Question How can I safely test if I will be shocked when I touch my computer?

[DangWang]

The backstory as to why I'm worried about this and how happened in the first place take a pretty large amount of explaining, so I'd rather not get into it, but, whenever my guitar amp is on and I'm making contact the strings on my guitar and I touch the back of my computer, I would get a shock that was by no means small. I've moved my computer and guitar stuff into a different room, so this may not be an issue anymore, but I'd still rather not take any chances. Is there a way I can test if I'll get shocked if I do what I described above, without hurting myself?

 

[Eximo]

Pretty sure that is typical. A little floating voltage on the guitar. Could also be a ground loop. Is the amp two-prong or three-prong going into the wall? If two prong, maybe add a ground pin and run a wire to the chassis.

If they aren't ever in the same room, I can't imagine you would have a problem anymore. (Insert appropriate arm lengthening joke here)

If you mean to say you have simply moved to a different room, as long as they are on the same circuit this can still happen.

You can test with a volt meter I suppose to be more safe.

 

[DangWang]

Pretty sure that is typical. A little floating voltage on the guitar. Could also be a ground loop. Is the amp two-prong or three-prong going into the wall? If two prong, maybe add a ground pin and run a wire to the chassis.

The amp has three prongs.

If they aren't ever in the same room, I can't imagine you would have a problem anymore. (Insert appropriate arm lengthening joke here)

If you mean to say you have simply moved to a different room, as long as they are on the same circuit this can still happen.

Yeah, I meant that I moved to a different room, and I believe that they're on the same circuit.

You can test with a volt meter I suppose to be more safe.

I've got a multimeter, but I'm not sure which setting to use. I'm assuming it's either DCV or ACV. I'm also unsure as to which prong I should put where. Would one just go on the strings or pickup or something on my guitar, and the other on my computer, or would I need to do something else? I've got very little knowledge in terms of how electricity works and how to do stuff like this.

 

[Eximo]

So you are touching the chassis and peripherals of your computer. That would be ground. You can use any of the grounded surfaces of the computer, which should be everything you can reasonably touch. Most computer peripherals carry metalized paint to act as shielding and a ground plane for safety.

You are touching the strings of the guitar, presumably when it is touching the pickups.

Replicate that, tape the string down or something.

AC voltage will probably be more revealing. Unless the voltage is constant, in which case DC would give an accurate measurement. You really need more advanced equipment to tell what the signal actually looks like.

 

[DangWang]

I put the ground probe on the computer, and the other on the pickups while my amp and everything was on. I tested each setting for both DC and AC, and nothing showed up on my multimeter. I even did the same with the ground probe on my guitar pickup and the other on my PC, just to be sure. Once again, nothing showed up. Does this mean that I'm likely safe?

 

[Eximo]

Should be. Might mean there is improper neutral wire configuration in the other room.

But multimeters typically have at least a 1Mohm resistor in them. And the circuitry itself can absorb some things. So no guarantee.

 

[DangWang]

Just tested it out. No shock!
However, my guitar was in the floor when I made contact with both it and my computer. This wouldn't affect it, would it? In case it matters, my floor is vinyl, and one end of the guitar was also on a rug.

 

[Eximo]

Ground is a confusing term. It is called that because homes usually have a steel rod driven into the actual ground that the main panel's 'ground' is hooked to. Also called Earth. It is more appropriately named Common, as in the common point to define as zero. The intention is that any circuit you accidentally make with your surroundings will have more resistance than the hard wired path to common, so current will flow through that rather than through you. There is a very tenuous connection between your floor and your electrical ground with presumably a very high resistance(vinyl, wood, etc), so that shouldn't have made a huge difference.

What happens in a ground loop is that one or more circuits has the hot and neutral lines swapped, and one of the circuits which would normally have no circuitry on the neutral line, does, because it is backwards. This puts a load on the neutral line. And in many circuit designs, neutral will be tied to common. So you effectively have current flowing through ground.

I've run into this many times with various power supplies (like amps), or just having long cable runs next to other electrical equipment. That was more an induced current in nearby wires though. Still the solution was to tie the commons together. Which says something may not be quite right in that first room.