Just got shocked by something in my studio

[clntgn]

Let me start of by saying that this is the second time I've experienced electric shock due to equipment, so I have a little knowledge. As I'm typing this my arm hurts.

So, I was sitting and writing something in my room, playing guitar, and once I was finished I decided to record it. I turned on my recording computer which had been in sleep mode for awhile (so my audio interface which is bus powered was still on). And I unplugged my headphones from one audio interface to the other. Nothing wrong with that. I pick up my guitar again, and then I reach up to my interface to jiggle the headphones (has a tendency to play out of one ear sometimes), and I feel the familiar vibrating sensation down my arm. I of course immediately pull away, go and wake up someone to make sure I'm able to safely turn off all my audio equipment without killing myself, and then unplug everything.

Now, I've got a safe bet as to what the cause was. I have a very old 60s tube amp that I got at some guitar thing. I had my uncle give it to someone he knows to repair, UNFORTUNATELY, much to my chagrin, no one replaced the plug, which is a 2-prong ungrounded deal.

So, a few questions:
-Is the rest of my gear going to be alright?
-Is it possible to replace the plug relatively cheap?
-Is there any other parts of my amp that could cause this?
-Is my amp going to be ok (I love the tone on this amp)

And I'm fairly certain I'm going to be ok. As I've said before, this happened one other time, but that was in high school with the school's crappy equipment.

 

[dintymoore]

I have an old tube amp and the guy before me put a 3 prong power cable on it (I wouldn't have chosen bright orange), but it doesn't look like it was a difficult thing to do. There's others here who have more experience with that though.

I'd unplug the guitar amp and see if the rest of the gear is fine. It probably is. You're not the first to get zapped by an old tube amp.

I bought a tester like this for about $15, they sell them at most hardware stores:

You can use it to test your outlets to see if they are wired correctly.

I also bought a cheap Sears $15 multimeter. You can use one to see if a surface is hot and there's times when I've done that - it beats touching something to find out.

Most modern gear has fuse protection that makes shocks way less common than with old tube amps. Old tube amps are notorious for giving you shocks. You gotta love those all metal power switches! I put rubber automotive vacuum caps on my toggle switches.

 

[clntgn]

I just want to know why it happened when I was holding my guitar and reaching to grab my headphones.

The last time I got shocked was from a much larger, solid state keyboard amp. It was actually between two amps, grabbing two cables one from each amp in each hand. That was a lot more scary though, because I was stuck in a circuit.

I honestly don't know why they didn't replace the cable too. My uncle assured me it'd be fine, but I guess it wasn't. I'll probably just stave off using it until I have the money to get the plug replaced.

 

[WhiteStrat]

When I was a kid (13 or 14) I had an old tube amp (yep, two prong electrical plug), and once I sat down on the window sill (it was summer, and we had no air conditioning, so the windows were open) and our windows had a metal lining. Shocked the shit out of my ass.

I ran down to tell my dad, and he didn't believe me. So I brought down my guitar and amp, had him strap it on like a rock star--then had him touch a metal heat vent--guess what? he got the same shock.

His advice? Sell the amp. Bad advice, dad...I wish I had that one back...

 

[cyrano]

I bought a tester like this for about $15, they sell them at most hardware stores:

That's OK to check if the wiring is connected as it should be, but it doesn't check the earth connection.

I also bought a cheap Sears $15 multimeter. You can use one to see if a surface is hot and there's times when I've done that - it beats touching something to find out.

Don't trust a multimeter for that. If a metal surface on your gear is "hot" you'd better check the earth connection of your electrical system. To do that reliably, you need what's called a "megger". It's a kind of mini generator that produces 500 - 1.000 V and measures if it can flow down to earth correctly. If this sounds like mumbo jumbo, have it done by a certified electrician.

Most modern gear has fuse protection that makes shocks way less common than with old tube amps. Old tube amps are notorious for giving you shocks. You gotta love those all metal power switches! I put rubber automotive vacuum caps on my toggle switches.

The fuse in the amp is there to protect the amp, not the user. You could easily die without the fuse blowing.

You should have a "diff switch" in your electrical system. It's a device that constantly measures if the current going through one wire als passes through the other wire. If the difference between these two currents is above 30 mA, the diff will switch off and protect you. If there's a difference between these two currents, it's leaking to earth, which is OK, unless it is leaking through your body...

