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Basses Mics Amps and Electric Shocks (any electricians in the house?)

Discussion in 'Miscellaneous [BG]' started by theshadow2001, Jul 19, 2007.


  1. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    So I was practising in my drummers shed a while ago and got some mild shocks of a mic I was "singing" into. Chances are I was touching my bass at the time I'm not quite sure though.

    Anyhow I really want to know what causes these shocks.

    People say that it's bad grounding in of the outlet or possibly amp/pa. When something beomes live and isn't grounded and you touch it you become the path to ground and get a shock. However this sounds like something that would cause more serious electrical shock rather than the milder shocks I experienced.

    The other thing is when you touch a mic and bass you ground some current thats coming from the mic through your yourself then the bass then the amps ground connection. Or vice versa.

    However I can't see why current should appear on the metal parts of the mic (or bass) for me to help on its way to ground. Is there some sort of leakage somewhere? Or is there voltage being induced somewhere on the circuit that it shouldn't be?

    If everythings wired right I'm pretty sure that if there was no ground on anything you still shouldn't get a shock as the ground is a safety feature just in case anything funny happens (metallic parts become live for instance). So where does the voltage come from?

    Could there be a problem further back in the wiring with a neutral somehow causing current to appear on the earth.

    Can anyone explain exactly whats going on when you get these shocks and how to find out whats causing them and how to remedy the matter. If Im getting mild shocks I think there's potential for something more serious to happen.
     
  2. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    I guess some things man is just not meant to know.

    Perhaps this would be better in the amps forum where there would be more tech heads
     
  3. dave_p

    dave_p

    Dec 20, 2005
    CT
    it boils down to different potentials. the amps ground may not be at the same potential as the mics ground. or the polarity mat be opposite. try having both on the same strip, or flip the polarity on one or the other.

    i also used to get mild zappage playing while on a damp cement floor in bare feet.
     
  4. IanStephenson

    IanStephenson UnRegistered User

    Apr 8, 2006
    Does it happen places other than the shed? Could be bad wiring in the shed, or in any of the equipment.

    At the very least I'd invest in an RCD - £10 from any DIY store. It'll stop an ouch turning into a emergency, by shutting down the power before you get fried. If it trips out other than VERY rarely, then you've got a signifigant problem that needs looked at properly.

    Ian
     
  5. It happens quite regularly.

    Try changing to a different socket, its a bad ground as you suggested, and as mentioned, its a case of different potentials.
     
  6. eedre

    eedre

    Feb 26, 2007
    St. Louis,MO
    Mild shocks may mean your PA amp isn't grounded well.

    I used to use an old (circa 50's) Fender Super Reverb as a PA. I had some zaps that stood my hair up. I recently disassembled the amplifier on it (for other reasons) and found out that the power cord on the old amp didn't even have a ground lead. No ground at all! A two-prong plug. Easy fix, no problem.
     
  7. Isn't this how Keith Relf died?

    Ken.
     
  8. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    Well there's no such thing as polarity reversal here. We've been using three prongers for decades. The funny thing is everything was run from one socket in the garage. Three amps and the PA (The availabilty of other sockets is limited. So Basically my amp my bass and the mic were all connected on the one circuit. Which is kind of weird when I think about it that I was getting shocks. Since everything had the same earth. Maybe the multitap was faulty.

    Also is having grounds at different potentials enough to drive the current that gives you that little zap?
     
  9. Trevor.A

    Trevor.A

    Jan 2, 2005
    Lubbock, TX
    One of the outlets in my room isn't grounded, so the strings shock you if the amp is plugged into it. It's not very powerful, but makes playing for any amount of time almost impossible :meh:
     
  10. Steve

    Steve

    Aug 10, 2001
    If everything is correct, you won't get shocked.

    The fact that you ARE getting shocked indicates that something is not correct.

    The fact that you are only getting mildly shocked is good fortune and my not always be that way. There are a lot of variables that determine how hard you get hit.

    Why it's happening could be a bunch of things. Check all your grounds and make sure that no AC polarity is reversed in the system for a start.

    I didn't stay at a Holiday Inn last night but I am a master electrician.:D
     
  11. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    I'd be interested if you expanded a lot on this statement
     
  12. Johnny Crab

    Johnny Crab ACME,QSC,Fame/Hondo/Greco/HELIX user & BOSE Abuser Gold Supporting Member

    Feb 11, 2004
    South Texas
    Greetings from south Texas!
    NOT an electrician by trade,
    do have electrical engineering degree.

    Get one of these for cheap:
    VOM.

    Set it to AC Volts.
    Touch one lead to your strings and one lead to the PA gear metal(mic stand, mic, etc.). MAKE SURE YOUR HANDS ARE NOT CONTACTING THE METAL LEAD TIPS. If you read ANY voltage, something ain't right and needs to get fixed. This can get you killed if you have one hand on your bass and put the other(sweaty or not) hand onto a micstand/etc...and viola! You get AC current from one hand to the other across your heart muscle....

