Shocking Yourself - Batteries vs. Wires

[Danoff]

Ok, stupid question, which I no doubt could find the answer to if I cared enough. But hopefully one of you knows the answer and can quickly put my curiosity to rest.

Why is it that if I touch a couple of wires with high voltage running through them I'll get shocked, but if I touch both ends of a battery nothing happens. This is even the case with car batteries (right? I'm not sure I've ever tried that). I can come up with an answer for either scenario, but not one that seems to encompass both scenarios.

I was dealing with some electrical wiring in my house the other day and was being careful to flip the breaker before doing anything and started wondering about the mechanics behind getting shocked.

 

[Formula1Driver]

Maybe because you are standing on the ground and the circuit is completed through you, if you were floating, I am pretty sure you can tough any wire with any voltage and not feel anything.

I could be wrong but thats what I got out of the grade 9 electricity unit.

 

[Danoff]

I'm talking about touching both ends. One hand on positive, one on negative and allowing the electricity to flow through you. Which I've done a million times with a AA and not thought about it because it never shocks me.

 

[dylansan]

Perhaps because it's just a lame-o AA battery? Did you think they were powerful enough to shock you?

 

[Robin]

I think the charge just passes through you back to the batteries negative (using power in the process)... I think its just because the current is so tiny that you don't really feel it, you may feel a tingle in your finger but 1.2V from an AA ain't gonna stop your heart!.... luckly!

Work up the battery voltage chain and report your findings back to us Danoff

Robin

 

[Danoff]

Well I could go hug my car battery. But I kinda doubt that would do anything either.

I know that if you put a 9V on your tongue you can get shocked. But it seems like that's just a function of how conductive your fingers are vs. your saliva. Home electricity (which is what I was playing with) is substantially higher voltage. But, and I guess this is where my knowledge breaks down, does higher voltage require less conductivity?

 

[HACKr]

You would need about 18 AA's chained together to even begin to feel something.

EDIT: Resistance < LOTS of power.

 

[Slick Rick]

Why is it that if I touch a couple of wires with high voltage running through them I'll get shocked, but if I touch both ends of a battery nothing happens. This is even the case with car batteries (right? I'm not sure I've ever tried that). I can come up with an answer for either scenario, but not one that seems to encompass both scenarios.

Did you try at the same time. If you had sweaty hands with one and not the other it would make a difference.

 

[Boundary Layer]

Voltage is analogous to potential energy in physics - a rock that isn't rolling can't strike and kill you. But let that rock roll down a slope and you've got a different problem...

I'm no whiz when it comes to electricals or electronics or the like, but my gut feeling is that it has as much to do with the amperage flowing through you as the voltage by the relation P=IV.

Some googling will probably turn up the lethal dose in watts (a unit of power, for the lay) for an average adult male.


edit: a re-read reveals that my reply repeats the reason raised by Robin.... more r words


It must have to do with the electrical conductivity of human flesh. You can make a ghetto car battery handle by bridging a wrench across the top terminals (it'll weld itself in place) so it's certainly not for a lack of voltage that you don't get yourself hurt.

Related.... you can definitely shock yourself with just two AA's. Those badminton racket style bug zappers pack quite a punch, enough that my finger was temporarily stuck to the 'strings' when I decided to touch it and was numb for about half hour afterwards. I've gotta take one of them apart to see how it works - there's definitely a capacitor or two in there because it'll still shock you a few seconds after you turn it off.

 

[Kylehnat]

I'm pretty sure you can fatally shock yourself using batteries, but you need a whole bunch of them...so I'm going to go with voltage on this one. You also need a fair amount of current, but batteries in series will build that up, too.

 

[Omnis]

Perhaps it's because wires are grounded at another location, whereas batteries are not.

 

[Boundary Layer]

Perhaps it's because wires are grounded at another location, whereas batteries are not.

Either way you are the path of least resistance, the current should regulate itself to the net resistance of the circuit if a stable voltage source is present. Ohm's Law, remember: V=IR

 

[Robin]

Well I could go hug my car battery. But I kinda doubt that would do anything either.

