OK, so we all know not to use the toaster in the bath. And I’m sure the hot tub is no place for a hair dryer. But what exactly is the harmful potential of electricity in ratio to the amount of water. For instance, I’m not sure if I’d try the ol toaster in a pool, but you know, If I’m on one side of a lake and the toaster is on the other…I’m pretty ok, right? I mean, surely if you’re playing in the atlantic and someone drops a radio in the pacific, you aren’t going to get shocked.
The electricity will take the path of least resistance which is usually part of the equipment itself ( like the nuetral or the equipment ground). You wouldn`t be hurt by such an incidence unless you touched the object in question and you were grounded or somehow were completing the circuit.
Unlikely that these scenarios would work against you unless you were in the immediate vacinity of the appliance or in contact with it.
That always made me wonder… Why should we let someone live if they would use the hair dryer in the shower? I mean, that is like hanging your clothes out to dry in a rain storm! Seems like it would do the human race a favor to get rid of those genes.
No, silly.
Well actually yes, if there is no water running.
In reality,
The definition of “using” requires you to be in the “immediate vicinity” of the dryer. If you are holding the dryer as the water is shorting out the circuit, then you become the path to ground and you will be in trouble.
If a radio falls into the pool and the fuse/breaker/GFCI dont trip you could become the pathway for the electrons back to ground potential if your body is grounded and the resistance is relatively low. If you are floating in the water I dont see how you could get shocked. When you touch something in the water or try to leave the pool your resistance changes and you could feel something then. There is really no way to tell if it would kill you or not.
There is a common misconception that was repeated by whuckfistle above: “Electricity will take the path of least resistance.” This is patently, and dangerously, false. Electricity will take every path and a moments thought will render this statement obvious. Consider the monitor that you are using to view this message: Inside is a circuit board with many etched paths that connect various electronic components together. In order for this to work correctly, all components must receive the proper voltage. If electricity actually took the path of least resistance, only a portion of the components would see any voltage at all, the rest would never be energized.
As to the dangers of this misconception, a number of years ago, utilities required that all boom and bucket trucks be grounded if the trucks were to be used in proximity to energized lines. The thinking was that, should this equipment contact an energized conductor, the ground fault would cause the overcurrent relays in the feeder breakers to trip the breaker, thus rendering the conductors de-energized and preventing further risk to health and property. While this generally worked well for its intended purpose, an undesirable side effect was that it gave the utility workers and the general public a false sense of security in that they felt, since the truck was grounded, no harm could befall them should it get into the lines. The reality is that not only does the electricity travel through the installed ground, but it also travels through the outriggers (stiff legs) as well as anything touching both the truck and the ground, including people! I personally knew (key word being knew) one lineman that was leaning against a truck when somebody stuck the boom into the line.
Additionally, there is ‘step potential’ to be considered (if you weren’t scared before, you will be soon) which is basically the difference in potential dependent on distance from the ‘source’. A.B. Chance released a training video a number of years ago to illustrate step potential. In the video, a number of mannequins were placed, as if standing normally, various distances from a switch (i believe it was within a 15’ - 20’ radius). Each mannequin was rigged with a lightbulb in the genital area as an indicator of current flow. A switching fault was simulated (i believe the voltage used was 12,470) and with the exception of the mannequin standing on the switching platform, all of the other mannequins lit up; some to the extent that the bulbs exploded. What this was meant to illustrate was that, depending on how close you were to where the fault occured, the difference in the potential between one foot and the other was enough to allow the electricity to flow up one leg and down the other. So, if you see a wire on the ground spitting and burning, stay as far away from it as possible.
First, the main problem with touching a live appliance when you’re in water is that you are almost certainly very nicely grounded, serving to complete the circuit and taking 100% of the juice. If someone drops a toaster in the tub and you don’t touch the toaster, you are subject merely to the amount of current that happens to go through you as it is trying to find ground.
To amplify, the electricity will take a path proportional to the resistance. That is, supposed you have two grounded wires, one twice as long as the other, and apply equal voltage to each wire. The longer wire will carry half the current as the shorter one.
A toaster dropped in the ocean will cause current from the toaster to ground. The shortest distance and therefore lowest resistance will be straight down, but a path twice as long through the water will carry about half that current, and one 10 times as long will carry 1/10, and so forth. Someone a mile away would probably find the current to be in noise level. The math in my explanation is simplified, but the point is that there will be current everywhere in the water decreasing with the distance from the toaster.
How far away you have to be to be safe depends on the voltage you’re starting with and the composition of the water (salt water conducts electricity mighty fine). You might not even notice if you were diving in the deep end of a pool when someone dropped a toaster in the shallow end, but I sure wouldn’t want to be there for a lightning strike. I also don’t know how many amps for what time a human can survive.
I have an EE friend who has told me that the conductivity of fresh water is really quite low, and thus the concern about using electrical devices near it is overrated. Was he pulling my leg?
