[SOLVED] Why was I getting shocked when coming into contact with my computer?

[DangWang]

I've seen a few other threads asking a similar question, but in those threads, it seemed that the shock was happening whenever someone came into contact with their computer. For me, I was only shocked when I was using my guitar, which was plugged into an amp that was on. I never have been shocked in any other situation. Something similar happened when I tried to plug my amp into my computer via USB. (the amp has USB capabilities that allow settings to be modified, so there shouldn't have been any problems with this.) As soon as the USB touched the computer, there was a pop, which leads me to believe that it shorted or something. (my knowledge of electricity is very little, please bear with me) After this the computer seemed to be fine. I thought that the issue was the cord, as I was using one that didn't work too well, so I tossed it and got a new one. This time, however, the amp was not plugged in to an outlet, and when I plugged it into the computer, everything was fine. As soon as I started to plug the amp in, (to a surge protector that was off, might I add) there was another pop, and I believe that blew a fuse, and probably did my computer in, being the idiot that I am.
So, with that all being said, what happened? I've read in some other threads that it could be due to improper grounding, but, if that was the case, I would be shocked whenever I made contact with it, right? I'd also like to add that a few weeks ago, my basement, where my computer was, flooded, and one of the things that got wet was my computer. After opening it up at least a week after the event, everything seemed fine, and it worked properly. Could that have anything to do with it?
If any more information would help in answering this, I'll do my best to supply it. Any help would be greatly appreciated.

 

[Grobe]

There could be one or several of this issues:

• Earth fault to the computer (very likely since it have being in contact with water)
• Earth fault to the amp.
• Earth fault at another location (behaviour will depend on what kind of net your power company is providing).

 

[DangWang]

There could be one or several of this issues:

• Earth fault to the computer (very likely since it have being in contact with water)
• Earth fault to the amp.
• Earth fault at another location (behaviour will depend on what kind of net your power company is providing).

By "earth fault to the computer ", you mean that the problem was with the computer and not the outlet it was plugged in to, correct?

 

[Grobe]

What I mean is that there may be a current path between one live phase to ground. Where that path is located I cannot possible know, and you'll probably get "shocked" at touch regardless.

 

[Csib1337]

Human body can build up current. That's why We use esd protection. If your body is charged and you touch the Mobo it can cause serious problems. If you use Esd equipment, gloves, bracer etc your body is grounded and it protect your circuits in your pc. Hope its an answser for you mate.

Ui: like other mates said It could be false grounding also or some "current" traveling around like in power poles sometimes current traveling around point less. If you touch the pole it can give you a nice shock.

 

[Grobe]

Human body can build up current

No, that is totally wrong!
The only known component able to store actual current is electrical coills.

An human body can store a certain amount of electrical charge. However I have never heard an electrical discharge of a human making an actual popping sound

 

[Paperdoc]

Since this happens when you connect the guitar AMP and the computer, and gives a substantial current flow that blows a fuse, I have to suspect either the wiring of the amp or the wall outlet it is plugged into. You do not think you are skilled in electricity, so I suggest you get a qualified electrician or tech to inspect the amp and the wall outlet. What I suspect is that somewhere there is a reversed set of wires making the Hot and Neutral connections backwards.

This could happen if the power cord into the amp was done wrong. The way the wires of its power cord are connected inside the case to the amplifier must match the way the wires are connected to the plug prongs. There's also another possibility. For plugs with only TWO prongs, current designs have them with different widths so they can only plug into modern outlets one way (see below). But if you use an older two-prong plug with prongs the SAME width, it is possible to plug it in the wrong way. The amp still works by itself, but there is a big problem when you try to connect it to another electrical device, like your computer.

