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I'm getting shocked! Electricity grounding with 2-prong?

  1. Apr 26, 2010 #1
    Hi,

    My main question is how to ground a 2-prong if the electrical utility originally was a 3-prong, but the grounder fell off?

    The story is that I went to this new music studio and played the electric guitar while singing in the mic. The mic shocked me. I guess something wasn't properly grounded. not sure of exact physics.

    And this got me thinking, because next week I'm playing an outside gig, and we're using a piano amp as the amplifier for the vocals. and this piano amp originally had a 3-prong cord, but the grounder fell off, and so it's just a 2-prong cord now. (this would mean that it's not grounded i guess)
    So, If I'm singing through this, and playing the electric guitar at the same time, I'm guessing that the mic would shock me again. would it?

    so, how could i ground this?

    thanks
     
  2. jcsd
  3. Apr 27, 2010 #2
    Get used to it. This usually means that the mixer isn't grounded properly. It happens a lot in the biz, and you should really just get used to it. It's usually just a nuisance, but BE CAREFUL: it can be deadly sometimes. Note that the singer from Stone The Crows was killed by a badly grounded system.

    As for your particular case, you're correct. The Piano amp is NOT grounded properly and probably shouldn't be plugged in without the third prong.

    However, if you have your heart set on playing with that amp, then I guess you can. You may get small shocks, but it shouldn't be anything big. KNOW THAT YOU USE THAT AMP AT YOUR OWN RISK!

    Your best bet is to take the amp to an amp store/repair shop or even just get an electrician to replace the plug, it will make sure that it's grounded properly and you can stay safe.
     
  4. Apr 27, 2010 #3

    sophiecentaur

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    To be honest, you will only get a shock if the equipment is actually faulty. Proper Earthing will carry fault current to Earth and save you from an actual shock but there is no reason why you should get a shock from an unearthed device if there are no paths from the supply live to the case or microphone ground.
    A proper Power Supply Unit will isolate the LV Electronics from the high voltage Mains. Even when there are valves involved there is no excuse.
    It is a problem at gigs where you have to use other people's equipment, of course. If your system is fairly uncomplicated then you should get it checked out for not much money.

    An isolating transformer in a supply can remove a lot of the dangers - but they are a bit expensive. I seem to remember the BBC used to supply Bands via isolating transformers. Equipment that is constantly being thrown around in the back of vans is more at risk than static equipment.
     
  5. Apr 27, 2010 #4

    russ_watters

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    Get someone to re-wire the plug.
     
  6. Apr 27, 2010 #5

    sophiecentaur

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    Not a bad idea.
     
  7. Apr 27, 2010 #6
    Isn't the third prong there incase the live wire gets loose and touches the device's case. So if you touch the device you will not getting shocked as the third prong will create a short allow the current to flow through. That is what I always thought the third prong was for :S.
     
  8. Apr 27, 2010 #7

    turbo

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    Do NOT "get used to it" or you may soon be an ex-musician. The plug must be replaced by someone that knows what they are doing. Do not use that amp again until it is repaired. That means not just attaching a plug with a ground prong on it, but also maintaining the polarity of the two flat prongs.

    If you went to a music studio and got shocked, either the owner of the studio hasn't grounded his equipment properly or the receptacles were installed improperly WRT polarity. OR, you brought your own guitar amp and that was plugged in ungrounded or with reverse polarity. Never use an ungrounded amplifier, either for vocals or instruments.

    I can't tell you how many guitar amps I have seen with the ground lug missing from the plug. When I was running open-mic jams weekly, I'd look over every amp that people brought in, and if they weren't properly grounded, I didn't allow them to be used. I usually had a spare amp around, and would let them use that. Ungrounded musical equipment is a hazard to everyone near it, not just the person playing through it. Remember that your guitar is shielded through the amp's ground, and that your metal bridge and strings are connected to that ground. What's going to happen if you touch another guitarist whose amp is running on reverse polarity to your amp? Bzzt! The dangers are greatly magnified if you are playing while standing on soil or concrete.

