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Old 08-25-2011, 12:10 PM   #16
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Quote:
Originally Posted by ddawg16 View Post
Your link is a bit lacking in details...

Then look up any of the numerous other case reports online.

Bottom line....if the swimmer is not 'touching' anything else in the water, they will NOT be shocked. In order to be shocked, there has to be a voltage across their body. If they are in the water and the water is at a 1000 Vac....their body will also be at that same potential......but as long as they don't touch something...there there is no current flow...and no shock.

This would be true if the water were completely isolated from ground, like in a plastic bathtub. However, water is somewhat conductive, and surrounded by the earth in a lake or swimming pool. An electrified conductor placed in a body of water surrounded by the earth will not raise the potential of the entire body of water to the voltage of the conductor. Instead, it creates a three dimensional electric field gradient surrounding the conductor. Because water is somewhat conductive, current certainly does flow. The closer you get to the conductor, the greater the voltage gradient (in volts per unit distance), and the greater the current density (in amps per unit area).

In the example you posted...I suspect they touched the boat or their feet touched the lake floor....

They did not, and that explanation is inconsistent with both the description from the survivor and the physics. Go read any of the numerous other reports of electric shock drownings. It's not uncommon, and a few survivors have given reports.

Case in point....have you ever seen the guys that work on high voltage lines? They use a helicoptor to drop them right on the line....do they get shocked? No. As they get close, they use a probe to get them and the chopper at the same potential...after that, they climb on.
That's not a comparable situation at all. They are not immersed in a semi-conductive medium surrounded by the earth.

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Old 08-29-2011, 12:52 AM   #17
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Due to the economy and weather, the number of pools we put in the past two years is half of the norm. Because the market and inflation has been so bad, our profit per pool is down about 35%. The cost to tear out and repour concrete would be about 6k. While that might seem like a few bucks to you, to me it is the difference between my daughter and son staying in college this year. So, although we are prepared to bite the bullet if necessary, I'm hoping to do some troubleshooting and fact gathering before renting a few jackhammers. Again, l a little less than one year ago the pool was bonded by a licensed electrician, according to the code that our county inspection office requires, and was signed off by the inspector. One year later, the customer reported that children in the pool on a hot summer night (our temperature hit 90 in June and hasn't dropped below since and we have had zero rain) were complaing that they were getting shocked when they touched any/all metal components. If removing the concrete is the only way to determine if there's a broken bond, I guess that's that. However, I don't want to go to that extreme only to find out the bonds are fine, there's just some weird static thing that takes place in salt pools when the werather is extremely hot and dry, or that yes, there was some danger but some well placed copper rods would remove any real dangers. Thanks for the suggestions from others as to exactly what and how to check - those things I can afford to get done
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Old 08-29-2011, 01:53 AM   #18
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Is being shocked in a properly bonded pool truly impossible or just improbable?


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Originally Posted by mpoulton View Post
That's not a comparable situation at all. They are not immersed in a semi-conductive medium surrounded by the earth.
If you are floating in the water and NOT touching anything....you can not be shocked. Your body will be at the same potential of the water. Period....

In all other cases of people beging shocked in a pool...they touched something...the side of the pool...a ladder...something.

To be shocked...there has to be a difference in potential....if you are in the water...and not touching anything...your body is at what ever the potential of the water is....it's that simple....

If you still disagree...then you need to explain the physics on how the person gets shocked.
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Old 08-29-2011, 12:00 PM   #19
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Quote:
Originally Posted by ddawg16 View Post
If you still disagree...then you need to explain the physics on how the person gets shocked.
I already did, and honestly it's fairly basic physics. If you've ever taken a college level E&M class this should be obvious. A question based on this actually showed up on one of my undergrad physics exams. Water is not a very good conductor, so when current flows through it, a voltage gradient occurs between any two points along the current flow vector. If a person is placed in the region of current flow, some of the current will flow through their body instead. You can model this mathematically based either on the current density and ratio of conductivities of the water and the body, or based on the voltage gradient and the conductivity of the body alone.