To continue CookingWithGas’s comments, here’s a rough list of the effects of current on the body (from AC Power Systems Handbook, J. Whitaker, Table 9.1):
Current Effect
< 1mA Little or none
> 3mA Painful shock
> 10mA Local muscle contractions; 2.5% chance of 'freezing'
> 15mA 50% chance of 'freezing'
> 30mA Breathing difficult; loss of consciousness possible
50 - 100 mA Possible ventricular fibrillation
100 - 200 mA Certain ventricular fibrillation
> 200 mA Severe burns, contractions; heart more apt to stop
than to go into fibrillation
> a few amps Irreperable damage to body tissue
The ‘freezing’ effect means that you will be unable to let go of the circuit; this is potentially a very dangerous situation. The typical amount of time until electrocution is on the order of 5-10 sec for currents less than 100 mA, so being stuck to the source is deadly at even low current levels. That’s part of the rationale for the protection scheme described by octothorpe - those working on the circuit may be unable to disconnect themselves from it. Of course, if you’re immersed in the water, you’re not really getting away from the source any time soon.
Note that at high current levels the heart simply stops, which is why it’s possible to survive a lightning strike even if it goes through your body (it can restart soon after, the principle behind a defibrillator). Though the damage to other organs might be enough to kill you.
As to what sort of things create this level of current flow, consider that the hand-to-hand resistance of a normal dry human is on the order of 500k ohms. Since Current = Voltage / Resistance, we can estimate that you’d need > 25,000 volts to get really dangerous.
If you’re in water, the resistance is going to go way down since there’s much more of your body in contact with the conductor. For a toaster or other household appliance, and an American line voltage of 120V, you only need to get resistance down to the 10k ohm level to be dangerous, and I imagine an immersed body can easily get that level.
He should have said pure water. Nothing else in it. But real water has stuff in it. So natural bodies of water, swimming pools, bath tubs, etc. conduct plenty well enough. Lot’s of stats on that.
Just because someone has a degree in something doesn’t mean they remember all the facts. (I taught at the the college level. I saw the answers the graduates-to-be put down on tests. Egads.)
Even water with crap in it makes a fairly lousy conductor, as conductors go. But it makes an even worse insulator. Compared to copper, water is a lousy conductor. Compare it to wood and it makes a really lousy insulator (i.e. compared to wood it’s a really good conductor). It’s all a matter of how you look at it.
In some ways the danger of water is overrated, especially the hollywood versions. The thing about electricity though is that it’s an odds game. If you get a shock through your chest at just the right time during your heart’s cycle, you’ll throw your heartbeat out of whack, and unless someone happens to be standing next to you with a portable defib unit, your chances of seeing the next day are mighty slim.
It’s a lot like russian roulette. The chances of you dying from one spin are relatively low, but if chances don’t work out in your favor the consequences are pretty extreme.
By the way, the amount of current that is thought to be “safe” to pass through your chest is only 5 mA (for obvious reasons we haven’t done a great deal of testing on this, but that’s the number that the experts have presently agreed on). Even with a relatively poor conductor, it’s very easy to get that much current to flow. Electric chairs, by comparison, typically put about 5 amps (1000 times more current than 5 mA) through you. If you can get 5 amps flowing through you, you don’t need to worry so much about whether or not it interrupts your heartbeat. The heat generated will cook you to death.
Less than 5 mA won’t kill you. 5 amps is guaranteed to kill you. Everything in the middle is an odds game.
Octothorpe - While what you said is true, I was trying to simplify the point down. I oversimplified. “More electricity will flow through the path with the least resistance.” Would have been more accurate. I happen to be an electrician and I understand why you jumped on that statement.
Practically, in the case of the appliance, the household type circuit that it would be plugged into at the time of use will not allow enough amps for the wild paths of series and series parallel resistances to occur. Hopefully the fuse or breaker will have tripped long before that because a majority of the current will have gone right from the nearest hot conductor - through the water- then to the grounded part of the appliance thereby causing the fuse or breaker to open.
If your fuse or breaker doesn`t open - all bets are off.
Your story of the grounded truck makes sense too. With voltages that high, the paths to ground can be very unpredictable. The truck itself, being grounded, should carry the current to ground safely. If someone is leaning against the truck while the fault occurs then they become part of the ground path in a parallel condition proportional to their body`s ground potential. The body will carry some current until the fault is cleared. Grounding the trucks is still a good idea otherwise the fault will take an unpredictable and/or unwanted path to ground.
whuckfistle, what octothorpe described was a nice anecdote in favor of insulated buckets, nothing more.
The idea of someone being electrocuted while touching a truck in contact with live high voltage wires is entirely plausible. The idea that the electrocution was in some way caused by the truck being grounded is utterly ridiculous.
The body in question would have recieved MORE current if the truck wasnt grounded. If the body was the only path to ground then most of the fault would have travelled throught the body. With the truck grounded, the body merely becomes a parallel path to ground until the fault clears. Big difference if youre the body.
Insulated buckets are great, but what if a line falls onto the truck and lands on the frame?
It only says the worker was electrocuted because he leaned against the truck and current went through him as well as the ground connection. Not because of the ground.
