Electrioution

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  #1  
Old 11-23-04, 09:08 PM
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Electrocution

Hello-

I have a question about how one becomes "electrocuted." I was watching a Mythbusters episode on TV and I'm a little confused.

And let me say in advance that I would NEVER EVER do any of the below things, I am simply asking from a theoretical standpoint.

So lets say someone opens the electrical box in their house, and exposes the two wires that come into the top of the box from the utilities. If a very stupid person touches only the "hot" lead, do they become electrocuted? What if this person is standing on a very thick rubber mat? In the rubber mat example, if the electricity can't make it to "ground" through the rubber mat, does that mean the electricity doesn't flow through one's body and therefore the person won't be electrocuted?
 

Last edited by ualdriver; 11-23-04 at 09:45 PM.
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  #2  
Old 11-24-04, 04:51 AM
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Electricity needs a path back to the source. It does not need a path to ground. Simply touching a hot wire won't hurt you. The current has to pass through your body and exit. Depending upon what it passes through and how much current there is, you will feel the shock and quite possibly suffer from it's efffects. And the effects can be short term or long term, immediate or delayed.

Your heart stopping or going into fibrillation would be a short term immediate effect. And not a good one either.

Damage to your other body muscles would be more long term. But still not good.

The idea of a return path is why they teach electricians to use one hand when working in a panel if at all possible.
 
  #3  
Old 11-24-04, 10:19 AM
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So basically, when one opens their electrical box, as long as they are wearing sneakers or standing on a rubber mat, they would feel nothing if they accidentally touched the hot bar or wire, assuming their other hand or other body part wasn't touching a neutral or ground?

I have another question then. Let's say that this hypothetical person has an open electrical box and touches the hot wire while standing on a thick rubber mat and is not touching anything else. He's completely insulated except where he is touching the box. Where does the electricity go? Is the electrical flow now in this person's body with basically nowhere to go and the person doesn't even feel it? Or does the electricity never even enter his body because it has nowhere to go if it did?

I don't know if you're familiar with the show Mythbusters on the Discovery Channel, but they did a show where they dropped various electrical appliances in a bathtub while they had a dummy rigged with an ammeter and a voltmeter and they wanted to see that if the GCFI failed stop electrical flow (faulty GCFI) would the person be electrocuted? But I would think that since your fiberglass bathtub is probably not electrically grounded (assuming the fiberglass tub insulates your copper plumbing leading to the bathtub), that if the appliance fell in you wouldn't be electrocuted because there is no place for the electricity to go, hence no electrical flow? In their experiment, they purposely "grounded" the tub, which I thought would be unrealistic.
 
  #4  
Old 11-24-04, 10:30 AM
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Hah, unrealistic? Go down to your basement and look at the water line comming in, it is grounded. Many old plumbing fixtures are ran with cast iron pipes. If your water was running it is grounded. It isnt' unrelasitic at all. You probably want to post any of your mythbuster complaints to their website. Some of their tests are kind of crappy. But I still like the show
 
  #5  
Old 11-24-04, 10:59 AM
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Electricity needs a path back to the electrical utility's transformer, where your juice comes from. That's true. BUT, it is happy to travel to the Earth, also. If you are standing in a puddle of water barefoot in your basement and touch one bare hot wire or bus you will definitely get juiced!

If in your example, your basement's dry and you're standing on a thick rubber mat and touch one bare hot wire or bus, you will most likely NOT get juiced. (But why on earth would anybody want to do this???)

If you are upstairs, with wooden floors or carpet, standing there in your socks and touch a live hot wire you will PROBABLY not get juiced. That's because carpets and wood are very poor conductors. Very poor conductors are usually called insulation. If you are standing on a heat register in your socks or bare feet, though, and you touch a bare hot wire, chances are you'll get juiced because your heating system is usually pretty well grounded and all the ductwork to and from it is usually metal. This would be a good path to ground.

