Stray Voltage in a Lake

[grantcool]

I just read Mike's newsletter about the lake. We've all seen the idiot on a job who grabs a live bussbar to show that you can't be shocked if you're not grounded.
Can someone explain how a person gets electrocuted while immersed in water and not touching a ground? I thought current had to pass from point A to point B through a human body?
How does that work if current is present at every point the surrounding water is touching?

 

[LJSMITH1]

Here is another accident in 1998. I can't find the followup, but I am sure it probably had to do something with the local docks.

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/1998/07/20/MNR1BA5.DTL

Stray current electrocutions don't require the person to be touching a grounded structure. You could still have loss of muscle control and drown.

 

[K8MHZ]

I just read Mike's newsletter about the lake. We've all seen the idiot on a job who grabs a live bussbar to show that you can't be shocked if you're not grounded.
Can someone explain how a person gets electrocuted while immersed in water and not touching a ground? I thought current had to pass from point A to point B through a human body?
How does that work if current is present at every point the surrounding water is touching?

Water, like earth, will present a voltage gradient. That gradient may present a lethal voltage potential from one part of a person's body to another.

If you have any training with downed power lines, you should be familiar with voltage gradients. They are the reason people are trained to shuffle, not walk when near downed power lines. If the earth below you has a gradient of 500 volts per foot, a two foot step would present a 1000 volt potential between the bottoms of your feet.

While immersed in water, the gradient can be much less and be lethal. 50 volts per foot is enough to kill some people and render most incapable of controlling their movements.

Usually we don't see such a high gradient in water and the voltage potential is between the ions in the water and something grounded, like the bottom of a lake or a piece of metal on a dock or a pool.

 

[hurk27]

I just read Mike's newsletter about the lake. We've all seen the idiot on a job who grabs a live bussbar to show that you can't be shocked if you're not grounded.
Can someone explain how a person gets electrocuted while immersed in water and not touching a ground? I thought current had to pass from point A to point B through a human body?
How does that work if current is present at every point the surrounding water is touching?

As mark has given a great explanation, I can only try to add, that when thinking about the theory's of this, think in 3 dimensions, not 2, as the current will travel in 3 dimensions. and check out this thread: Time To Eat Crow

but add to it, with the added resistance of fresh water, which can be higher then the resistance of Earth, so the voltage shells will be much larger and can present voltage gradients father out from the injected point, but from there much of everything else will apply in that thread.