And yes, it's a long rant, but a very close friend died because of a setup where people considered having a working earth connection wasn't important. It's still very common with light and PA setups. Very few people seem to understand the importance of a well working earth connection.

 

[PDP]

When I had a two prong tube amp and got shocked I turned the plug around changing the ac polarity. That always seemed to work.

 

[dintymoore]

That's OK to check if the wiring is connected as it should be, but it doesn't check the earth connection...

The tester I posted does test if the outlet is grounded.

You can test if something is hot with a mutimeter.

cyrano have you checked to see if the fuse box is properly grounded.

I have to say cyrano that you are coming off like a know-it-all that knows very little. Why are you asking such basic questions if you know the answers to advanced questions?

 

[cyrano]

The tester I posted does test if the outlet is grounded.

It doesn't. It just shows if an earth wire is present and if the wiring is OK. It doesn't show if the resistance to earth is low enough to take the current from a failure in equipment. Why do you think a certified tech uses a megger and not that tester?

You can test if something is hot with a mutimeter.

You can't. You can attach one testprobe to the equipment, but where will you place the other? You could measure resistance between one side of the mains supply and the metal chassis or box, but even that doesn't mean the equipment is safe. OTOH if that resistance is low, you know it is not safe. At best, it is an indication, not a test.

cyrano have you checked to see if the fuse box is properly grounded.

Sorry, maybe I misunderstood. Are you referring to the fuse box in the electrical system? I was thinking about a fuse in some equipment. I thought you were talking about an amp...

But anyway, fuses will only blow AFTER you 're dead. 30 mA can kill. 30 mA will not blow the fuse.

I have to say cyrano that you are coming off like a know-it-all that knows very little. Why are you asking such basic questions if you know the answers to advanced questions?

I wasn't asking any questions. I was just concerned. Every year, a number of people die because people rely on the wrong tools. I was equally careless with electricity until my friend died. And the only thing wrong with the setup was that it had no earth connection. He was just adjusting some lights. Everything was hooked up in a professional manner, except the earth connection. Diffs were present, earth was connected but the resistance to earth was way to high.

Most studio gear is DC, low voltage and doesn't carry that risk. But lighting equipment, power amps and other "heavy" gear should be earthed well. And old tube guitar amps are a prime example of potentially dangerous gear for two reasons: they carry a higher voltage than the mains supply and the isolation can be slowly decaying because of age. They might be "hot" today, they could be lethal tomorrow.

I know cutting corners is sometimes the only solution if you're on the road cause you can't simply install an earth connection. All too often there's no time. But, at least, be aware of the danger involved and adhere to the old electrician's rules: never work on a wet or even a damp floor, wear shoes with rubber soles and keep one hand in your pocket.

 

[dintymoore]

... You can attach one testprobe to the equipment, but where will you place the other?

To a known to be good ground, and it will show you if there is current. Either that or you can start grabbing stuff like clntgn did but my method doesn't mess my hair up.

What I'd do for starters is go to the fuse box and test the continuity from there to the main house ground.

None of it's too hard, you can do it all with a simple $10 multimeter, I've wired houses from the ground up and it's not rocket science.

 

[cyrano]

To a known to be good ground, and it will show you if there is current. Either that or you can start grabbing stuff like clntgn did but my method doesn't mess my hair up.

What I'd do for starters is go to the fuse box and test the continuity from there to the main house ground.

None of it's too hard, you can do it all with a simple $10 multimeter, I've wired houses from the ground up and it's not rocket science.

I'm seeing your point now. Only, how will an average person with an even less than average understanding of electricity know the earth connection is OK?

You clearly understand what it's about. But I'd hate to see that average person running out to the store and buying a multimeter and then trying to figure out if it's safe.

As I'm typing this my arm hurts.

I'm reading this as being on the edge of safe...

 

[Opivy]

wow! Never knew that could happen -

I remember a few years back - there was this one outlet in my house that didn't agree with my friends amp. (it was a fender blonde - umm type tube amp? not sure about the exacts)

but the strings on the guitar would electrocute your fingers. It wasn't unbareable - but painful enough that you wouldn't want to play it.

