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Ac or dc

  1. May 5, 2010 #1
    Which is most dangerous for human being 230 V ac or 230 V dc voltae supply
     
  2. jcsd
  3. May 5, 2010 #2
    Depends on the current passing through your body.
     
  4. May 5, 2010 #3

    Please elaborate
     
  5. May 5, 2010 #4
    Last edited by a moderator: Apr 25, 2017
  6. May 11, 2010 #5
    All elevators are required to be constructed, installed, and maintained in accordance with ANSI/ ASME A17.1. Reference standards include NFPA 70 (NEC) for the electrical equipment wiring and
    NFPA 101 (Life Safety Code), Chapter 6, Features of Fire Protection, and Chapter 7, Building Service and Fire Protection Equipment.
    There shall be a 300-V limitation on all operating control and signal circuits and related equipment, including door operators. Exceptions are permitted for 25 to 60 Hz ac if the current cannot under any conditions exceed 8 mA, or for dc voltage if the current cannot, under any circumstances, exceed 30 mA.
    For example, 1/10 of an ampere (amp) of electricity going through the body for just 2 seconds is enough to cause death. The amount of internal current a person can withstand and still be able to control the muscles of the arm and hand can be less than 10 milliamperes (milliamps or mA). Currents above 10 mA can paralyze or “freeze” muscles. When this “freezing” happens, a person is no longer able to release a tool, wire, or other object. In fact, the electrified object may be held even more tightly, resulting in longer exposure to the shocking current. For this reason, handheld tools that give a shock can be very dangerous. If you can’t let go of the tool, current continues through your body for a longer time, which can lead to respiratory paralysis (the muscles that control breathing cannot move). You stop breathing for a period of time. People have stopped breathing when shocked with currents from voltages as low as 49 volts. Usually, it takes about 30 mA of current to cause respiratory paralysis. Currents greater than 75 mA cause ventricular fibrillation (very rapid, ineffective heartbeat). This condition will cause death within a few minutes unless a special device called a defibrillator is used to save the victim. Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.
    The amount of current passing through the body also affects the severity of an electrical shock. Greater voltages produce greater currents. So, there is greater danger from higher voltages. Resistance hinders current. The lower the resistance (or impedance in
    AC circuits), the greater the current will be. Dry skin may have a resistance of 100,000 ohms or more. Wet skin may have a resistance of only 1,000 ohms. Wet working conditions or broken skin will drastically reduce resistance. The low resistance of wet skin allows current to pass into the body more easily and give a greater shock. When more force is applied to the contact point or when the contact area is larger, the resistance is lower, causing stronger shocks.
    The path of the electrical current through the body affects the severity of the shock. Currents through the heart or nervous system are most dangerous. If you contact a live wire with your head, your nervous system will be damaged. Contacting a live electrical part with one hand—while you are grounded at the other side of your body will cause electrical current to pass across your chest, possibly injuring your heart and lungs.


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    Creative thinking is enjoyable, Then think about your surrounding things and other thought products. http://electrical-riddles.com
     
  7. May 31, 2010 #6
    Could anyone please confirm me that which of AC or DC current holds the body and which of it throws off when it is touched on and why!!
     
  8. May 31, 2010 #7
    Around the turn of the century (1899-1900), Edison and Tesla debated about whether ac or dc was safer, and which was better for electrocutions. Dogs, horses, and even an elephant were electrocuted in public as demonstrations of the lethality of electric shock. Google " AC DC Edison Tesla Westinghouse electrocution"

    Bob S
     
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