    If you happen to own an older amp that did not come with a ground lug, you really must get a competent repair-person to replace the power-cord. If you own an older Fender that has a "hum" switch, get your repair person to disable it. It flips the polarity of the amp's power-supply, and once you have a properly installed grounded power cord, that is unnecessary and potentially dangerous.
     
  9. Apr 27, 2010 #8

    OmCheeto

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    Yours is the correct answer.

    The removal of the ground prong with subsequent "shocks" indicates a faulty circuit. The circuit should be fixed, and then the 3 prong plug should be replaced.



    Om, electrical safety inspector, USN, 1978-1983
     
  10. Apr 27, 2010 #9

    Borek

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    I wonder, where is the ground when you are under water...
     
  11. Apr 27, 2010 #10

    OmCheeto

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    I'm sure somewhere there was a pile of dirt with a 6 foot long copper rod buried in it. Though for the life of me, I don't remember ever seeing it. It must have been under the battery.
     
  12. Apr 27, 2010 #11

    mgb_phys

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    Musicians/studios are notorious for removing the ground pin from equipment as a 'quick and easy' solution to ground loops.

    That must limit the range of operations slightly ( I think Borek was referring to the N part of USN)
     
    Last edited: Apr 27, 2010
  13. Apr 27, 2010 #12

    Borek

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    Please, Borek, not Borak nor Borat :grumpy:
     
  14. Apr 27, 2010 #13

    turbo

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    Pass the horse-urine beverage, please. :tongue:
     
  15. Apr 27, 2010 #14

    mgb_phys

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    Sorry typo (result of typing one handed on a tablet with a coffee in the other hand)

    ps. I understand how you want to keep your film career separate - avoid the paparazzi and so on, hence the disguise.
     
  16. Apr 27, 2010 #15

    OmCheeto

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    From the sounds of the scope of this problem, I'm starting to think that maybe the nerds purposely design the equipment to kill musicians. They do after all, get their money for nothing, and their chicks for free.
     
  17. Apr 27, 2010 #16

    turbo

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    Musicians who are scraping by and playing dives would often snap the ground lug off the plug when they had to play in a place that was wired long ago. Even worse, there was a long gap in the US when receptacles were not polarized, and the plugs on old amps had power lugs of the same size. This presented some dangerous situations. It is not surprising that amp technicians called Fender's "hum switch" the "death switch", since you could be working next to another musician whose amp/instrument setup was quieter with a polarity exactly opposite to yours. Not good.

    BTW, for any musician with an urge to re-wire their own amps, please reconsider. Especially with older tube amps. You will need to replace zip-cord with fat 3-conductor cords, which means that you'll need a heavy reamer to enlarge the holes that the power cords enter through. You'll need the press-in restraints that hold the cord, and protect the cord's insulation from abrasion so that the conductors in the cord don't contact the chassis of the amp. Most of all, you'll need some smarts to figure out when some amp is designed in a way that can be very dangerous to the user when you touch switches or try to replace fuses. Fender was very bad at these things, though their amps were popular.
     
  18. Apr 27, 2010 #17
    You still have to get used to it, as a solid 10-15% of the places you play will shock you, from THEIR mixers and so forth...
     
  19. Apr 27, 2010 #18
    It might be wise to (make repairs and) avoid unsafe situations?
     
  20. Apr 27, 2010 #19

    mgb_phys

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    Or form a 50s rock tribute band and all wear crepe soled shoes?
     
  21. Apr 27, 2010 #20

    DaveC426913

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    For Pete's Sake yes, get it fixed.

    I'll make it easy. http://xkcd.com/730/" [Broken].
     