    In the USA, we have GFCI(Ground Fault Current Interrupt) outlets and circuit breakers. I'm not sure of the Ireland equivalent. They are supposed to trip when a very small current "leaks" from one circuit to another. They trip in the milliamp range but they do not fix any pre-existing problem. It sounds like in your case, some of the current was either "leaking" from the PA through you to your amp's circuit or vice-versa.

    Possible causes:
    Faulty ground or not low resistance ground and the micstand on the earth or concrete slab(grounded) and some leakage voltage from your amp -> you and the micstand are an easier path to ground.

    Neutral or GROUND with voltage on it...if you didn't wire the place yourself or verify the wiring...I've seen voltage on neutrals and voltage on "grounds" and I've found faulty grounding at the primary/main disconnect(feed in from the power co. transformer) in one case.

    If you can't yourself, I would get EVERYTHING checked out.

    Electricity is nice but must be used safely.

    Got a HUGE zap at 8 or 9 years old when barefoot on damp cement floor and squeezed the metal "ON" button on a soldering iron. After working on and seeing internal wiring in many Marshall's, Fenders, SVT's, and other electrical devices....you could NOT pay me enough to play barefoot on a damp concrete floor with a cable. Wireless yes. Wired no.
     
  13. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    I feel like a bit of an idiot but im just after realising the drummer used one of those german power leads for the PA. Its a two pronger that can be stuck into our standard sockets with a bit of resourcefulness (for the want of a better word) In other words no ground connection.

    Which means that my bass and amp provided a nice easy path to ground for the current. The question remains though why is there current in the first place? Does indicate that the PA is faulty somehow?

    I'd imagine but can't be sure that there's an RCD (GFCI for the americans) on the garage socket. However the leakage was probably a lot less than the 30mA needed to trip them. Since its only a a small zap. 30mA would be a much more substantial shock than that I believe.

    Edit: because a two pronger is used there could be polarity reversal as well. What effects will that have?
     
  14. Steve

    Steve

    Aug 10, 2001
    It will have the effect of quite possibly giving you mild shocks. Especially if your amp is does not have the polarity reversed.

    A modern American style 2 prong plug is not that much of an issue because on prong is slightly wider and can't be put into a receptacle backwards.

    Foreign equivalents I can't comment on.
    Older (like maybe 15 or more years) American 2 prong plugs can be inserted backwards and cause polarity reversal.

    You need to first verify the integrity of the grounding system in the shed by checking all the receptacles to make sure a ground is present and the connection is tight at all the receptacles.

    While you're doing that look at all the receptacles and make certain that the black wires are under the gold colored screw and the white wires are under the silver colored screws. The ground wires should be without insulation and under green colored screws.

    You can swap black and white wires on a receptacle and it will still work but the polarity wil be reversed.

    There is also a great little cube type tester that can be had at any home depot or decent hardware store generally called a "circuit analizer" or "plug tester" (duh!) that does a great job of testing for proper wiring and only costs maybe $10.

    I just realized you are in Ireland so much of what I just posted may not even apply to how things are done. I know a good chunk of Europe is ungrounded power with 220 volts on one wire whereas it takes 2 wires to get 220 in the US. Also much of Europe uses a black wire as the designated "earth" color.

    You need an irish electrician to confirm.
     
  15. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    How does this happen?

    I used to build electrical panels so I have a some knowledge of electricity and what a good connection looks like (although I'm an industrial engineer never studied electricity as in depth as electricians or electrical eng)

    Brown is live blue is neutral and green/yellow for earth here.

    I've meant to get one of those testers before but I never thought about it since I'm not playing out much.

    While having good ground connections is important what I really want to know is how can current be leaking to ground (or through me when none is present) Whats causing that current to flow somewhere it reallly shouldn't be flowing (to ground)
     
  16. Steve

    Steve

    Aug 10, 2001
    The thing you have to get your mind around is this:

    The blue wire and the Green wire are connected together at the source.

    The brown wire is your source voltage, the other two are your return path back to the source.

    The blue wire is intended to carry current back to the source, the green wire is a safety to keep all the non current carrying metal parts "as one" electrically.

    If you reverse polarity on an amp you put source voltage on what should be the non current carrying metal parts and the brown wire becomes the return path.

    So, you grab a bass where the metal is + and you put your lips on a mic from another amp where the metal is -.

    Exactly how much that hurts depends on how good of an electrical conductor you happen to be at the time. The human body is generaly a pretty poor conductor but a little sweat, maybe some water and you can become a very good conductor.

    Electricity only "prefers" to take the path of least resistance. It'll take what it can get even if it's you
     

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