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Posted: Fri Mar 28, 2008 10:42 am
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I did not say it's not possible for you to get a shock, what I am saying is that a properly grounded guitar may still cause an electrical shock if the curcuit it is plugged into is not correctly grounded.
Let's look at this another way. The grounding for your house, there is a metal pole stuck into the ground with a wire attached that goes to the ground side of the electrical box for your house wiring. Now back to the guitar, you have a trem claw screw or bridge post that is stuck into the wood with a wire going to the ground of the guitar electronics. If you remove this wire you are ungrounding the guitar and causing a grounding issue which actually makes you more vulnerable to electrical shock.

To properly shield and ground a guitar the shielding in the pickup cavity should come slightly over the top edge of the cavity, then with the pickguard completely shielded when it is screwed into place the shielding from the cavity comes into contact with the shielding on the pickguard. Now because the pots which are grounded together then to the bridge are attached to the pickguard, the control cavity and pickguard are now part of the grounded curcuit.
If the bridge is not grounded any time you touch the strings (which touch the bridge) and something else electric you have a higher probability of getting shocked because the electrical current does pass through your body.

If you plug your properly grounded guitar into an amp that was built to be properly grounded you still have a properly grounded curcuit consisting of the guitar and the amp. If you plug the amp into an outlet that is grounded correctly you now have a complete curcuit consisting of the building, amp, and guitar. If you plug the amp into a outlet that is not grounded properly the curcuit is not complete and the possibility of getting an electrical shock from your guitar is quite likely.

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Posted: Fri Mar 28, 2008 8:07 pm
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Chet, Thanks so much for hanging in there with me and helping me understand better. When you explained the house ground I understood exactly what you meant. For some reason electronics and electricity confuses me. If you knew me, you would know that I ask simple questions. In my profession, (computer field) I am able to answer the hard questions for my co-workers but my co-workers wonder how is it I can answer hard questions and always seem to ask them easy questions that I should know. They get a kick out of it and they like it because they don't have to answer the hard ones. So here's an easy one for you. If I attach a piece of metal where the spring claw is and ground there is that proper or does my body have to be part the ground.
So far I shielded the routing, output cavities and the pickgaurd and secured the ground wire to the spring claw. I got it correct now right?

Thanks again for having so much patients

BobV


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Posted: Fri Mar 28, 2008 8:51 pm
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You're Welcome. Like I said I am not an electronics whiz, but I had some good teachers. I spent many hours on the phone with my teachers asking the same questions over and over again.
Sounds like your guitar is properly shielded and grounded now.

I'm not quite sure if I understand your question.

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Posted: Mon Mar 31, 2008 3:42 pm
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my question [/If I attach a piece of metal where the spring claw is and ground there is that proper or does my body have to be part the ground. ]

What I'm asking is if I use another source for grounding (ie a conductive peice of metal placed in the cavity where the spring claw is) it would be the same as grounding to a bridge or spring claw and would therefor be properly grounded. It's an isolated ground source as is the bridge or spring claw correct? So doing it this way I isolate myself from the guitars electronis (the strings aren't connected to ground). This doesn't exclude me from possible shock but I believe it reduces my chances of possible shock.

BobV


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Posted: Mon Mar 31, 2008 4:22 pm
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If the bridge/claw are not grounded there is a higher probability of you getting shocked not a lower one.

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Posted: Mon Mar 31, 2008 7:06 pm
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CAFeathers wrote:
If the bridge/claw are not grounded there is a higher probability of you getting shocked not a lower one.


I agree with Chet. As an electrician/electronics tech who has worked with the innards of amps and power distribution inside buildings, the likelihood of receiving a fatal or nonfatal shock through your grounded guitar is very remote. Typically, if there's a short circuit in an amp it'll either blow fuses, trip breakers, or simply not work. As equipment ages, heat and wear and tear can degrade wire insulation. Most dangerous situations arise due to that and excessive moisture, rain, spilled drinks, etc., inside the equipment.

What you may have been be experiencing is static discharge. I remember stepping up to a mic and getting zapped when my lip brushed the metal windscreen. Unpleasant! As a person who's been bitten a few times by 120V AC, I can tell you that it feels quite different than static. I hope to continue to avoid that from now on because I can be lucky for only so long, I do share your concerns about electrocution.

