Electrocution at Lake Pleasant, AZ
- Thread starter AlastairLC
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Roy.
Could it be that the old saying and your thoughts are both correct? Since Electricity “seeks” every path to ground, the one it finally takes and discovers successful turns out to be the “easiest path it found”?
Just early morning philosophical exploration. I think I may need coffee.
Could it be that the old saying and your thoughts are both correct? Since Electricity “seeks” every path to ground, the one it finally takes and discovers successful turns out to be the “easiest path it found”?
Just early morning philosophical exploration. I think I may need coffee.
Electricity takes the path of least resistance. This is not really true, the current will divide among all paths according to the relative resistance of each path.
This is otherwise known as a parallel circuit. The formula for resistance in a parallel circuit is 1/r + 1/r + 1/r = R. (For as many resistors in the circuit).
In a highly conductive solution the current takes the shortest fastest least resistant return path, most of the current will flow around the human and not through the human as the body offers more resistance than the surrounding water.
In a less conductive solution it spreads out, a human body offers less resistance than freshwater thus when a human is in the path, the current flows through the human and less current through the water.
It's unlikely that a cord end dropped in the water would cause this. It has too little exposed conductor and freshwater is a poor conductor.
More likely someone has swapped the hot and ground wires. A conventional (thermal) circuit breaker is unlikely to trip because it would experience a light load. This is another reason why the AC ground should never be connected to the DC ground.
Ken
More likely someone has swapped the hot and ground wires. A conventional (thermal) circuit breaker is unlikely to trip because it would experience a light load. This is another reason why the AC ground should never be connected to the DC ground.
Ken
Scorpion Bay (where it happened) does not prohibit swimming in the marina, but maybe that will change now.
While I don’t dip in the slip, the young man who cleans Bells Zee's hull bottom does. Now I’m worrying about him.
While I don’t dip in the slip, the young man who cleans Bells Zee's hull bottom does. Now I’m worrying about him.
It is the AC current that is a problem. It is much more dangerous than DC at low current levels.
If away from a source of AC power, then you should be safe from AC. How far depends in part on the salinity of the water.
Swimming away from a marina with a generator running, presents another problem CO. Depending on the conditions the exhaust can build up near the swimmer. This was a problem with many house boats, those floating trailers. Don't know about AC threat with a generator running.
I'd like to know the answer to that, and also about inverters.
I'm going to check out the grounds on my boat again.
Almost all electrocutions everywhere are with AC current. The electric chair was invented as a marketing ploy to scare people away from AC.
My .02 on why fresh water is more dangerous for ESD
You have to consider this is a 3D problem. If you put two parallel plates in the water and applied a voltage, current would flow between the plates depending on the concentration of charge carriers in the water. More charge carriers equals higher conductance (or lower resistance) so equals higher current.
Now put a single hot electrode in the water with a ground reference but the other "electrode" is the earth. Ie, the other electrode is everything that is grounded which includes the actual ground under the marina.
Remember its a 3D problem and conductance is proportional to the number of available charge carriers. First consider some small distance from the electrode and if the electrode is near the surface, this forms a half sphere. Since the diameter of the sphere in this case is small, the volume in the sphere is small so the number of charge carriers is also small. Low number of charge carriers is higher resistance.
But as you move farther out, the volume of the sphere increases with the cube of distance. This means that the number of charge carriers is also increasing as you move away from the source by the cube of distance. Since conductance (1/resistance) is proportional to the number of charge carriers, the 3D conductance "seen" from the hot electrode increases very rapidly as you move away from the hot electrode. Or put another way, the 3D resistance decreases very rapidly as you move away from the electrode and in fact decreases with the cube of distance.
Now look at the volts per distance as current moves away from the hot electrode. The 3D resistance is dropping with the cube of distance away from the electrode so by ohms law, the voltage per distance (electric field) is also dropping with the cube of distance.
What can you conclude from this.. In salt water, the charge carrier density is high so the 3D electric field spreading out in all directions from the hot electrode drops off very quickly and may be dangerous for only a few inches.
But in fresh water, the charge carrier density is much lower so the 3D electric field from the hot electrode spreading out in all direction extends out to a much larger distance than in salt water. Ie, instead of a few inches in salt water, the dangerous level of field might extend out many feet in fresh water.
The danger is when the swimmer moves into that electric field which causes a voltage potential across the body. Fresh water will have a much larger dangerous electric field distance from the electrode than salt water.
This also means that if the swimmer simply moved away from the hot electrode by a short distance, they could be safe. Remember the electric field is decreasing with the cube of distance away from the hot electrode. But it also means that as the swimmer moves toward the hot electrode, the electric field would be increasing rapidly.
You have to consider this is a 3D problem. If you put two parallel plates in the water and applied a voltage, current would flow between the plates depending on the concentration of charge carriers in the water. More charge carriers equals higher conductance (or lower resistance) so equals higher current.
