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Electrocution by Mic

Discussion in 'Sound, Music, and Intercom' started by blademaster, Dec 7, 2005.

  1. blademaster

    blademaster Active Member

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    Hey Guys I heard a few weeks ago about a Texan Pastor that got eletrcouted when either a mic fell into the water or he touched it. I'm wondering what you're guys opinion is on pssible causes as well as whether or not the shure Beta 58 handheld wireless mics could cause the same thing if they were to fall into the water. (i.e. how many amps does a 9v put out at a non-used full current drain)
     
  2. CHScrew

    CHScrew Active Member

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    I think that I heard about that too. I forget exactily how it happened but I know that it did. But I don't know how bad it was though. Did it do damage or was it just a little shock?
     
  3. AVGuyAndy

    AVGuyAndy Active Member

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    First off, to answer the question "Did it do damge?"...the guy died, so yes, it did damage.

    Second, this incident was not caused by phantom power, or power from a wireless mic. In fact, it was a wired mic which he touched.

    Third, the guy was standing in a pool of water. The mic did not fall into the water, he simply touched it.

    Before the incident, the heater in the pool was not working properly, and it was replaced, or repaired or something, and the guy who wired it, didn't do it well.

    The moral of the stroy, make sure your gear is wired properly, and grounded. NEVER use a ground lift adapter if you have a noise problem. Using a ground lift adapter will kill you.
     
  4. blademaster

    blademaster Active Member

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    thanks Andy. how about the other question. If i use a wireless handheld that takes a 9v will the battery getting shortcircuited have the amps to kill a man
     
  5. AVGuyAndy

    AVGuyAndy Active Member

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    Nope, not even close.
     
  6. blademaster

    blademaster Active Member

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    off hand do u know how many amps it does produce being shortcircuited
     
  7. jumpjet

    jumpjet Active Member

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    Typically with no resistance, the amps will just increase to the maximum output of the battery. Ohms law: E= IR, if R is 0, no matter what voltage is, I can go from 0-infinity. That being said, There is a power limitation based on the power equation. P=IE. Without the amount of power neccesary, you will run out of amps. It only takes a tiny bit of current to send the heart into fibrulations(sp) so be careful!
     
  8. Radman

    Radman Well-Known Member

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    That's right, it only takes around 50 milliamps to be fatal, and the fatility is not directly related to voltage.

    Also, never use a multimeter to try and measure the amperage of a battery, something will most likely explode. The amperage rating of a component is what it draws, and the amperage rating of a circuit is the maximum amperage it is designed to withstand. A multimeter measures the amperage being drawn by a component.
     
  9. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Think about it - ever tested a 9V battery by touching the terminals to your tongue? Well that is what shorting it out feels like.

    One of the most important factors in electrocution is resistance. When your skin is dry the resistance is high, when it is wet, the resistance is lower. Those of you that have worked on, or grew up on a farm will know the difference in getting bitten by the electric fence in summer as opposed to winter!

    The other important factor is the ampage (as radman pointed out).

    The 12V ignition coils on some cars actually carry a warning sticker as the amperage that they generate is enough to cause a serious (potentially fatal) shock.

    I got a shock a few months ago from a 240V 16A breaker that had a break in the insulator and suffered nothing more than muscle contractions for the duration of the shock (it actually took a few seconds for me to work out what was happening) and then some general arm soreness for a few hours after. Fortunately, I was sitting on a wooden work bench at the time and my hands were dry.

    I would have to check on the 50mA rating, as I suspect that would be current going directly into the heart (via pacing wires or intra-operatively). I do know that the number of joules used in an open defibrillator is approximately 10% of that delivered externally (with conductive gel pads).
     
  10. Radman

    Radman Well-Known Member

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    30mA across the human heart kills.

    Kindof related.
     
  11. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Interesting reading and supports my comment about resistance of the human body. Interesting that you note 30mA but I could only find reference to 90mA in the calculation put forward here. 100mA appears to be the listed minimum threshold in this and other references.

    Another that I found was: http://www.elec-toolbox.com/Safety/safety.htm which provided a good description of how a GFCI (RCD) works. It also cites a similar lethal current.

