Challenging question about electrocution

Discussion in 'General Electronics Chat' started by Thanks4helpin, Jun 23, 2015.

  1. Thanks4helpin

    Thread Starter New Member

    Mar 14, 2012
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    Hi All,

    Wanted to thank you in advance for helping me with this question. And please, no jokes about Darwin Awards - I really want to know to satisfy my insatiable curiosity and would really appreciate if you can assist :)

    Please see diagram, I have labeled parts A (first prong) , B (2nd prong), and C (end which plugs into device)

    Scenerio 1) Pretend this is a USB plug, with the end attaching into an ipod or iphone to charge. what happens if a person touches A and B with one hand, and then C (end) with another hand? If it is a USB plug, will it do nothing because the charge is too low? person is standing on carpet. Will the person get a shock, or is the charge too low.

    Scenerio 2) Same as scenerio 1, but person touches A, B and C with one hand?

    Scenerio 3) Pretend this is not a USB plug, that the end "C" is a small metal end. If the person touches A and B with one hand, and then C (end with another hand), again standing on carpet, will the person be shocked? to cause bodily harm? Or will the carpet protect the person

    Scenerio 4) Same as Scenerio 2 but person touches A,B, and C with one hand?

    Thank you so much again :) Have a great day


    In response to answers below: Thanks so much everyone. Yes I'm not familiar with electrical terms so forgive any wrong uses of my language. It seems that everyone is talking about the electrical current between A and B, not A and B and C? So C doesn't come into the equation at all even in Scenerio 3? I know that A and B together will give a shock, but I was curious about the A + B + C effect, if it would complete a circuit (since when you plug C into a device, it is charging the device, so the circuit is going to C, I thought..) Yes this is assuming it is a USA plug of 120 volts.
     
    Last edited: Jun 23, 2015
  2. mxg2579

    New Member

    Jun 10, 2015
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    Are you saying that the plug is plugged into the wall? Because if you touch A and B and it is plugged in, you are touching 120 Volts AC (in US) and you will definitely feel a kick.
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    I couldn't help wondering if there's anything in the forum rules about aiding and abetting a dumbass?!!!
     
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  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Whatever is contacting points A and B and whatever part of the body is between them will get a shock. Depending on skin thickness and moisture levels the shock may be anywhere from mild to deadly.

    Point C is electrically isolated inside the USB adapter so it has no direct electrical connection to points A or B.

    As for the floor realistically if the floor is anything but wet concrete or steel the odds of being able to make a solid enough electrical connection between either points A or B and the floor are very low. Dry carpet, wood, socks, footwear, tile, and even dry concrete are all typically pretty good insulators at normal household voltages.
     
  5. BReeves

    Member

    Nov 24, 2012
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    If "Plug" is a transformer, "B" will more than likely be low voltage and you will not feel it.
    If you touch "A" and "B" you could get killed.
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
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    Drawing & verbage do not seem to match. Assume USB plug, output might be 5 V = no shock. If it is truly a wall outlet then output is 120, 60 HZ or around 220, 50 Hz, either can give lethal shock depending on how good the hand-metal connection is. Carpet does no enter the testing.
     
  7. #12

    Expert

    Nov 30, 2010
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    Only the part about giving advice that can get somebody hurt. Asking beginner level questions is a tradition here. ;)
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    If you look at it in the context of the post I was replying to, it makes more sense.

    Having another look at the TS OP, it could be a case of English as a second (or third) language.
     
  9. #12

    Expert

    Nov 30, 2010
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    Oh well. Confusion happens. :p
    No big deal.
     
  10. ian field

    Distinguished Member

    Oct 27, 2012
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    At first reading - the OP reminded me of when I worked for a firm that made faradic muscle exercisers, the portable model with shoulder strap ran off half dozen C cells, but had a power jack for a wall wart. It was more than just the once we got a return from someone who'd cut the lead off the wall wart and fixed it into a 3 pin plug. The very early model had a 2SB77 or similar in the CR delayed bias blocking oscillator, usually the can would be blown off the TO1 transistor and rattling about in the case. There would invariably be a few vapourised PCB tracks - the TO1 header was usually still there, looking rather funny with the stumps that the crystal used to be attached to.