Now, to help clarify your other question. Most materials (including human body parts) are conductors. They transfer electrons. Humans, though, are not very good conductors. Example: Say you pull a receptacle out of its box, remove the hot (black) and neutral (white) wires. Keep them separate from one another. Now DO NOT TRY THIS AT HOME: Let's say you nuts. But not suicidal. So you would place one hand in your back pocket. Now, with just the other hand, let's say you accidentally touch the hot with your thumb and the neutral with your forefinger simultaneously. ZZZZZZZIIIIIIIIIIIINNNNNNNNGGGGGGG!!! And you would quickly pull your hand back. You will notice, though, that there was no flash, no explosion, no smoke, and the circuit breaker did not pop. And you're still alive, no less. This is because humans are poor conductors. Very little amperage was able to flow through you instantaneously before you knew you hated that feeling and pulled your hand away. Now, if instead you touched the black and white wires themselves directly together you would see a big flash of light, hear a loud POP, and the breaker would trip. That is because copper is a very very good conductor and many amps were able to flow between the two wires instantaneously.

One variable: the higher the voltage, the better able we humans are to conduct electricity. So stay off utility poles if you know what's good for you.

Now, to answer another of your questions. If you are not connected to anything electrically, like standing on a thick rubber mat, and you touch one hot wire, the electricity doesn't enter your body in the first place. Think of it like a bridge out. Juice has to have someplace to go. If it does not have a path to neutral or a path to ground, it doesn't "go" anywhere.

Think of a light bulb. You have one hot wire connected to the light fixture, and one neutral. The bulb is lit. The electricity is flowing through the filament, producing heat and light. The hot is coming from the utility's transformer on the hot wire, traveling through the filament and returning to the transformer on the neutral. If you lift the neutral wire off the fixture, the light bulb goes off, because the juice has no path it can't flow. Same with you. Take away the neutral, or a path to ground, and juice will not flow through you.

But all you folks out there - just trust these theories and explanations and do not try to see for yourself or prove any of them!!!

I hope that helps. If not, it was fun to write about, anyway.

JuiceHead
 
  #6  
Old 11-24-04, 11:07 AM
SkyKing
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Shouldn't be on utility poles? Oh man, what have I been doing for the past 4 years! I quit! :-)

All kidding aside, you are right, they are no fun to be near, especially in bad weather. I don't like being closer than 2 ft to any power line or transformer, unfourtunately, in the cable/phone/power industry you do not have that luxury.
 
  #7  
Old 11-24-04, 11:35 AM
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Utility poles: Trained professionals only. Definitely no drugs or alcohol, though. That would be an example of a real bad idea.

Juice
 
  #8  
Old 11-24-04, 06:00 PM
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One quick clarification: If you touch a hot AC wire, no matter whether you're touching anything else or not, I think you'll find you'll get a shock. As long as you aren't providing a path to a good return source, you won't likely be electrocuted. Try standing on your rubber mat and touching an electric fence. AC has a rather uncomfortable tingle to it. With DC you may not get any shock. I've never had any experience...

Doug M.
 
  #9  
Old 11-24-04, 06:04 PM
SkyKing
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Get a "friend" to pee on it and they will agree it doesn't feel good either. Rubber soled shoes, in my younger days I remember losing feeling in my arm because of an electric fence. I would tend to agree with dougm.
 
  #10  
Old 11-26-04, 09:41 AM
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All very interesting......but in the example where I touch a hot wire and I'm standing on a rubber mat and I'm completely "grounded," how does the electricity "know" that there is no path to ground or a return to neutral if it doesn't go through me first? Know what I mean? How does it know what's at the end of the path (puddle or rubber mat under my feet if I touch with my finger) if it doesn't conduct through the path first? That's why I don't understand why if someone touched any hot wire they wouldn't at least get zapped for a millisecond until the electricity "figured out" it had no place to go by going through me.

Speaking of peeing on an electrical fence, Mythbusters did an episode where they tried to find out if the following myth was true: If a subway worker peed on the third rail of an underground electric subway train, would he get electrocuted? After much experimentation, the answer is yes, it "could" happen, but you would have to have an extremely (unhumanly) strong urine stream in order for the electricty to have a path to follow to your body. You wanted to know, right?