    Last edited by a moderator: May 4, 2017
  22. Apr 28, 2010 #21

    sophiecentaur

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    "Polarity" has nothing to do with it. The way Line and Neutral happen to be connected will make no difference whatsoever to the situation in properly working equipment. The reason that the line and neutral should be connected correctly is that there is less possibility of shock if there happens to be a fault in the equipment - i.e. a path from a part of the circuit at high voltage to ground. Both live and neutral should, in any case, be isolated by the power supply circuitry (transformer) from the equipment ground / Earth and from any other equipment that may be connected.
    What is very important, however, is that the line and neutral of the actual supply should not be reversed (i.e. the polarity must be preserved through any distribution leads and splitters). This is so that any fuse will be in the live leg of the supply and can be relied upon to cut mains volts from further downstream when it blows. If the fuse turns up in the neutral leg, the current will be interrupted but parts of the equipment will still be live even though the equipment is nominally 'disconnected'.
    A residual current circuit breaker will always prevent any more than an annoying, slight shock, and will refuse to turn on if there is any (>a few mA) leakage to ground.

    If the same rules applied to electronic musical equipment as are applied to 'site' equipment, then no one would tamper with their own gear and safety would be much improved. I would go so far as to say that anyone who doesn't appreciate what has been written on this thread and who can't distinguish the correct from the incorrect information shouldn't be let anywhere near a screwdriver and wire cutters. I should have thought that the terms of insurance for public events would be scary enough to discourage ignorant tampering . . . .
     
  23. Apr 28, 2010 #22

    turbo

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    That is incorrect and it is dangerous misinformation. In grounded amps, the ground is tied to neutral. If the receptacle your amp is plugged into was wired improperly, the amp's chassis will be referenced to "hot" not "neutral". If you are using an older amp with a "hum" switch, it is used to switch your amp's ground reference between "hot" and "neutral". This is very common on Fender tube amps. My favorite little tube amp is a Fender Vibro Champ with an un-grounded and non-polarized plug (both prongs the same size). I have taped a tiny diagram to the plug to make sure that I always plug it in with proper polarity at home, and I NEVER played out with it.

    Mix-and-match polarity on stage or in the studio (regardless of cause) is dangerous. If you're a guitarist and you get crossed up with a "hot" mic or come in contact with another guitarist or bassist with improperly grounded or polarity-referenced gear, you can get significant, even deadly shocks. There is a reason that professional musicians' amp-techs re-wire Fender fuse-holders and disable hum-switches (death switches) - protecting the lives of the musicians that they work for.

    For any posters here that doubt the veracity of my information, head out to a Borders or other big book store, and browse Dave Funk's "Tube Amp Workbook", Aspen Pitman's "The Tube Amp Book", or any of Gerald Weber's excellent books on guitar amplifiers. These authors cannot afford to get it wrong, for liability reasons at a minimum.

    If you are a musician, you owe it to yourself to learn enough about electrical safety to know when you are out of your league and need expert advice, so you'll seek appropriate service from people who know what they're doing. Not from posters on on-line forums with no service experience.

    And remember, if you are counting on a fuse to save you from a fatal shock, your heart can stop before the fuse blows, especially if some wing-nut has replaced the amp's fuse with one of a higher value and/or a slower "blow-time". Another reminder: When you are playing electric guitar, your picking and fretting fingers are at the same ground potential as your amp. Your guitar is ground-referenced through the ring-connection of your guitar cord to the chassis of your amp. If you touch something that is not at that same ground potential, some current will flow. If it's a little, you may not notice. If it's a lot, it can kill you.
     
    Last edited: Apr 28, 2010
  24. Apr 28, 2010 #23

    Averagesupernova

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    So what happens when this amp is plugged into a GFCI outlet?
     
  25. Apr 28, 2010 #24

    turbo

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    Your point is??? Have you ever played in a club when the receptacles on the stage were CFGI's. I have been playing music for over 40 years and have never encountered one.

    Your deflection of this topic is not relevant.
     
  26. Apr 28, 2010 #25

    dlgoff

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    I have had first hand experience with this situation while playing in bands. I've even experienced this where home owners put in their own circuits where switches are wired to switch of the neutral, leaving the device hot. Good way to see a few sparks.
     
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