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Thread: Mechanism of electrical shock

  1. #1 Mechanism of electrical shock 
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    While reading the post about the danger of AC vs DC electrical shock, I realized that I don't fully understand the mechanism of electrical shock.

    I can understand it fully when the body closes a circuit. For example if I have two wires sticking out of a household outlet and I grab them each with one hand then my body closes the circuit and a current would surge through my body, coming in one hand and out the other. The current would naturally burn me.

    But what if I just grabbed onto one wire? Would I get shocked as well, and if so why and under what circumstances?

    Also how does one get electrocuted via the infamous "hairdryer in the bathtub"?

    And why is standing under a tree in a thunderstorm dangerous? If the lightning strikes the tree, how does that affect those standing under it?


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  3. #2  
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    If you are only touching one wire, you won't get shocked. A bird can land on a high voltage wire and nothing happens. If you are touching a hot and a neutral, you will complete a circuit and get shocked. If you are touching a hot wire and a ground, and if the neutral is grounded, you will complete a circuit and get shocked. This is likely to happen if you are outdoors standing on wet ground, and your electric saw or drill has a short to the metal case. Or if you are in the bathroom or kitchen and you are touching a grounded water pipe, that will complete a circuit to the grounded neutral side of the circuit.

    The hair dryer or radio will not hurt you if it just falls into the water with you. If you touched it though, the circuit could be completed through you and a grounded drain or water pipe.

    When the lightning strikes a tree near you, it creates a path of ionized air the lightning follows from the cloud to the tree. Once it hits the tree it can jump from the tree over to a nearby object like you.


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  4. #3 Re: Mechanism of electrical shock 
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    Quote Originally Posted by ScienceWizard
    While reading the post about the danger of AC vs DC electrical shock, I realized that I don't fully understand the mechanism of electrical shock.
    THe nervous system works by passing minute chemically generated electrical pulses around the body. To move a muscle, a tiny electrochemical signal is sent to the muscle. When you experience an electric shock you are effectively sending massive signals many thousands of times stronger than natural signals. It's a bit like somebody whispering to you from across a room when all of a sudden a fog horn is set off, you now respond to the horn and not the whisper.

    But what if I just grabbed onto one wire? Would I get shocked as well, and if so why and under what circumstances?
    It is possible to get a shock from a single wire, you do not need to complete a circuit to receive a shock. You merely need to exchange (one way or the other) electrons with an object which is at a different potential (voltage) than you.

    Also the term 'wire' is very misleading, any material with the ability to contain 'free electrons' can cause a shock (wet paper for example).


    Also how does one get electrocuted via the infamous "hairdryer in the bathtub"?
    Unless the bathwater is is pure it will have the ability to allow current to flow through it, if the hairdryer is connected properly then most probably the majority of any current would flow between it's own conductors within the unit (this is the shortest path and in a uniform medium the path of least resistance).

    And why is standing under a tree in a thunderstorm dangerous? If the lightning strikes the tree, how does that affect those standing under it?
    Mostly in a thunderstorm (which usually have short yet violent bursts of rain) the tree trunk will be dry (sheltered by it's canopy) you however may be soaking wet, electricity will take the path of least resistance - you! However it is not always that simple.

    If you and I are both struck by lightning, each dressed alike, my overcoat is saturated yours is dry. My under clothes are dry as are yours(at least to start with :wink: ). I will have a higher chance of survival than you as the lightning will mostly travel through my wet outer garments. In your case the wet part is the inside of your body....

    Every case is different, In a car the lightning will travel around you through the chassis (as also in a plane) see this youtube video.


    http://www.youtube.com/watch?v=8o2oachaHXY
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  5. #4 Re: Mechanism of electrical shock 
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    But what if I just grabbed onto one wire? Would I get shocked as well, and if so why and under what circumstances?
    It depends on the voltage(AC orDC) and the amperage behind it. People touch the hot battery cable of thier car all the time with no problem but I have a friend that has lost the use of his left arm from 240vDC,200A shock.

    Also the resistance of you body plays a part in the severity of the shock,it's Ohm's Law I=E/R. The amount of current necessary to kill a person is small,therefore, it is easy to exceed lethal levels of current flow, especially if the skin is broken, wet, or damp with sweat.

    Also how does one get electrocuted via the infamous "hairdryer in the bathtub"?
    The power supply cord used on most modern electronic/electrical equipment has a three prong plug.The power distribution system used in the United States is 120VAC, the "hot" wire(black) is the 120 volts and the other wire(white) is the neutral or ground(three wire system).

    If a person were to touch the neutral wire only, no shock would result, simply because there is no voltage on it. If he were to touch the hot wire only, again nothing would happen to you unless some other part of your body were to become grounded.

    The entire purpose of the three wire system is to provide a separate ground path which will eliminate any possibility of shock. If your home was built in the last 20 or so years you have or should have whats called a GFI in key places of you home.

    http://hyperphysics.phy-astr.gsu.edu...ctric/gfi.html


    And why is standing under a tree in a thunderstorm dangerous? If the lightning strikes the tree, how does that affect those standing under it?
    Voltage can and do jump when it's high enough,it jumps 1 inch for every 5kv. if you are outside and wet you are well grounded. water is a very good conductor.When I worked at this one paper mill they had a 13.8v Dist. systems and we always had to wear arc flash gear when we were in the area of this system because of the fact that an arc could jump.
    Thirst is a ďstrongerĒ need than hunger. Likewise, if you are very very thirsty, but someone has put a choke hold on you and you canít breath, which is more important? The need to breathe, of course. On the other hand, sex is less powerful than any of these. Letís face it, you wonít die if you donít get it!.....Maslow
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