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

  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. 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. sophiecentaur

    sophiecentaur 13,699
    Science Advisor
    Gold Member

    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. russ_watters

    Staff: Mentor

    Get someone to re-wire the plug.
     
  6. sophiecentaur

    sophiecentaur 13,699
    Science Advisor
    Gold Member

    Not a bad idea.
     
  7. 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. turbo

    turbo 7,366
    Gold Member

    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. OmCheeto

    OmCheeto 2,078
    Gold Member
    2014 Award

    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. Borek

    Staff: Mentor

    I wonder, where is the ground when you are under water...
     
  11. OmCheeto

    OmCheeto 2,078
    Gold Member
    2014 Award

    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. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    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. Borek

    Staff: Mentor

    Please, Borek, not Borak nor Borat :grumpy:
     
  14. turbo

    turbo 7,366
    Gold Member

    Pass the horse-urine beverage, please. :tongue:
     
  15. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    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. OmCheeto

    OmCheeto 2,078
    Gold Member
    2014 Award

    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. turbo

    turbo 7,366
    Gold Member

    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. 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. It might be wise to (make repairs and) avoid unsafe situations?
     
  20. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    Or form a 50s rock tribute band and all wear crepe soled shoes?
     
  21. DaveC426913

    DaveC426913 16,226
    Gold Member

Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?