Now put a single hot electrode in the water with a ground reference but the other "electrode" is the earth. Ie, the other electrode is everything that is grounded which includes the actual ground under the marina.
Remember its a 3D problem and conductance is proportional to the number of available charge carriers. First consider some small distance from the electrode and if the electrode is near the surface, this forms a half sphere. Since the diameter of the sphere in this case is small, the volume in the sphere is small so the number of charge carriers is also small. Low number of charge carriers is higher resistance.
But as you move farther out, the volume of the sphere increases with the cube of distance. This means that the number of charge carriers is also increasing as you move away from the source by the cube of distance. Since conductance (1/resistance) is proportional to the number of charge carriers, the 3D conductance "seen" from the hot electrode increases very rapidly as you move away from the hot electrode. Or put another way, the 3D resistance decreases very rapidly as you move away from the electrode and in fact decreases with the cube of distance.
Now look at the volts per distance as current moves away from the hot electrode. The 3D resistance is dropping with the cube of distance away from the electrode so by ohms law, the voltage per distance (electric field) is also dropping with the cube of distance.
What can you conclude from this.. In salt water, the charge carrier density is high so the 3D electric field spreading out in all directions from the hot electrode drops off very quickly and may be dangerous for only a few inches.
But in fresh water, the charge carrier density is much lower so the 3D electric field from the hot electrode spreading out in all direction extends out to a much larger distance than in salt water. Ie, instead of a few inches in salt water, the dangerous level of field might extend out many feet in fresh water.
The danger is when the swimmer moves into that electric field which causes a voltage potential across the body. Fresh water will have a much larger dangerous electric field distance from the electrode than salt water.
This also means that if the swimmer simply moved away from the hot electrode by a short distance, they could be safe. Remember the electric field is decreasing with the cube of distance away from the hot electrode. But it also means that as the swimmer moves toward the hot electrode, the electric field would be increasing rapidly.
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Yes, AC current is the concern. If swimming away from the marina, assuming no inverter or generator, then the only voltage source is the battery banks. The current from the battery should be in a continuous loop from one terminal over the boat’s wiring and back to the other terminal. Even if there is a fault, say allowing current to travel out a through hull and in the prop shaft the maximum potential between those two points is only the voltage of the battery, which is not enough to do any harm.
With an inverter or generator running the voltage is higher, but the path of the current would still only be along those same paths. The risk at a marina is current traveling from a boat’s underwater metal back to ground at the marina dock. Get in between (or near) that path and you become part of the circuit. With an inverter/generator that path isn’t looking to get to some dock or earth, just across the boat itself, since that is boat the source and sink of the current. So the dangerous areas should be significantly smaller than shore power.
Thank you for that info. I am curious about the example of a generator - either diesel or portable gas. You have a hot wire to the load and a neutral coming back to the generator. Where does the ground go? Or in the case of the portable is it even grounded?
Roys, I agree that this situation is not likely to result in burns. Drowning is from the 60hz messing with the heart and muscle function somehow and the current can be WAY lower than what is needed to cause a burn.
Just guessing.. but the burn thing might be more related to fodder for the future law suit. But.. I could be wrong..
Just guessing.. but the burn thing might be more related to fodder for the future law suit. But.. I could be wrong..
[QUOTE="walt, post: 1645753, member: 64128"
This also means that if the swimmer simply moved away from the hot electrode by a short distance, they could be safe. Remember the electric field is decreasing with the cube of distance away from the hot electrode. But it also means that as the swimmer moves toward the hot electrode, the electric field would be increasing rapidly.
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Once the current crosses through their body and the current passes through the chest, it is all over. The muscles contract and the heart stops. Happens much too quickly to move away, if you just jump in. The woman with them stuck her feet in the water and the current passed through her ankles and burn them, she was able to pull her legs out of the water.
This also means that if the swimmer simply moved away from the hot electrode by a short distance, they could be safe. Remember the electric field is decreasing with the cube of distance away from the hot electrode. But it also means that as the swimmer moves toward the hot electrode, the electric field would be increasing rapidly.
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Once the current crosses through their body and the current passes through the chest, it is all over. The muscles contract and the heart stops. Happens much too quickly to move away, if you just jump in. The woman with them stuck her feet in the water and the current passed through her ankles and burn them, she was able to pull her legs out of the water.
The ground should go back from the outlets to the generator, at least in the case of permanently mounted generators. Doing this ensures that a fault that puts voltage on anything like a metal device case is carried back to the source, and can trip a breaker, rather than presenting a shock hazard. I’m not sure about portable ones, but it seems the same concepts would apply.
Disclaimer: I’m not a professional electrician. The above is my understanding of the correct procedure based on what I’ve read in Nigel Calder’s book and elsewhere.
In fact, the field can be very weak and still inhibit your ability to swim. It does not have to stop your heart, only challenge locomotion and breathing. There have been cases of field extending out from the dock toward deeper water as much as 50-100 feet still being lethal.