As I see it, you have a few options:

Buy an Acoustic guitar and never use an amp again. Not likely :D, !

Trust the manufacturers and electricians to do their job right.

Avoid using electrical equipment when wet. Playing in a downpour is not a good idea :D ! All bets are off if your amp gets full of water!

Or, use a portable Ground Fault Circuit Interrupter like we use at work to plug in our corded power tools. http://www.watergarden.org/s.nl/it.A/id ... er=froogle

I've never tried one of these on an amp, I assume they would work. These use similar circuitry as the ones in your bathroom and are designed to protect you from electric shock. They also do a good job protecting equipment, because they work faster than a fuse or circuit breaker.

One rule of thumb; If you plug one into the outlet then plug in your equipment and it trips reset it. If it trips again, you may have to call in a pro to figure out if something's bad wrong.

If anyone has tried to use one of these for protecting themselves and their gear, let me know how it worked out.


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Posted: Wed Apr 09, 2008 7:18 am
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Chet has it right, guitars have been grounded in this fashion for many years.

As far as Gibson grounding their bridges, they do, use a multi-meter and check it out. It's just that Gibson's clever at hiding their grounding wire to the bridge.

If your that concerned about your safety get a circuit checker, you can buy on at any home improvemet center for $10. You plug it into the outlet and the led's will light-up and show if there's an issue with the electrical wiring.

There's also a method of installing a capacitor inline with the bridge ground wire that in case of bad grounding, the cap. will blow, breaking the connection.


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Posted: Wed Apr 09, 2008 1:19 pm
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I've been searching the internet on this subject and there are different opinions aout grounding guitars. I will not buy into the claim that manufactures ground the guitar to the bridge because it's the right way. I do lean more towards a cost issue for them. They are covered because hey, they grounded it. For example: I know for a fact that car manufactures build thier cars and release them to dealers for sale knowing that there is a defect in the car. It's more cost efficient for them to fix the problem later after customer complaints or what is called a recall. I used to work with the Volvo engineers so i know this.
Question: When there is a revers ground lets say, is the purpose of the ground wire there so the current disipates to nowhere? ie; a guiatr bridge or say a piece of metal screwed into the guitar cavity? This is where the current should go to right? Now, if I were attached to this ground wouldn't the currect go to me? (being I am now the end of the ground) via the strings?

If I weren't part of the guitar ground connection the current should not go to me right?

This topic needs to be resolved once and for all because I am really confused that there are different opinions about grounding when there should only one correct way to do it without adding the guitar player in the electrical currents path.

BobV 8)


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Posted: Wed Apr 09, 2008 7:00 pm
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The webpage
http://www.guitarnuts.com/wiring/shielding/shield3.php discusses shielding and the issue of getting shocks. A capacitor in series with the guitar's output will protect against DC voltage coming back to the guitar. Here's a quote from that page.

"I've had a few people ask why I specify a 400V capacitor when guitar circuits usually only have a few millivolts on them. The reason is simple, that capacitor is what stands between you (via the grounded strings) and your amplifier. Some vintage tube amps could fail such that they put a potentially lethal DC voltage on the "ground" side of the jack. This type of failure is extremely rare, but why take the chance? The 400V capacitor won't break down like a 35V capacitor would in the admittedly extremely unusual case where you might plug into a "killer" amp. A 250V capacitor is also acceptable as it will probably stand up to 300V or so for at least several seconds. Note that the OEMs don't seem all that worried, most guitars have the strings grounded directly without any isolation. On most guitars, the jack is a non-insulating type which means that the jack plate will be directly connected to the negative side of the jack even after this modification. Metal control knobs may also still be directly connected to the negative side of the jack even with the isolation capacitor in place. Finally, even with the capacitor, a high DC potential failure will give you a nasty "bite" while the capacitor charges – but the capacitor serves to limit the duration and severity of the shock."

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Posted: Thu Apr 10, 2008 5:49 pm
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orvilleowner wrote:
The webpage
http://www.guitarnuts.com/wiring/shielding/shield3.php discusses shielding and the issue of getting shocks. A capacitor in series with the guitar's output will protect against DC voltage coming back to the guitar. Here's a quote from that page.