It also could happen if the wiring to the wall outlet was wrong. That latter case is NOT common. But there is a way it can happen without being noticed. Several decades ago in older houses the wires in the wall were only TWO leads - Hot and Neutral - and all the wall outlets had only TWO vertical slots in them of the same size. When the in-wall wiring was installed, little attention was paid to which slot got which wire, because all the plugs could be pushed in turned either way, and there was no way to enforce a polarity distinction. Later house wiring systems changed to using THREE wires (Hot, Neutral and bare Ground) and outlets with three holes. On one of those, if you have it installed so the round Ground hole is at the BOTTOM of the triangluar pattern, then the vertical slot to the RIGHT is always HOT, and the slot to the LEFT is always NEUTRAL. Moreover, the Neutral slot is taller, and on the plug on the end of a cord, the one prong also is wider so that you can only plug that into the outlet one way. Of course, with 3-prong plugs there's only one way. But even with 2-prong plugs, there is only one way because the prongs are different widths.

Where a problem can arise, though, is if someone tries to do a conversion and gets it wrong. One way is to replace the old 2-slot outlet in the wall with a 3-hole new outlet, but NOT replace the in-wall wiring. First this means you do NOT have a true Ground on that outlet. But worse, if you get the two power lines hooked up wrong (and the wires themselves have no identification), the outlet has the Hot and Neutral slots reversed! Dangerous! For that reason, doing this kind of "upgrade" is illegal.

These problems can be detected and fixed by someone with the right skills, but it's not easy for an amateur to learn how and be confident of doing it correctly.

 

[Grobe]

One more thing.

Where I live, it doesn't help being "skilled". At here, only licenced electricans are allowed to do any changes at any electrical installations.

That means - if you do something with the electrical installation, and then sometime after, an accident happens (i.e. house burn down), then the insurance company may hold back and refuse insurance money to rebuild house.

You should check the rules for that where you live.

 

[Paperdoc]

Grobe is right. Although an unlicensed person may have the skills to do the job well, that's not good enough for some authority organizations. I do some of these things myself. But technically where I am, two things are required. I'm not sure whether the work MUST be done by a licensed tradesman. At one time that was not required, but maybe that has changed. In addition, the work needs to be inspected and approved by an inspection agency before the device can by put into use. And almost all insurance companies will insist that their fire insurances is in effect ONLY if ALL of the electrical wiring in the structure HAS been approved and a certificate for that is available to prove it.

 

[DangWang]

This could happen if the power cord into the amp was done wrong. The way the wires of its power cord are connected inside the case to the amplifier must match the way the wires are connected to the plug prongs. There's also another possibility. For plugs with only TWO prongs, current designs have them with different widths so they can only plug into modern outlets one way (see below). But if you use an older two-prong plug with prongs the SAME width, it is possible to plug it in the wrong way. The amp still works by itself, but there is a big problem when you try to connect it to another electrical device, like your computer.

In the first half of the paragraph, you're saying that, if the situation is that, the problem is because the amplifier is wired incorrectly, correct?
Also, in the latter half of the paragraph, I'm understanding that that could only happen with plugs with only two prongs, correct? I know that both the computer and the amplifier had plugs with three prongs, so that couldn't happen, right?

Where a problem can arise, though, is if someone tries to do a conversion and gets it wrong. One way is to replace the old 2-slot outlet in the wall with a 3-hole new outlet, but NOT replace the in-wall wiring. First this means you do NOT have a true Ground on that outlet. But worse, if you get the two power lines hooked up wrong (and the wires themselves have no identification), the outlet has the Hot and Neutral slots reversed! Dangerous! For that reason, doing this kind of "upgrade" is illegal.

From what I'm taking from this, I believe this could be the situation. All almost all of the other outlets in this level of my house are two pronged outlets, the exceptions (that I am aware of) being two that were installed five or six years ago, both of which are on the same fuse, a separate one from the other outlets on this level, and the one I had my computer hooked up to, which has the same outlet cover and is on the same fuse as the rest of the outlets up here, which leads me to believe that it was, as you described, at some point changed to have three holes, and the wiring was not changed. If this really is the situation, would everything have worked fine until the amp and computer were connected? Or should there have been problems as soon as I plugged in the computer? Also, not sure if it matters, but the computer was also plugged into a surge protector, instead of being plugged directly into the wall.

