outlet and the Drive plugged into another outlet and they are on separate circuits which also happen to be on opposite sides of the AC transformer/line that feeds your house or office. In that case make sure they are both plugged into the same outlet.

 

Guys I recorded a video to prove its not static electrcity, showing the sparks it generates, and how the multimeter displays 88v AC and -10v DC. Edit: after recording the video, I noticed my powered USB hub's USB plug shows the same sparks, though not as much and doesn't sting when I touch it. I get 77v AC and -8v DC when testing the same way as in the video.

Try measuring AC. Does the drive have an external power supply?

Yes it has it's own power supply, that's what makes me think the internals are not grounded properly. I guess that small fact was omitted and everyone thinks it's one of those small unpowered HDDs. Sorry.

Anyway, the first thing that came to mind when I read your question was static electricity. This time of year, the cold weather brings dry air. Static electricity in cold dry air is much worse than in warm humid air. Chances are good all you are experiencing is static discharge; the static that is generated by you moving through the house or office.

(FYI I'm in Australia, middle of summer) definitely not static electricity, it's a constant buzz and sting rather than a momentary zap, and I can repeatedly produce sparks by tapping it to the back of the computer case. I can also sting myself with it by touching it to the metal leg of the desk and the touch the leg of the desk with my finger.

I know it's a small current because I have an old CRT TV that does this too (which I'm getting rid of) and I have 2 newer CRTs that don't have this problem . It feels totally different than static electricity guys, there's definitely a small current. But my main concern is if it will fry my PC components slowly over time.

 

Hey everyone, there have been a lot of replies since I initially drafted up that post and finally recorded the video this evening and uploaded it. I'm just off to bed right now. I'm sorry if I didn't directly address everyone's reply but I will be checking this thread very carefully in the morning.

. I would also wonder if the thread starter has both PC and external HDD plugged into the same outlet?

Ron

Yes I do, they are both on the same powerboard from the same wall outlet. Edit: and so is the powered USB hub I mentioned earlier.

 

I once had voltage appear on the headphone socket of a crt TV. I only found out when I had headphones on and touched the radiator at the side of me, got quite an unpleasant tingle. I emailed the manufacturer but heard nothing back.

 

...I'm in Australia, middle of summer) definitely not static electricity, it's a constant buzz and sting rather than a momentary zap...

Experienced something similar. Touching a grounded drill collar (14 inch diameter for oil wells) and touching the rivet on an outlet at the same time I discovered 68VAC. The drill collars have electronics in them, and there was a device that would test fine but then when installed into the collar it would blow out. The cause was the computer that was hooked to the board during installation. There was a ground fault on the power cord going to the computer allowing an induced 68 volts between the computer and actual ground. Now that you've explained your situation I must agree, it's not static but rather probably a ground problem.

 

I don't know whether it is a good idea, but I added a ground connection to my computer to drain off this current and keep USB near ground so that when I touch stuff on my bench connected to USB I don't "do the dance".

Surely this should be in place already, all the Desk Top/Tower PC's I have ever owned had the case and P.S. DC common connected to earth ground.
Also Definitely points to the OP not have this in place.
My USB HDD is powered off the PC, so there is no separate wall-wart etc.
Max.

 

OK, and after seeing the video and those meter readings it is clear that something is not at all right. So the first thing that I suggest is checking the desktop computer unplugged and verifying good continuity between the computer frame and the line cord ground pin. Then you will be able to know where the fault does NOT lie. Also check between each of the computer line power pins and the computer frame, switch ON, cord unplugged. Those should show open. Then a similar test with your external hard drive and power supply, if it has a ground pin, and also the line pins. And last, check the connections inside the powerboard, with it unplugged but switched on. What is obvious is that it is a real problem just as you describe. If those checks do not reveal the cause then it is time to investigate a bit farther. I have a guess but nothing solid to back it up with yet.

 

My money is on the PS for the external HD, many of these have SMPS and usually do not have a earth ground pin on the socket.
Max.