AC or DC- Which one is more dangerous

Discussion in 'General Electronics Chat' started by aamirali, Feb 28, 2012.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
    415
    1
    1. 220V ac or 220V dc, which one is more dangerous. I think in ac peak voltage can go upto 220*1.414 ac. So ac is more fatal. Right?

    2. At what voltage human body starts feeling shock?
     
  2. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    DC tends to be more dangerous because it causes more complete paralysis thus preventing the victim from letting go--the zero crossing of AC tends to somewhat help the victim to let go.

    Regarding shock and voltage, it is not exactly a voltage issue as the variable of skin resistance plays an important part--it depends upon how much current is flowing--5mA is quite noticeable, but not considered life threatening.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    Don't forget its really the current that kills not the voltage level.
    1000VAC @ 5mA is a good tickle.
    100VAC @150mA is lethal.

    The neat thing is that there are studies that over 200mA will not kill you because the heart will clamp shut protecting the body from death.. But serious burns,etc.. will/can occur.
     
  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    That sounds bogus to me. Someone might be lucky every now and then and have that happen, but in most cases, the victim will be killed instantly (especially if it's across the heart! :eek: ). My two cents worth.
     
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    It's somewhat true. The concept is the same as "cardioversion" http://en.wikipedia.org/wiki/Cardioversion, with a defibrillator. For an erratically beating heart, the shock stops the heart briefly and allows the normal timing mechanism within the nerves to take over. It depends on precise timing of the pulse. Inadvertent electrical shock could do that :) ....or just stop the heart beating permanently. :(
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    I'm with you on the sounds bogus but I've seen/heard of many instances (lightning strikes/direct pole mounted transformer shocks,etc..) all where the individual was not killed.

    The thoughts are that the chest muscles clamp the heart stopping the heart completely and preventing ventricular fibrillation which is what typically kills shock victims. Those thoughts are everywhere (even Wikipedia..The source of all true information :) )
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    That works with DC (or a DC pulse), but AC can cause the heart to fibrillate and stop beating effectively. That's why, in general AC is more dangerous than DC.

    Also you can't necessarily let go if you have grabbed a conductor that is giving you a strong AC shock. The zero crossing of the AC is too short for the muscles to have time to relax. Many years ago my cousin grabbed their refrigerator handle and (due to a short) received such a strong AC shock that she couldn't let go. Her mother noticed what was happening and had to pull her away from the handle.
     
  8. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    The occurrence of ventricular fibrillation cannot be easily predicted as it depends upon many variables including current level, current path(s), victim sensitivity, period of discharge, perhaps polarity, AC or DC--complex indeed!
     
  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Very complex indeed...and it's hard to find people willing to act as the experimental and control groups. ;)

    Ken
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    I was in a situation once where an old school metal case AC powered hand drill shorted the line to case when the button was pressed. Of course the drill was firmly in my hand when this occurred. Rather then leaving me a way to let go it instead twisted my arm in towards my body and I had no muscular control.

    Had the bit not wrapped up in my shirt stalling the motor and tripping the breaker I would not be telling you this story.

    Moral: They are both equally dangerous and should always be approached with caution and protection.
     
  11. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    Interesting question, and not a new one.

    The relative danger of AC versus DC was part of the war between Edison and Westinghouse over a hundred years ago, where Edison supposedly electrocuted some horses and elephants to demonstrate the danger of AC -

    http://en.wikipedia.org/wiki/War_of_Currents

    But I think the question is kind of bogus. It's like asking whether a shotgun is more dangerous than a rifle, when in fact, they both are dangerous enough to kill you.
     
    vpoko likes this.
  12. #12

    Expert

    Nov 30, 2010
    16,278
    6,790
    This subject has been rehashed so many times on this site that I don't see a need to go through this again. It seems that every possible opinion can be found in a group of a hundred people, even smart people that know a bit about electricity, but the only one that matters to me is, "Don't touch the electricity". Whether it kills you or not, it hurts. Just say, "no" to getting an electrical shock.
     
  13. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    I was about to bring that up. You have some mistakes though--don't trust Wikipedia. The "Battle of the Currents" was NOT between Edison and Westinghouse. It was between Edison and Tesla. (As you can see by my profile picture, I'm a huge fan of Tesla, and it really bugs me that he's been forgotten by most people and history books--he's really the father of electricity as we know it today). Westinghouse owned a big company that just sat in the background as Edison claimed DC was safer, and Tesla assured everyone that AC was safer. To put it simply, Westinghouse was just waiting for the winner to emerge, and then he would fund their experimentation and production. Tesla is really who was important in all this. Edison electrocuted elephants with AC to show how "dangerous" it was, but he did not show what DC did. He even paid some kids to go through the neighborhood and steal peoples' cats and dogs from their yard, and he electrocuted them in public to show the dangers. Tesla, on the other hand, demonstrated the effects of AC on himself--successfully, without injury. Also, DC caused excessive heating of the conductors, which led to hundreds of house fires during its time. I honestly believe that AC is MUCH safer than DC, if only for the heating reasons. Electrocution is not the only danger when it comes to electricity.

    Completely agreed. However, as I mentioned in my response to davebee, electrocution is not the only hazard.

    Regards
     
  14. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Now for my horror story--never told it before.
    When I was a teen some 50 years ago, I constructed a fabulous 1000V 2A DC power supply using old plate supply transformers and a 5A Variac. Learned much and about safety too.

    Do not remember the voltage setting, but I got across it somehow--hand to hand--had not learned the single hand technique at that point. Unable to let go, I just sat soaking it up until I fell off the shop stool at which point the short banana leads pulled out--whew, what a ride!
     
  15. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    Yikes, that's intense. You're very lucky to be alive! That voltage is more than enough to bring the current deep into body tissue. I'm glad to have you here!

    I just remembered another thing about AC vs DC that is really important. DC has the ability to flow deep into body tissue, causing severe nerve and muscle damage. AC has a little bit to its advantage--the "skin effect". The higher the frrequency, the less deep the current is able to penetrate into tissue. 50/60 hz is still very dangerous, but it cannot penetrate as deep as DC.
     
Loading...