I think that a car battery would actually hurt if you did that so please don't! Eventhough the voltage is meant to be 12V I think the batteries huge capacity of electricity going through your body would be dangerous!

I know that if you put a 9V on your tongue you can get shocked. But it seems like that's just a function of how conductive your fingers are vs. your saliva. Home electricity (which is what I was playing with) is substantially higher voltage. But, and I guess this is where my knowledge breaks down, does higher voltage require less conductivity?

Your right, the conductive solution makes a difference, the skin on our fingers is quite thick.. if you had wet hands or put it on you tounge its easier for the charge to flow.. As for your question I don't really know but I would guess yes... if you hold a pylon with any bit of your body thick or thin your fried!

When I was a kid I took apart a disposable camera and stupidly washed it in the sink when I was doing it just for fun (tut! the things you do when your young!)....

I got a really bad shock with a huge blue flash and it left a blister on my finger, funnily enough it wasn't the battery it was the flashes capacitor (a lot higher voltage than the battery) discharging all in one go into my finger using the water...

Robin

 

[Car-less]

Why is it that if I touch a couple of wires with high voltage running through them I'll get shocked, but if I touch both ends of a battery nothing happens. This is even the case with car batteries (right? I'm not sure I've ever tried that). I can come up with an answer for either scenario, but not one that seems to encompass both scenarios.

I've never thought of trying it accross a car battery, but I have unplugged one of the HT leads whilst the engine was running. Not to be recommended.

I'm talking about touching both ends. One hand on positive, one on negative and allowing the electricity to flow through you. Which I've done a million times with a AA and not thought about it because it never shocks me.

Ever tried clubbing someone to death with a toothpick?
Gather together enough AA batteries to boil a kettle and you might get somewhere!

 

[Omnis]

Either way you are the path of least resistance, the current should regulate itself to the net resistance of the circuit if a stable voltage source is present. Ohm's Law, remember: V=IR

Yeah, but isn't it theoretically possible to create a ground loop out of yourself?

edit: Oh, and capacitors aren't fun. I exploded an op-amp with a badly-wired cap.

 

[Perfect Balance]

Well I could go hug my car battery. But I kinda doubt that would do anything either.

I think that a car battery would actually hurt if you did that so please don't! Eventhough the voltage is meant to be 12V I think the batteries huge capacity of electricity going through your body would be dangerous!

I've never thought of trying it accross a car battery, but I have unplugged one of the HT leads whilst the engine was running. Not to be recommended.

I know you can touch both terminals on a car battery at the same time without a problem. It's always scary to try, even when you've done it before, but it doesn't do anything.

 

[Slicks]

Okay, I'll make an attempt at this.

Conductivity is a matter of voltage - not amperage.

This is the reason that a AA won't shock you, alone. This is the reason that a car battery won't shock you when you touch both terminals. This is the reason that I can touch both terminals of an 8D marine battery (12 volts, 1400 cranking amps, and weighing in at close to 100 lbs) without being fried.

But higher voltages can, and will fry you. The type of current is not relevant either - It can be DC, or AC.

You'd probably feel a little bit from a 24 volt source. More with a 36 volt source, and so on. I can say from experience that a 64 volt DC system can and will make you wish you hadn't made the connection. Capacators, similarly, build and maintain a voltage level that is higher than the input.

But it's when it gets to residential electricity levels that it gets lethal. At 120VAC, it takes less than an amp to stop your heart.

So be careful when you're working with any high voltage application! Disconnect that positive battery lead, or turn off the breaker. It may save you some discomfort, or it may save your life!

As an aside, with good connectivity & amperage available, a 12V source can make a nice big spark. Short out a previously mentioned 8D battery with a conveniently misplaced battery jumper or wrench, and it will attempt to weld itself to the terminals before flying off.

 

[Alfaholic]

It's maths.

V=IR means that I = V/R

V is voltage, which is low for an AA battery.

I = amps, i.e. current measured per second - how many electrons pass through you per second. Current is what shocks you, the higher the amps, and the longer it's flowing, the more coulombs flow through you and the worse the shock. R is resistance to that flowing current.