"I've had a few people ask why I specify a 400V capacitor when guitar circuits usually only have a few millivolts on them. The reason is simple, that capacitor is what stands between you (via the grounded strings) and your amplifier. Some vintage tube amps could fail such that they put a potentially lethal DC voltage on the "ground" side of the jack. This type of failure is extremely rare, but why take the chance? The 400V capacitor won't break down like a 35V capacitor would in the admittedly extremely unusual case where you might plug into a "killer" amp. A 250V capacitor is also acceptable as it will probably stand up to 300V or so for at least several seconds. Note that the OEMs don't seem all that worried, most guitars have the strings grounded directly without any isolation. On most guitars, the jack is a non-insulating type which means that the jack plate will be directly connected to the negative side of the jack even after this modification. Metal control knobs may also still be directly connected to the negative side of the jack even with the isolation capacitor in place. Finally, even with the capacitor, a high DC potential failure will give you a nasty "bite" while the capacitor charges – but the capacitor serves to limit the duration and severity of the shock."


What we have here is a very effective way to prevent getting a shock from a malfunctioning vintage amp as the article says, since caps block DC voltages that are used to power the amp's tubes. They do, however, pass AC voltages and offer little or no protection from an AC shock from a miswired outlet, as also stated in the article near the bottom of the page.

BobV, I know you're really concerned about this so I'll give you an electrician's explanation of why we use fuses, circuit breakers, and GFCIs (Ground Fault Circuit Interrupters).

Fuses and circuit breakers are for equipment and property protection only, which means that if there is a short circuit, the fuse blows or the breaker trips to prevent the equipment from damage, or the building wiring from overheating and possibly starting a fire. They don't act fast enough to prevent a shock to a human being since a 20 amp breaker will trip at a little higher than 20 amps, which is plenty enough to cause us problems.

GFCIs, on the other hand, compare the current coming in from the Hot side (120VAC here in the states) to the current lost though the load and going out through the Neutral side, ~0VAC to see if they add up. If they don't the GFCI trips. It also can detect current loss through the ground wire and trip for that as well. GFCIs usually trip @ >6 milliamps difference which is well below the human body's danger zone for ventricular fibrillation (the heart quivers instead of pumping until we expire :shock: ).

My workplace requires that we use these for personnel protection with any corded power tools in case of a tool malfunction or exposure to wet conditions. That is why they are used near any sinks or outdoor receptacles. Again, I haven't tried using one of these on my gear, but I don't see why it wouldn't work for it.

Hope this helps!


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Posted: Fri Apr 11, 2008 11:34 am
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I like getting bit, it adds to the excitement of the show. ZAP, oh what a feeling. :P


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Posted: Fri Apr 11, 2008 1:23 pm
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Yep, having an EMT perform CPR on a lifeless body does add to the visual excitement of a gig, though it tends to break up the musical flow a bit :lol: !


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Posted: Tue Apr 29, 2008 1:46 pm
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Update!

I was on the TDPRI forum and one of the posters from Great Britain nearly got a fatal 240 volt shock ( that's the Euro voltage, BTW) when he touched a faulty lamp and had his other hand on his grounded guitar. He got a scar on his hand for his trouble and would be in Rock 'n Roll Heaven if he didn't get loose of it. Guys, try not to handle too many electrical devices while holding your guitar, especially if they aren't GFCI protected.

Note: (An RCD is a Brit GFCI)

Quote:

"A long time ago, at a rehearsal in someone's house, I reached up with my right hand to turn on a lamp that had a brass bulb-holder... one of the wires inside must have come loose, because the holder was live. I was holding my guitar neck with the left hand, in contact with the strings. My amp wasn't even switched on but the guitar strings were earthed (grounded) via the lead (cord) through the chassis of the amp. I got a huge 240-volt shock right across my chest from arm to arm and if I hadn't collapsed and broken my hold on the lampholder I wouldn't be around to tell the tale. Nasty and unbelievably scary. As it is I still have a scar on my thumb where the flesh burned and bubbled up.

These days, unless everything is plugged via an RCD I just won't play. I'd sooner lose the gig than my life.
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