    Since the original was based on old PNP germanium transistors, when I updated the design, I minimised reworking of old stock by adopting the PNP ZTX751 - those just disappeared when people plugged them into the mains.
     
  11. #12

    Expert

    Nov 30, 2010
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    Interesting anecdote. I never suspected that some people that would cut a wall wart out of a cable and attach the cable directly to the receptical. This seems to indicate that some of the truly stupid warnings posted on retail products has a valid audience.
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    Apparently most restaurants etc give "CAUTION _ HOT LIQUID" warnings on hot drinks they serve.

    Warnings of this type are often printed on the packaging of microwave ready meals.

    The instructions for the muscle exerciser give a very clear warning on page 1 not to switch it on while holding a pad in each hand - some woman opened the box and did exactly that first.

    We got a visit from trading standards within days - the unit produces 200V pulses, but very narrow needle pulses, so the energy is very low. This was demonstrated to the trading standards officer's satisfaction by loading a unit with an inverse parallel pair of LEDs and showing how dimly they lit.

    A significant segment of the customer base was body beautiful 'men'. They were the worst offenders for trying to boost the output to that extreme.
     
  13. mxg2579

    New Member

    Jun 10, 2015
    15
    7
    So are you saying I did something wrong? Because I surely was not aiding him any means. Trying to clarify his question is more like it. Was it a "beginners question"? Sure. But trying to clarify what he's asking isn't a bad thing I don't find.

    And what exactly do you mean by English as a second language? Are you saying for the OP, or me?

    I am not being confrontational, I really am just asking.
     
    Last edited: Jun 23, 2015
  14. Thanks4helpin

    Thread Starter New Member

    Mar 14, 2012
    19
    0
    Thanks so much everyone. Yes I'm not familiar with electrical terms so forgive any wrong uses of my language. It seems that everyone is talking about the electrical current between A and B, not A and B and C? So C doesn't come into the equation at all even in Scenerio 3? I know that A and B together will give a shock, but I was curious about the A + B + C effect, if it would complete a circuit (since when you plug C into a device, it is charging the device, so the circuit is going to C, I thought..) Yes this is assuming it is a USA plug of 120 volts.
     
  15. WBahn

    Moderator

    Mar 31, 2012
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    Assuming that A and B are the line and neutral prongs of the plug, as soon as you touch both A and B with one hand you will get zapped. C doesn't enter into it.

    If you hold onto just A (the line prong) then you might get zapped then and there depending on whether there is a path to ground through any other part of your body. Assuming their isn't, the to get zapped you need to provide such a path. The C end of your cable may or may not, then depends on how it is wired. You mentioned a USB cable but a USB cable has four conductors plus the shield. Which one are you talking about? If you are talking about the shield, then that may well be floating for a wall charger so that the device being connected to can dictate the choice of reference for the shield.
     
  16. Thanks4helpin

    Thread Starter New Member

    Mar 14, 2012
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    hi WBahn thanks for your helpful reply. Not really sure what you meant by the last sentence but what I mean is a C end of the cable where it is not a USB, just a normal metal piece. Doesn't even need to plug into anything, more like an extension cord, but having a metal piece at the end. Will that make a difference? or because the person is standing on carpet there is no path to ground anyways?
     
  17. WBahn

    Moderator

    Mar 31, 2012
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    What is this metal piece connected to? That makes ALL the difference!
     
  18. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Or, perhaps, member assisted suicide?;)

    Oh yes! Many a device has been dispatched to the hereafter (occasionally in the company of its user) following replacement of "that unsightly, cumbersome, oversized plug"...:rolleyes:

    TTFN
    HP
     
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  19. #12

    Expert

    Nov 30, 2010
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    LOL!!! Is that what they mistake it for?!!!
    Never wooda guessed! :p
     
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  20. ian field

    Distinguished Member

    Oct 27, 2012
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    If you're talking about the leads coming from manufactured items like wall warts, chargers etc - they should be safe under any normal use.

    They should either be double insulated or any accessible electrical contact must have some point returned to safety earth.

    A typical example of double insulated on a wall wart with iron cored type transformer; both the primary and secondary winding have their own completely separate bobbin, usually the primary also has a clip on plastic shield, so in catastrophic failure, blown away strands on the primary bobbin can't droop down and touch the secondary.

    However - that's not to say some imports aren't a bit dodgy!
     
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