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Maximum safe level of Electrical Voltage

  1. Nov 2, 2004 #1
    I have one Question to trouble u

    What level of electrical voltage would normally be considered safe ?
    [100 Words]
     
  2. jcsd
  3. Nov 2, 2004 #2

    Cliff_J

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    50VDC and do your own homework to find the AC equivalent. (11 words)
     
  4. Nov 2, 2004 #3
    It's current that kills, voltage will just piss you off.
    10 words
     
  5. Nov 2, 2004 #4

    Cliff_J

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    Seventy billion picoamps is small current. (6 words, beat that!! :smile:)

    ArFat - if the sarcasm isn't obvious, this is a homework question and no one will provide you with an answer that you should look up and understand.
     
  6. Nov 26, 2004 #5
  7. Nov 26, 2004 #6

    Astronuc

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    Staff: Mentor

    Depends on the current. (4 words).

    At zero current, even a high voltage can be safe (static electricity). This implies one is well insulated.

    Actually, HV (e.g. 300+ kV) lines (one phase at a time) can be serviced by helicopter. The lineman wears a conductive suit (like being inside a Faraday cage), grounds the line to the helicopter and can work on line while it is energized. It's safe as long as one knows what one is doing.

    Putting 12V directly across the heart could probably be fatal. I received a nice little zap one time when hot and sweaty, leaning across an HO model railroad track with only 12V between the conductors.

    Also from personal experience, 120 V can be quite uncomfortable, but 440 V feels like getting hit by a truck.
     
  8. Nov 26, 2004 #7

    chroot

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    The original poster was probably asking about the voltage that can be applied to dry skin without causing any effect at all -- not even sensation. That voltage is generally accepted to be within 40 to 50 volts.

    - Warren
     
  9. Nov 28, 2004 #8
    I survived 1.2MV

    [3 words?]
     
  10. Dec 5, 2004 #9
    yeah it would take a looooooot of volts to kill someone. my physics teacher once told us about how in university him and his friend were messing around with a tesla coil (i think that was it..) and accidentally flipped it on and shocked his buddy with about 50+ kv. and im pretty sure the guy was knocked out pretty bad, but he survived alright.
     
  11. Dec 5, 2004 #10
    Tesla coils are a different sort of animal when it comes to getting shocks. A properly built tesla coil has only high frequency output. It will only travel over your skin. It does not really penetrate.
     
  12. Dec 6, 2004 #11
    No, voltage of any magnitude never did anything to anybody. It's the current. Did you know that the potential gradient of the atmosphere is such that on an average day, the air around your head has a voltage of about 500 V with respect to your feet?
     
  13. Jan 9, 2005 #12
    If the resistance in your body changed without the effect of a change in voltage then you could only focus on the current- wattage. Theoretically 20,000 watts of power at 2 volts will not overcome the resistance of a persons body. The other factor is where you are placing the voltage.A 9 volt battery on the tongue can easily be interpreted as overcoming the resistance with in your saliva but there is not enough induced force to do serious damage. The resistance in your body sets up a situation where only X amount of wattage can ever be consumed per unit of time. The fact of the matter is, when you over come the resistance in your body with enough voltage, the heat that results is what damages the body given a sustained wattage to uphold the voltage. -random fact- an electric chair is raised to 2000 volts to overcome the resistance of the body easily, moments later the voltage is dropped to 1000volts cooking a person from the inside out :yuck: . The induced force can be measured as wattage. Amps are amps no matter what situation they are placed under. Amps are a measurement of total potential of the total electric energy; where the amp can be transformed into any voltage with a given amount of potential(wattage) energy. Time duration of the system is the inverse resultant of wattage consumption per unit of time (*times*) the inverse total wattage potential in the system.

    WATTS consumed 1 1
    _______________ X __________ = _______
    unit of time Potential amount of watts Delta (T)


    edit: sorry the equation didn't show up quite right..... i hope you get the idea
     
    Last edited: Jan 9, 2005
  14. Jan 9, 2005 #13
    only current(also duration) will hurt you not voltage. this table gives you an idea!

    current range response

    0.5 to 3 mA Feel the energy, tingling sensation
    3 to 10 mA Experience pain, muscle contraction
    10 - 40 mA Brain says let go; but physically cannot do so(Grip paralysis)
    30 - 75 mA Respiratory systems shuts down
    100 - 200 mA Experience heart fibrillation
    200 - 500mA Heart clamps tight
    Over 1,500 mA Tissue and organs burn

    D.Srinivasa Rao,
    Engineer(E)
    Loktak Power Station,
    Loktak-795124
    Manipur,
    INDIA
     
  15. Jan 9, 2005 #14

    GENIERE

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    Presumably the tables indicate externally applied voltages. With electrodes in direct contact with the heart, only a few micro amps can cause fibrillation. If I recall, only several volts applied is needed to obtain a few micro amps.

    ...
     
  16. Jan 27, 2005 #15
    Time,Duration,and Path are the determining factors. More people are damaged?injured? killed! by 120v 15a than any other combination's of Volts and Amps.
     
  17. Jan 27, 2005 #16
    I think what you mean is just plain 120 volts. By saying 15 amps I think you mean coming in contact with a circuit that is capable of delivering UP TO 15 amps. It is extremely unlikely anyone who comes in contact with a 120 volt wire fused at 15 amps actually will carry the full 15 amps. They would be dissipating about 1800 watts in/on their body by doing so.

    I will agree with you though that 120 volts household current is probably the most overlooked under-respected of all. I can tell you that standing on a dry wood floor on a construction site in direct contact with 120 volts and I feel absolutely nothing. That sort of thing can make a person complacent. Then you get careless and come in contact with that same voltage on a wet concrete floor with wet shoes. Bad news. When working with it the best thing to do is always in the back of your mind be thinking that it is possible the current COULD POSSIBLY BE ON! You then tend to watch your footing more and tend to keep your feet dry and keep yourself in a position where coming into contact with a live wire will do you minimal harm. Dry skin is an electricians best friend.
     
  18. Jan 29, 2005 #17
    Dry skin

    you are correct, dry skin is the Electricians buddy, and the chances of taking on the full 1800 W load is unlikely at 120v. What about 277v or worse yet 480v? I know from experience that 277v will grab you (or rather you will grab it) and the only way I got loose was by falling off a ladder. The involuntary response of muscle contraction took over,and although I was only on for a few seconds I could not make my hand let go. I know of a couple of guy's missing parts of fingers by getting in between ground and 480v. A pleasure I would rather not have.
     
  19. Feb 3, 2005 #18
    Haha, not need to debate so long about it.

    Do a live experiment with a signal generator on a human being, then we will know the facts!
     
  20. Feb 3, 2005 #19
    Sure. You can be the human subject.

    Actually if you paid attention I already did this experiment. Or at least part of it. As I previously posted I said I can stand on a dry wood floor in direct contact with a 120 V wire and not feel a thing.
     
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