You are confusing yourself by making two incorrect assumptions: that no current is flowing through the water because it's all at the same potential (this is clearly not true - the body of water is literally grounded, so current definitely flows), and that the water is perfectly conductive so there is no voltage difference between any two points in the water (also not true - water is a fairly poor conductor).

If someone were floating in an electrically insulated insulated bath of liquid mercury, you could drop a hot conductor in there with no problem. But water is not as conductive as mercury, and pools/lakes are not isolated from ground.
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Old 08-29-2011, 01:27 PM   #20
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Is being shocked in a properly bonded pool truly impossible or just improbable?


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Originally Posted by mpoulton View Post
I already did, and honestly it's fairly basic physics. If you've ever taken a college level E&M class this should be obvious. A question based on this actually showed up on one of my undergrad physics exams. Water is not a very good conductor, so when current flows through it, a voltage gradient occurs between any two points along the current flow vector. If a person is placed in the region of current flow, some of the current will flow through their body instead. You can model this mathematically based either on the current density and ratio of conductivities of the water and the body, or based on the voltage gradient and the conductivity of the body alone.

You are confusing yourself by making two incorrect assumptions: that no current is flowing through the water because it's all at the same potential (this is clearly not true - the body of water is literally grounded, so current definitely flows), and that the water is perfectly conductive so there is no voltage difference between any two points in the water (also not true - water is a fairly poor conductor).

If someone were floating in an electrically insulated insulated bath of liquid mercury, you could drop a hot conductor in there with no problem. But water is not as conductive as mercury, and pools/lakes are not isolated from ground.
Was going for a EE degree...then changed over to CSE....Maxwell equations are not fun.

Anyway....you are correct about the gradiants....but in reality, the person is not going to get shocked...

I'm sure we both agree that the human body is a better conductor than the water that it is in (salt content of the body would be greater than that in a pool).....but not by much....

I agree...that the semi-conductive nature of water would create voltage gradiants along the 'length' of the volume....and a human body in that same length would create a 'bypass' path along the same length.

I think we can assume the following....with voltage being constant....the current capacity of the water is a function of the surface area of contact with the voltage source and volume of water.....

Now....lets assume that the swimmer is in a tube surrounded by water. One end of that tube has a high voltage applied to it...the other end grounded. At any given point along that tube, the water will be at x potential as referenced to ground. Assume we have 1000 volts on one end....then in the middle we would have about 500v....more or less....taking into consideration of coupling and the type of measureing device (high impeadance meter).

Now...lets toss in our swimmer....feet towards voltage source....head towards the ground. So, based on your position, he would get shocked because his feet would be close to 1000v and his head 0. Thats assuming that his body is more conductive than the water he is in. In such a narrow configuration (don't know of too many swimming pools shaped like a tube with 1000 volts on one end), yea, it might be possible to shocked.

But here is the real issue....as current enters his feet....and the potential starts to build across the body...the same current/voltage now wants to exit the body at every point along the body....hence, that voltage is now being shunted back into the water.

In a nutshell, the water is basically one big parallel resistor around the body. I guess if you created the above setup...it might be possible to shock a person....but it would take a very unique configuraton. Additionally, as the conductivity of the water goes down, so does the coupling of the voltage source go down.

So....unless the swimmer touches something that is much more conductive than the water he is in.....he is not going to get shocked.

I did some more checking.....and in all the references I found....it appears the person touched something to create a difference in potential.
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Old 08-29-2011, 01:39 PM   #21
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Very interesting reading, thanks for the debate on electrical energy with regards to a pool of water, but no matter how much you tell me I won't get shocked I sure won't be jumping in......

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Old 08-29-2011, 03:12 PM   #22
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Quote:
Originally Posted by ddawg16 View Post
But here is the real issue....as current enters his feet....and the potential starts to build across the body...the same current/voltage now wants to exit the body at every point along the body....hence, that voltage is now being shunted back into the water.