    Most of the RCDs that are available here are 35mA rated but you can get them up to 100mA so it would seem strange that these devices would not break the circuit until a lethal current was detected.

    If you look at his calculation for a 9V battery and the average human having a resistance of 500K, you can calculate the required voltage battery required to produce the 100mA shock that is considered to be fatal.

    x = 100mA and 9V = 0.018mA (18 microampares)
    Thus, x = (100 x 9)/0.018 which equals 50,000
    Therefore, you would require a 50,000V shock to be fatal. I think that most stun guns that the police use are 20,000 to 50,000V

    To check, E=IR so 50,000V=I x 500,000ohms
    I=50,000V/500,000ohms, which equals 0.1A (100mA)

    Whilst the math is correct on paper, something doesn’t seem correct to me and I am sure it is more complicated that this. The ability of a power source to actually be capable of delivering the current has to be a factor. I believe that low voltage DC welders have killed people due to the reduced skin resistance form perspiration and the high current at which they operate.

    I have not yet been able to find out the current generated by a defibrillator but I know that 300J to 360J are the standard ‘shocks’ that are delivered during a cardiac arrest.

    Regardless of this fact however is the importance of electrical safety as whilst this debate is interesting, I wonder if people will simply think, “That couldn’t possibly deliver enough current to kill me” when we should be thinking that any electrical device has the potential to cause us harm (even death).
     
  12. Radman

    Radman Well-Known Member

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    According to my latest findings, there is yet another factor involved in this "mystery": the very fabric of time itself! (OK, maybe not the "fabric" part, but the time part, yes.)

    According to this, it takes 1-3 seconds of shock to start fibrillations, which whould then easily explain such high amperages in GFCI's (RCD's), as I believed they are designed to cut off current within a few thousandths of a second. This would be plenty soon enough to avoid fibrillations under most circumstances.

    Another interesting thing is that I remember seeing on the Science Channel (I'm that nerdy) that as a result of earth's magnetic field, there is a constant electrical charge in the air of several thousand volts. It just has such little amperage that it goes completely unnoticed. However, as this is static electricity (I think) I'm not sure exactly how it plays into this discussion. :(

    And with that I submit my findings to the board for your approval. (I'm a scientist today.)
     
  13. jumpjet

    jumpjet Active Member

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    It could have something to do with thermal runaway, as the electrical energy heats up your tissue, it could lower the resistance, allowing more current through...

    In re: the darwin awards thing.

    I really don't think the human body only puts up 100 ohms of resistance. I mean...I could be wrong, but that just sounds FAR too low...
     
  14. Radman

    Radman Well-Known Member

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    If you read closely it says 100 ohms if you take out the skin, as in through a wonderfully conductive liquid that goes to every part of the body: blood.
     
  15. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Actually most RCDs in Australia are 30mA. Those used in hospitals etc are rated to 10mA since persons in those places are more likely to be ill and so less able to sustain the shock. The 100mA units were not designed for protection to human, rather to protect equipment in fault situations. In some cases a main switch in a switchboard will incorporate a 100mA RCD. This is based on what an electrician told me. I believe that where Australians regulations require 30mA RCDs, New Zealand rules mandate 10mA.
     
  16. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Yes you are quite correct and that was a typo on my part. Australian RCDs are available in 10 mA, 15 mA, 30 mA and 100 mA.
     
  17. jumpjet

    jumpjet Active Member

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    I read that, I still think it's low.
     
  18. Radman

    Radman Well-Known Member

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  19. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Nice find Ryan. I think everyone should have a read of that.
     
  20. RonaldBeal

    RonaldBeal Active Member

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    While I don't know all of the details of this particular incident, I suspect a RCD on the audio gear would not have helped. It sounds like the Heater had a short to the water tank. The person becomes the path to ground through the sound system. A RCD on the audio gear would not have tripped, and additionally, if a RCD or circuit breaker was open, it would not interrupt the path to ground.
    A ground lift on the audio gear may actually have saved his life, by not giving the current a path to ground (Still not reccomended practice!)

    Ultimately, the (I suspect) faulty heater DOES need a RCD (or GFCI in the US), and how many of us inspect EVERY peice of eletrical gear we come close to?
     

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