Your body is not generally regarded as a good conductor, i.e. it has high resistance. From I=V/R, we can see that if resistance (R) is high, Current will be low unless voltage is high, hence less shock. So the reason the AA battery doesn't shock you is it does not have sufficient voltage (think pressure) to push a noticeable amount of current through you. I'd expect a car battery is also not powerful enough but I ain't gonna try it..... I think you only need half an amp to be fatal, which with a 12V battery requires a resistance of 24 ohms or less to exceed. I have no idea what the resistance of a human body is from one hand to the other, though I'd hope it's more than 24 ohms.

Also, Saliva has a higher water content and high salt content, which I assume makes it more conductive than the fleshy path from your thumb to your finger which the AA battery is trying to pass through. Also remember a 9V battery on your tongue only has a short distance of saliva to push through, hence less total resistance. You might feel something if you get two copper wires, connect one to each terminal of the AA battery, then place the other ends very close to eachother on your finger so that the current has a short path to travel through your skin. This shorter distance will reduce R, allowing you to feel more I.

As for AC and DC, I have heard that AC is generally safer than DC because the current reversal in AC means that your muscles will flex then release, so if you grab two wires and thus complete an AC circuit, you'll be thrown off involuntarily, reducing the exposure to amps. DC will make you clench the wires and be unable to let go, so you will continue to fry until the supply is turned off. I'm not sure though if this is actually true, or if it's an urban myth.

 

[Danoff]

From I=V/R, we can see that if resistance (R) is high, Current will be low unless voltage is high, hence less shock. So the reason the AA battery doesn't shock you is it does not have sufficient voltage (think pressure) to push a noticeable amount of current through you.

I believe that explains it quite well. Thanks. This thread can die now (unless someone else has anything to add).

 

[GrumpEone]

The most common reason for deaths, with a 120V AC system, is not the power (wattage), but the 60Hz oscillation of the AC (Alternating Current). If it runs from one hand to the other, the shortest path runs right through your heart, and the oscillation is enough to make your heart skip a beat, or stop all together. If that same power just hits one hand (both wires touching one hand), you will get a poke that will knock you on you butt, but it will never kill you, at 120V. It just makes your hand in essence a jumper. So if you ever work on a live 120V AC circuit, only use one hand, and you won't die.

Now a human body has a constant fluctuation of resistance, around Millions of Ohms, thus 9V batteries' power is just dissapated, mainly due to the lack of conductivity (of the human body), but also the high-resistance, and the low voltage/ current of the battery. The Voltage determines how easily the current passes through a conductor, and the current detremines how many electrons pass through that conductor, an extreme in either though can kill you. Power (P) figures into it as well, which is the combination of both Voltage (E) and Current (I), the formula is P = E * I and is expressed in Watts. For example, you have a 100W Light bulb that runs on 120V it draws only 0.833 A or 5/6ths of an Amp.

How this info is useful for you, though it took me a bit to remeber those HS Electronics Classes...

 

[YSSMAN]

As a joke when I was in the sixth grade my friends dared me to attach batteries to my braces. Its was a little tingly.

That is all...

 

[GrumpEone]

As a joke when I was in the sixth grade my friends dared me to attach batteries to my braces. Its was a little tingly.

That is all...

lol...9 volts of tingling, I used to see if a 9V battery had juice left, just by touching it to my tongue.

When I was in ninth grade I asked my uncle, who was an electrical engineer, to get me the biggest capacitor that he could. He gave me one a little bigger than a 3-Litre bottle. I charged it in the electronics lab, and after class discharged it against a metal file cabinet. With a pow, the beautiful blue light ripped a gash in the file cabinet, about 4" Long and almost 1/2" wide. It was well worth the suspension! lol

 

[somebody]

Before anybody goes grabbing hold of batteries left, right and centre, try reading this. I know it's a Wikipedia entry, but that doesn't mean it is a complete crock.

 

[Blake]

I know it's a Wikipedia entry, but that doesn't mean it is a complete crock.

Shocking, isn’t it?