In a nutshell, the water is basically one big parallel resistor around the body.
This right here is the failure in your analysis. Yes, the water is a big parallel resistor - but that's irrelevant in a voltage-based calculation. The voltage gradient across the body is the same as the voltage gradient in the water, so current cannot be "shunted back into the water". It would have to flow against the voltage gradient... and there's a little Ohm's law problem with that.

By your logic, I should be able to touch both ends of an electrified heating element and not get shocked, because it's a big parallel resistor and the current that would go through my body would just flow through it instead. Of course that's not true. Go stick your hand in a toaster and see how it works out - you won't keep it in there long enough for it to get hot! The immersed swimmer is exactly the same configuration electrically. He's in parallel with a resistance that has a current flowing through it. Thus, current will also flow through the swimmer.

Which references did you find where swimmers were only shocked after touching things? Certainly there are plenty that involve contact with an electrified object (or a grounded object in electrified water), and it's definitely far worse to touch the electrified object, but it's not necessary. The original incident I posted did not involve touching anything. The narrative by the survivor was pretty clear that she was shocked while not touching anything. The sort of definitive list of incidents is maintained here:
http://www.facebook.com/topic.php?ui...27517&topic=97

Relevant reports from the "near misses" section:

"As a SCUBA diver, with no wet suit, approached a moored sail boat he felt a tingling sensation. Approaching closer he experienced a moderate electric shock so he backed away. Later examination disclosed damage to a steel dock section at the boat’s stern and the battery charger was found to have a “short circuit”. The condition of the bonding system was not reported."

"After receiving permission from marina two adult women went swimming near their rented houseboat. As they started back to the boat from the swim slide entry point both felt a strong electric shock sensation, and had the presence of mind to swim away from the boat! A relative entered the water and felt the same thing – which disappeared when the boat was disconnected from shore power. Close call was brushed off by staff so no action was taken to locate source of fault current."

"Seven children swimming behind houseboat received electrical shocks (no fatalities). Lights went out on boat and children immediately started screaming. Cause was loss of neutral, a neutral-ground connection on the air conditioning system and a poor grounding connection on the shore cord."

And from the fatality reports:

"A 14 year old boy died from electric shock while swimming near a houseboat. A friend was also shocked and taken to a hospital and released. A man jumped in to help and was rendered unconscious but was unharmed after regaining consciousness. The cause appeared to be inserting a shore cord with a 30A/125V (L5-30) plug (with the grounding pin bent back) into a 50A-125/250V receptacle in such a way so as to energize the neutral, which was connected to the bonding system, thereby energizing the hull."

"A 16 yr old boy was swimming in the marina when he approached a houseboat. He screamed as if in pain and disappeared under the water. He could not be revived after divers recovered his body. A friend in the water also felt a shocking sensation. The cause was a home made shore cord, hard wired to the panel which was passed through a hole in sheet metal siding with no chafe protection."

"Diver found Aug. 5 in shallow water 8 ft. from his dock, drowned. Incorrectly wired dock junction box caused 117 VAC to appear on metal dock components. Rescue diver reported feeling shock sensation 20 ft. from dock!"

"Young man swimming toward stern of a house boat became disabled and drowned, fresh water. Boat had a neutral-ground bond. Home made shore cord “Y” became partly disconnected causing hull to become energized. 17vac measured behind stern-drive."

"A canoe carrying four young boys tipped over a few dozen yards from a dock. As they swam toward the dock they felt a light tingle. Three of the boys diverted away from the dock while the fourth boy continued into the electric field and drowned. Cause was broken insulation on a dock wire hanging in the water."

So, like it or not, this does happen and it is a real hazard.
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Old 08-29-2011, 04:25 PM   #23
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Is being shocked in a properly bonded pool truly impossible or just improbable?


The bonding test can be done without chopping or cutting an concrete.
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Old 08-29-2011, 04:39 PM   #24
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Is being shocked in a properly bonded pool truly impossible or just improbable?


mpoulton....I have no doubt those all happened.....