How's that happen?

 

[clntgn]

Ok, well, I'd rather not die, but my dad certainly knows a lot more about electronics than I do. I went to college for composing music, not fixing amps and instruments. So I think I'll have him check out all this stuff. He's replaced the plugs on amps before, so I trust him at least a little. I'll show him this forum and have him read over it. Hopefully he can make sense of it, because as cyrano said, I really don't understand a lot of this.

I have another amp I can use in the meantime, but its also much bigger, and although the tone is great, its also kind of loud.

 

[austinm08]

I've experienced this, too! Except it's happened to me when I have my electric guitar strapped and on me and I go to grab a microphone... it's happened more than once at different places. If I'm touching the strings and touch a microphone in the right place it shocks me!

 

[frederic]

The tester I posted does test if the outlet is grounded.

Actually, it doesn't.

It checks that the ground of the outlet is connected to the neutral buss/ground bar in the breaker box as is correct, but it doesn't check if there is an earth ground - which is different - that's the connection from the box to the earth - either through a cold water pipe or a stake driven into the earth.

In mis-wired houses, "ground" in the outlet can easily be a measurable voltage above earth, even if the wiring to and from the breakerbox and outlets is code-legal and spot-on.

Seen it many times.

 

[dintymoore]

Electricity always finds the least resistance path to ground, and if your amp isn't grounded correctly you can become that path.

I would think a three prong plug with the ground attached to the amp's metal chassis would be a good place to start.

I would still get one of those outlet testers and test your outlets. I carry one to gigs. I've had times when there are two outlets and I could use either, and my tester revealed that one was grounded properly and the other one wasn't. There's no way you could tell that by looking and gear would appear to work in either.

 

[dintymoore]

Actually, it doesn't.

It checks that the ground of the outlet is connected to the neutral buss/ground bar in the breaker box as is correct, but it doesn't check if there is an earth ground - which is different - that's the connection from the box to the earth - either through a cold water pipe or a stake driven into the earth.

In mis-wired houses, "ground" in the outlet can easily be a measurable voltage above earth, even if the wiring to and from the breakerbox and outlets is code-legal and spot-on.

Seen it many times.

Yes, you are correct. To see if the ground is actually good you'd need to go to the fuse box and see if the ground is good there. My main reason for pointing out that tester is that it's something someone with no experience can use and it does give you some "better than nothing" info. Lots of people are freaked out about opening their fuse box, and rightfully so if you aren't experienced in the dangers.

Very often you would have to put a 10 page response to posts if you wanted to include all the pertinent info, thus quick generalizations with "errors".

 

[clntgn]

According to my dad, the house we live in doesn't have a fuse box. We live in a housing development, our house was built within the last ten years, and I don't think I've ever had a problem with that outlet, nor the surge protector I was plugged into.

Before we go ahead and replace the plug, are there any specifics we should know when messing around with that sort of thing? My dad has done this before, but on a much newer amp. I don't know how much the technology has differed.

 

[witzendoz]

Is you Dad and Electrician? if not he should not be changing plugs. The problem could also be that the earth to your room has lifted. You need to test the outlet to check it is earthed.

Even if you don't have a fuse box so to speak there will be a circuit breaker box for you house between the electric meter and the outlet.

If you are unsure call in an electrician, especially if the problem only happens in your house, it could save your life.

Cheers
Alan.

 

[clntgn]

My dad is not a certified electrician, but he does have a lot of experience, although I am still a little unsure about it, so I'm going to consult an electrician I know from church if I can get in contact with him.

Now, I have a surge protector plugged into the wall outlet. The surge protector has two lights on it, one says "protected" the other says "not grounded". The light that says protected is lit up currently. Is this roughly the same as what you mean when checking to see if the outlet is grounded?

 

[witzendoz]

Your surge protector is saying what I am thinking, there is no mains earth for some reason. Could it be the surge protector thats at fault.

The problem with somebody working on mains power who is not an electrician is that if there is a death from something they wire up they will probably end up in jail. Even if they have a license, and they wire incorrectly they will end up in jail. It's called manslaughter.

The fact that you are getting shocks and that your dad has experience does not compute, his experience should be that you leave it unplugged and call an electrician.

Sorry to sound serious but electricity is serious.

Alan.