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Ground the bridge or not?

Discussion in 'Pickups & Electronics [BG]' started by KramerDon, Nov 5, 2013.


  1. Phalex

    Phalex Semper Gumby Supporting Member

    Oct 3, 2006
    G.R. MI
    Ground it!
     
  2. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    I never bother...
     
  3. khutch

    khutch Praise Harp

    Aug 20, 2011
    suburban Chicago
    You really think your hand won't tighten in a death grip around metal control knobs or an amp cable connector housing? I sure would not bet my life on that!!! If your venue's wiring is unsafe then all kinds of metal on stage is deadly. You don't want to play in that venue. A GFI will safe the equipment you plug into it but your next of kin will find out the hard way that something you never suspected punched your ticket out of here.
     
  4. megafiddle

    megafiddle

    May 25, 2011
    24 gauge wire will carry 29 amps for 10 seconds before melting.

    http://en.wikipedia.org/wiki/American_wire_gauge

    The fatal current level through the heart is less than an amp. I've seen it reported as low as 0.2 amp.
    There is a current gradient through the body during an electrical shock though. Not all the current is
    through the heart. But even lower currents can have serious effects. Everyone reacts differently.

    A missing ground is all you need to allow the amp chassis to float up to some voltage through power
    transformer winding to core capacitance, or the "grounding cap" in older amps. Add a short in the amp
    and a swapped neutral and ground, and you can have full 120VAC on the chassis (and bass).
    Not likely, and even less likely to occur all at once, but all those faults have occured.

    -
     
  5. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    you could ground the bridge through a 250 mA fuse, which will likely pop before anything bad happens (or even for no good reason at all).

    you could also ground through like a 1μF cap, so as to drain off the noise while blocking DC shocks.

    or you could just connect the bridge to ground normally like everybody else does and has done for almost a century now without a second thought.
     
  6. megafiddle

    megafiddle

    May 25, 2011
    I would go with the 3rd one.

    Just about every appliance with a metal enclosure or cabinet has the exposed metal grounded.
    Grounding is what makes appliances and basses safe.

    The danger is the same as with kitchens and bathrooms - the presence of a good ground.
    Water pipes are obviously not dangerous, and neither is a grounded bass. It's the "other stuff"
    in proximity, the things with ground faults that are the problem.

    A fuse probably wouldn't work anyway. I believe many electrocutions are not from high current,
    but from sustained low currents.

    -
     
  7. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    That ground wire is generally soldered to a pot. That solder joint will get hot and melt before the wire does. Regardless the chances of an electrocution from a bad ground on a bass guitar is less than getting stuck by lightning, winning the lottery and getting bit by a shark.
     
  8. megafiddle

    megafiddle

    May 25, 2011
    Nope. that solder joint is sitting on a relatively huge heat sink (the pot case).

    I agree, the chances are very small, judjing by the number of instances.

    -
     
  9. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    Exactly there are just to many fail safes, like amp fuses, circuit breakers and ground circuits.

    I have been hit by a 277 volt lighting circuit at the plant I work at. It hurt but it didn't almost kill me. While less than an amp can kill, it is very rare that a shock from a 120v wall circuit is fatal.
     
  10. megafiddle

    megafiddle

    May 25, 2011
    Me also. I work on live 480VAC 3 phase. I've never found myself across two poles, (480V),
    but came in contact with one pole while grounded a couple times (277V to ground).
    The shocks were painful. I don't know how typical I am, but I know another who wound up
    in the hospital with a similar shock. Fortunately, I don't get nervous and sweat around that
    stuff. That would significantly lower skin resistance.

    I also always position myself so that if anything happens, I will fall away from the voltage
    source. If you fall onto it, even if 120V, you are probably finished.

    -
     
  11. Exactly right! In my years of electrical work I've known two other electricians killed by electrocution.One by 277V and one by 120V both got hung up with no one around to help.A GFI will protect you but by the time a 20A breaker trips,you're gonna be dead if the shock path is thru your heart or brain.The shock factors are voltage,current,time and path thru the body.
    I've also never gotten across 2 phases of 480V but 277V hurts bad and I've been fortunate to only have gotten that across my hand or from my hand to elbow a few times.
    Are you IBEW by chance? Local153 here
     
  12. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars

    That's exactly how it got me. I didn't think 277 hurt any more than 120. The only time I got shocked to where it was painful was from the 120v DC battery backup system for the DCS at work.
     
  13. funnyfingers

    funnyfingers

    Nov 27, 2005
  14. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    If you want to go that route you can just use a fuse inside your bass, in the bridge wire. No reason for a resistor and a wristband.
     
  15. khutch

    khutch Praise Harp

    Aug 20, 2011
    suburban Chicago
    Well, we are trying to do the same thing as the safety resistor inside an OSHA approved anti-static wrist strap, for the sake of those who worry about a grounded bridge. I'm guessing that a fuse will not blow fast enough to protect your heart from fibrillation. The wrist strap is for people who want to play tapewounds and coated strings. Personally I would go with a grounded conductive tape strip up the back of the neck over a wrist strap. And I would not bother with a resistor.
     
  16. In one of my first electronics courses we were told it is 0.1 to 0.2 amp. That is what this page says also.
     
  17. megafiddle

    megafiddle

    May 25, 2011
    No, not IBEW. Just do industrial electrical work (plastic extruders).

    I caught the 277 while one hand was on ground and the other was on the pole.
    Just contact, not actually grabbing anything, else I'd likely not be typing this.
    You just don't go near it unless you have an escape plan.

    -
     
  18. I was going to suggest the fuse, but you beat me to it.
    Fuse: No noise added, safety for you paranoid dudes. Win!
     
  19. Been there done that. I believe most houses are grounded by connecting to a water pipe witch goes into the literal ground.So if your in the basement near said pipe yes you can short out that circuit and that doesn't feel too good.
    So now I ground my guitars by using a 1/4 watt resistor to the bridge.
    __________________
    damn barefoot kids and their music
     
  20. Wow! What a lot of, uhm, interesting opinions here.

    Any "you are going to die" statements about 120 AC current are comical. "It could possibly kill you" is perfectly reasonable. Thus the electricians here who both know it can kill them and yet have been shocked by it (and by 277v legs - ouch). "You are going to die" is a ridiculously definitive exaggeration. If it wasn't, there wouldn't be so many of us who have experienced such a shock.

    Yes, a wall socket ground can be hot, and it can be hot with full current available, and without blowing any circuit protection. All it takes is two flaws to both happen at the same time: a hot wire shorted to that ground wire, and the ground wire not being connected to a ground path. Anyone who thinks such things could not happen hasn't seen the horrors of what the ignorant can do when they start messing with wiring.

    Houses are grounded to a long copper stake driven into the ground. Your water pipes are usually connected to this ground as well. Yes, a grounded bass is just about as dangerous as your kitchen or bathroom faucet - less so: it less likely to contribute to you drowning or slipping.

    If a grounded bridge was a genuine health hazard (to any degree of reasonable concern) you can bet that there wouldn't be a single manufacturer grounding their bridges, because they all would have been sued into oblivion by the families of all those dead musicians.
     

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