But....how many of those people had their feet in the mud at the bottom of the lake?

How many got shocked only when they touched the boat or dock?

I think all of them. In all the cases I'm reading above, there was a path to physical earth ground....I think most of them involved shore power....
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Old 08-29-2011, 07:30 PM   #25
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Have you gotten an electrician on site yet?
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Old 08-31-2011, 11:05 AM   #26
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Is being shocked in a properly bonded pool truly impossible or just improbable?


NJMarine - Could you tell me how? Oh Mike - Not yet. The electrician we used retired. His son was supposed to come out, but didn't. My husband is one of those guys that can fix cars, run plumbing, repair appliances, build things, etc. He has good mechanical comprehension. His problem is reading comprehehnsion. So I am trying to gather the information of what and where to test, etc. No offense, but as you can tell, not all electricians are in agreement about these matters, so not confident they would find the problem any quicker. Nobody is using the pool right now and the issue hasn't reappeared either. To mpoulton and ddawg -I think you are just having an academic debate among yourselves, but in case your replies are supposed to be relevant to the original post, they were in water and touching metal objects and possible concrete when they got shocked.
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Old 09-01-2011, 07:03 AM   #27
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Is being shocked in a properly bonded pool truly impossible or just improbable?


I agree that finding an electrician the is a wizard at trouble shooting might be difficult.

I am only concerned with your liability---not your competence --Just best to cover your butt---

Keep asking your self how will this look in front of a jury?-----Mike----
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Old 09-01-2011, 06:24 PM   #28
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Have you tried bonding the metal ladder to the water,
If there is a potential difference between the ladder and the water,
You can try this by wrapping some wire tightly around the ladder
so that it makes good electrical contact ,
and drop the other end into the pool water.
Now see if this removes the shocks from the ladder.
You can also use a digital volt meter to check for potential
differences between the ladder and pool water.

If the problem lies in a small potential difference between the pool and the ladder this bonding should remove it.
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Old 09-01-2011, 09:35 PM   #29
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Is being shocked in a properly bonded pool truly impossible or just improbable?


You need an ohm meter and a piece of 12 thhn that will reach all the metal parfts in the pool, such as ladders, handrails and wet niche lights housing
I usually use an analog meter. I calibrate with 1 10 ohn and 1 ohm resistor, but in a pinch you could use a digital meter.
At the motor bond terminal attach one end of the wire at each metal point connect the meter between the meter and the metal section. You should get a reading of 0 resistance.
Check from a railing to the metal around the pool it must read 0 ohms. but you can check to see what is not bonded and what is by this method. Touch the ohm meter probes to 2 different metal parts and see what the resistance is between them. Even the wire mesh in the concrete must be bonded. If it's not 0 you have a problem.
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Old 05-27-2013, 10:25 PM   #30
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Is being shocked in a properly bonded pool truly impossible or just improbable?


Actually you most certainly CAN be shocked and I speak from experience where a group of us were shocked and our friend died in front of us because of a malfunction with the underwater lights in an inground pool. What we felt was most definitely more than a tingling, and we were standing in the middle of the shallow end, touching nothing.
I found this site while researching being shocked by pool ladders, as my you g daughter is complaining of being shocked by the ladder at the swim club we belong to...apparently she isn't imagining it.

Quote:
Originally Posted by ddawg16 View Post
Your link is a bit lacking in details...

Bottom line....if the swimmer is not 'touching' anything else in the water, they will NOT be shocked. In order to be shocked, there has to be a voltage across their body. If they are in the water and the water is at a 1000 Vac....their body will also be at that same potential......but as long as they don't touch something...there there is no current flow...and no shock.

In the example you posted...I suspect they touched the boat or their feet touched the lake floor....

Case in point....have you ever seen the guys that work on high voltage lines? They use a helicoptor to drop them right on the line....do they get shocked? No. As they get close, they use a probe to get them and the chopper at the same potential...after that, they climb on.

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