Again, guys, this is all theoretical. I would never ever ever do this at home.
 
  #11  
Old 11-26-04, 09:46 AM
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I'm not talking about the third rail. I'm talking about an electric fence. And yes, it would travel back up your urine. I've seen it happen (stupid friends).

AC current will shock you regardless if your grounded or not. Proof is in the pudding. But I'm not suggesting you should try.
 
  #12  
Old 11-26-04, 10:40 AM
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If you aren't 'grounded' you won't get a shock working on a live electrical line. As proof this try to watch a episode of 'The most dangerous jobs in the world'. One of them shows some guys working on a 500,000 volt line. They get on from a helicopter. As they approach the line they have a bonding stick that is drawing an arc about 2 feet long. After they get bonded to the line they are working on it with only thin gloves which offers absolutly no protection from a half a megavolt. They are usually weaving in new metal as the stranded conductors tend to shed them. As long as they don't get within about 30 feet from the metal line support towers they are safe. If something bad happens you would get instantly vaporized.

I know someone who is a lineman for the local power company. He says he routinely works on 8 to 12 KV lines from a bucket truck with only thin rubber gloves while the lines are live. I said that I would be uncomfortable doing that. He said that he would be uncomfortable working near a 480 volt 3 phase panel while it's open. I do that sometimes. I guess it's all what you are used to doing. Eight hundred amps of 480 volts will sound like a cherry bomb going off when you get a phase to phase short. That I know that from personal experience.
 
  #13  
Old 11-29-04, 07:36 AM
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As far as getting a shock while NOT in contact with any ground or neutral source, I have done a lot of live work on 120v single phase. I have personally grabbed one single hot conductor, with shoes on standing on a carpeted wooden floor and had no sensation whatsoever of electrical shock. Nothing. Nada.

As far as juice "knowing" where to go, electrical current doesn't. It is the process of applying pressure to one end of a wire (voltage source). When there is a ground source or a neutral "return path", the conductor molecules (usually copper or aluminum) give off an extra electron from its outer shell. That is passed along to the next molecule downstream (opposite direction from the pressure source), which forces it to give off it's extra electron, which it passes along to the next downstream molecule, etc., etc. If it has nowhere to "go", it will not pass electrons from one molecule to the next.

Voltage is pressure. The higher the voltage, the higher the pressure. Think of it like a water pipe. The higher the pressure, the more forceful the flow of water. Same with electricity, only different!

After taking much electrical theory in college, I can't think of a better way to describe this.

Juice
 
  #14  
Old 11-29-04, 07:39 PM
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Ohm's law in action!

re: the rubber mat question. To be " electricuted " means to suffer injury or death as a result of electical current passing through some par of your body.

For one thing, it depends on what part of your body, but that's another post.


In general, if I remember, a current in the neighborhood of 100 to 300 milliamps ( 0.1 to 0.3 amps) may cause ventricular fibrillation, which means your heart goes bananas and if not fixed right away you die.

Lower current may cause tingling, involuntary mucsle contraction, etc. but not cause injury if you get off it soon enough. At some level, the current is low enough that you don't feel it at all.

Higher current may cause burning of tissues, burns in internal organs which is not good, and it may cause your heart to stop . This is not good but can be restarted if you have help.


So, what determines how much current actually flows when you touch a live wire? Mr. Ohm. 120 volts divided by the resistance of your body = amps.

What is body resistance? Dry skin can be quite high. Sweaty skin can be much lower. One current penetrates the skin, the body is mostly water and current flows readily. The exact path current flows through is determined partly by mother nature, but also partly by which two body parts are touching the hot and the ground.



re: the hair dryer in the bathtub. The current would have multiple paths to get from the hot to the neutral and ground. First, it could flow immediately inside the dryer through the water from one wire to the other. Second, it could flow from the hot wire through the water all the way to where the water pipe comes in contact with ground. ( Remember, the cold water supply pipe may be grounded, but the DRAIN pipe is not. It might be steel or it might be plastic.) Third, in any of these scenarios, your body resistance may become part of the path to ground.

BOTTOM LINE: Don't try this at home.
 
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