 

[Paperdoc]

First part, the amp wiring. It is still possible for the wiring of the amp's power cord to have been done wrong even when it came with a 3-prong plug. However, that is quite unlikely - amp makers know how to wire it properly and don't make such an error. And where is the guitar amp with the 3-prong plug plugged in? Into the the outlet box with 3-prong outlets and a cover that looks different?

It is much more likely that a "conversion" of wall outlets from two-prong to three-prong was done wrong. But I think I'm missing a couple details, so let me be sure. In that room are mostly 2-prong outlets in the walls. But there are two outlets with 3-prong sockets, and at least one of them (the one your computer is plugged into) has an outlet cover exactly the same as all the 2-prong ones, right? That would indicate that that particular outlet box had its outlet fixture replaced but the old cover re-used - normal procedure. So at least that one outlet MAY have been wired wrong. Since you don't claim expertise in this area, I am NOT recommending you investigate and change anything yourself. But I will explain a little just FYI. If the old 2-prong outlet fixture in the box was replaced with a 3-prong fixture, there is a 50% chance the polarity of the new outlet fixture is backwards. That is because both the wires into the box from the fuse panel look identical - both black covers - and it is not obvious which one is Hot. That question can be determined with some simple tests by someone who knows how, but I do not suggest you try it.

IF that "conversion" was done the simple (and incorrect) way, there still is NO bare Ground wire coming into that outlet box. So, even though the new 3-prong fixture in the box has a Ground (round) hole, there actually is NO Ground connection there at all. That makes your Surge Protector likely useless. The very common way a Surge Protector is designed is that there are two small devices called MOV's inside. Each is connected between the Ground line and either the Hot or Neutral line. What each does is provide a possible short circuit path between one line (say, Hot in one case) and Ground. An MOV acts like a very high resistance so no real current runs though it normally. But at some high voltage (a voltage surge on the line) it suddenly becomes a very LOW resistance and acts like a short circuit. This causes an overload of the fuse back in the panel and that shuts off the power to the entire circuit until the fuse is replaced. HOWEVER, this action also destroys the MOV - it is sacrificed for this one event. From then on you have NO surge protection on that line, even though the multiple outlets on that box work. Often people don't even know that their surge protector is not working any more after one successful protection event.

Now, it is also POSSIBLE that the "conversion" was done correctly. The fact that you have in that room ONE outlet box containing a 3-prong outlet that appears different suggests that it was added at another time. So MAYBE when that addition was done, a new proper cable was run all the way from the fuse box (NOT just from another room outlet box) that contains all three lines - Hot (Black), Neutral (White) and Ground (bare). That would make it possible to connect that one outlet box correctly. THEN, if that was done, the person doing the job MIGHT also have done a similar re-wiring of the second outlet box that has a 3-prong outlet fixture (the one your computer is plugged into). IF BOTH boxes were properly re-wired from the fuse box with new cable, and IF the connections in each case were done correctly, then you do not have a wall wiring issue. Otherwise you certainly CAN have incorrect connections causing your problem.

If the "conversions" were done the simple and incorrect way, that may NOT have caused any obvious problem before. Most consumer equipment is supposed to be wired so that the outer accessible parts are NOT connected to either the Hot or the Neutral line. So even if the wall outlet polarities are reversed, you should NOT make any contact with an electrically "live" part and never know of the wiring mistake. However, if you try to make connections between two different user devices (say, your computer and your amp) that are plugged into different outlets that happen to be wired differently, the Ground (outer shielding of cables) can become a connection path between Hot in one outlet and Neutral on another, causing a major problem like shocks and blowing fuses.

 

[DangWang]

Whoops! Sorry about the super late response.

However, that is quite unlikely - amp makers know how to wire it properly and don't make such an error. And where is the guitar amp with the 3-prong plug plugged in? Into the the outlet box with 3-prong outlets and a cover that looks different?

The amp is plugged into a surge protector, which is plugged into the outlet with a different cover, which is newer than the other outlets in the room.

From then on you have NO surge protection on that line, even though the multiple outlets on that box work. Often people don't even know that their surge protector is not working any more after one successful protection event.

