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Voltage safety

  1. May 14, 2007 #1
    Hi everybody,

    I have a question concerning a "stupid" thing i did today. I found a electric multimeter (if it is called so- you know, the device that measures dc current, the resistance in Ohms, dc and rms of ac voltage...), and thought to measure my body resistance. I didn't even think that any current you cross my body, so i checked it. I held the "+" and the "-" of the multimeter with each of my hand

    I was part of this close circuit for about 4 seconds when my right hand started feeling a bit weird. So i closed the multimeter. The fact is that for about 4 hours now my right hand is a bit numb. I don't think that this is anything serious, but I would like to know how much current ran through my body.

    As i checked, the multimeter has a 1,5V or 2x1,5V battery, and for the second that I looked at it, the resistance of my body seemed to be around 0.8 M-Ohm. So probably the current was too small, but do you know exactly how most multimeters operate. Is it safe to check like this your body resistance?

    That's all.

    Last edited: May 14, 2007
  2. jcsd
  3. May 14, 2007 #2


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    I've done it hundreds of times.
  4. May 14, 2007 #3
    That's just normal. I sometimes do it as a way to test if the VOA works (in stead of short cut the probes). My body's resistance is about 1-5M-Ohm. That value depends on how wet your hands are and the sweat of your body as well.
    For some special kinds of ohm meter, they use high voltage to measure very high resistance materials, but not for the VOA unit that we use as a normal tool. In your case, the current is too small that we never sense it a bit.
  5. May 14, 2007 #4


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    I'll bet that anyone who has ever used a multimeter at all has tried this. I've certainly never experienced anything like what you describe. As a strange coincidence, though, I've had exactly that reaction after W insisted upon testing my blood-sugar a couple of weeks ago. She poked me about half a dozen times before finding any. The tip of my ring finger has been numb ever since, and I suspect that she damaged a nerve with the lancet. Given the shape of a multimeter electrode, is it possible that you were squeezing it hard enough to compress a nerve in your finger? If so, the feeling should return in a reasonable amount of time.
  6. May 14, 2007 #5
    Thanks for your answers.

    No, that didn't happen. I was just holding the electrodes, without pressing at them at all.

    I am not really worried although it still feels a bit weird (ok, maybe it's just my idea). I understand that the current in such cases is just too small to cause anything, but I wanted to know how much is actually. I assume that it must be ~1-100μA or something like that.

    Does anyone know what current can actually cause damage? Of course, anything >1A is obviousy very dangerous but what about mA's.

    Thanks again
    Last edited: May 14, 2007
  7. May 16, 2007 #6
    As little as 250 mA can disrupt your heart beat and kill you.
  8. May 16, 2007 #7
    Emicro, but that's straight to your heart not to your limbs, which have a very large resistance, thus protecting your heart.
  9. May 16, 2007 #8
    abdo375 if you have 250 mA of current through a 5 Mega ohm resistor or 250mA through a 1 ohm resistor, which one has more current going through it?
  10. May 16, 2007 #9
    Isn't it neither, but the one going through the larger resistor is from a higher voltage source and thus more likely to sustain a high power/energy discharge thus making it potentially more dangerous?
  11. May 16, 2007 #10
    You are correct on both points. My point was that 250 mA is 250 mA no matter what resistance it goes through.
  12. May 17, 2007 #11
    I checked 2 multimeters that work with 2x1,5V batteries, and the maximum voltage (I measured it with another multimeter) that they produce when measuring big resistances is 2.9-3 V, as one would expect. So, normally they can do no harm to a human, as our body resistance is much more than 12 Ohms (3/12=250mA)- i am just referring to 250mA because Emicro brought this up.

    Anyway, I think that the current caused my hand's muscles to contract (is it called so?) because the feeling i still have is that my hand is a bit tired. I am still confused though, why such small current would cause anything to my body.

    Also, I am still not sure if I read 0.85 KOhm or 0.85 MOhm when I measured it, but in either case the current is 3.5 mA maximum, which I think is not dangerous

    One thing is for sure, I am not measuring again my body resistance...
    Last edited: May 17, 2007
  13. May 18, 2007 #12
    Does your meter have a diode test function? My Fluke 87V does, and it supplies around 7 volts. I put its two leads on my tongue and I actually felt it, where on its resistance setting I feel nothing.
  14. May 18, 2007 #13
    It wasn't my meter so I am not sure, but I don't think that it had diode test function. Also, I had set it to measure resistance, and as I told you, I afterwards measured its voltage in that setting with another multimeter, and it was 2.92V, plus it works with 2x1.5V batteries so it can't actually supply more than 3V. Most people probably don't feel 3V, but I did :frown:
  15. May 18, 2007 #14


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    Your reaction is not due to the meter, perhaps it is psychosomatic since you seem to want it to have done some harm.

    The Navy taught us that as little as 50ma thru the heart could cause troubles, I have seen other sources that said 20ma and different ones that said 100ma. The fact is that a low voltage applied to the skin will not induce any current thru the heart. Now if you were to stab a lead under the skin in each arm you may be able to induce harmful currents thru the heart (I said MAY, damn it, so don't quibble with me) :devil:
  16. May 18, 2007 #15
    I have been stung by electricity many times, I have even been hit by 3 kV and have never had any lasting effects. I think that Integral is correct in his assumption that what ever hurt you, it wasn't your meter.
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