Is there any way that I can test whether or not my surge protector is still working as it should? I've not got much of a clue as to how long I've had it, and it wouldn't surprise me if the MOV has been used.

THEN, if that was done, the person doing the job MIGHT also have done a similar re-wiring of the second outlet box that has a 3-prong outlet fixture (the one your computer is plugged into). IF BOTH boxes were properly re-wired from the fuse box with new cable, and IF the connections in each case were done correctly, then you do not have a wall wiring issue.

To my knowledge, the person who did the wiring for the more recently added outlet wouldn't have changed anything with the other outlets in this room. The older 3-prong outlet, the one my computer is plugged into, was like that when I moved here, and the newer outlet, the one my amp is plugged into, was added after I moved here, by a professional electrician, so I know that one should have been done correctly, and I'd assumed that he wouldn't have changed anything about the other outlets in the room unless it was necessary.

I'd also like to mention that I'm now using a different computer, one that doesn't have any problems with it, unless it came from the factory faulty in some way. The amp was covered by a warranty, so I've got the exact same model. I bring this up because, just to make sure that I wasn't in any sort of danger playing guitar while my PC is on, I touched the chassis of my new computer. No shock. Thought I was competently fine, until today, when I touched the back of the computer, instead of the chassis, (I've got problems controlling my "what if I..." impulses) and got a nasty shock. Turns out that the chassis isn't metal. This makes me nearly positive, and very hopeful, that it's a problem with the wiring of one of the outlets in my room. I'll hopefully be moving my computer and guitar stuff back into my basement, where I shouldn't have any problem, unless water's screwed up the power outlets down there, or the problem up in my room doesn't have to do with the outlets. Once I've got my stuff back in the basement, is there any good way that check if it would be dangerous to make contact with my computer while I'm using my guitar, without harming myself, or anything else? I tend to get paranoid about stuff about this, so it'd be nice to know whether or not I could injure myself when I move everything, or if I need to separate my computer from my guitar so I don't accidentally bring about my untimely demise.

Thanks for the response, and, once again, sorry about my late response.

 

[Paperdoc]

O can suggest a couple of ways to check things.

1. You can buy fairly inexpensive outlet checker tools that you simply plug into an outlet and examine the lights that glow. They come with a set of patterns to tell you what problem is found, or none. However, most of these are for Grounded THREE-prong outlets, and you may not be able to use them to test an outlet with only two slots.

2. If you get get a relatively simple digital voltmeter or multi-meter you can use that to test for voltages. For your reference point you need a 3-prong (Grounded) outlet you are confident is wired correctly, and use one of its ROUND Ground holes - NOT either of the flat slots. As an alternative, IF you can reach easily the cold water metal pipe entering your basement just before your water meter, that's usually a solid Ground. So ONE lead from the voltmeter goes there, and the meter should be set to read in VOLTS. If the meter is of the auto-ranging type, just let it set its own range but look at exactly what it says so you know whether you're reading volts or millivolts or something else. If you have to set the voltage range, start with a high range and then switch down to more sensitive if it shows zero volts. Use the meter's other probe to touch various places, starting with the outer case of your computer (or whatever). So, compared to Ground you should always find zero volts on any surface you can touch easily. Now, absolutely zero volts may not be what you get on the MOST sensitive range, depending on how sensitive your meter is. But certainly you should NOT see anything over 10 or 20 millivolts (mV). FYI, even 10 Volts applied across a human body is not dangerous - a car battery is 12 VDC, and you can put two fingers across its terminals and feel nothing. BUT any part of a computer or amp or guitar or whatever that you CAN touch easily should NOT have anything like that kind of Voltage on it. If it does, there is something wrong with the way it is connected.

 

[mortemas]

Shocks from guitar amps are not unheard of (just google guitar amp shock, you’ll get plenty of results). Try plugging the amp and the computer into the same outlet instead of different ones. Having said that, you should still remain cautious and take the sound advice of others and do some testing to determine if there is anything wrong with your AC mains outlets.