I read an interesting article about potential drownings around docks with p ower connections. Some researchers say the ground connection which goes al l the way back to the power line transformer allows power surges to reach t he dock where it can find its way into the water.
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It seems a bit odd and the drawing shows ground connections at the pole, th e house and at the dock. It's hard to imagine that even without any defect s any sort of voltage would be transferred to the water.
Anyone know much about this?
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Rick C.
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It seems a bit odd and the drawing shows ground connections at the
Evidently not the people who are "researching" it. We would just about all be dead after using 741 opamps on full voltage if they were right.
I quote from their gibberish
}Erler said an electrical current is considered lethal if it's above } 15 Volts rms for 8.3 milliseconds. In the case he presented Thursday } night, he measured a blip of current at 18.7 Volts rms for 40 } milliseconds, far over the lethal amount.
Around 50v rms starts to sting and might actually be dangerous if you were in the water making a good contact with it and unable to escape. See
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If you have a sensitive electrometer you can find truly terrifying voltages between well insulated metal plates at different heights.
No, but it seems intuitively clear that a lake could be a better ground than a copper rod pounded into the soil.
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Phil Hobbs
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Indeed. The only similar instance I can think of is when cattle and racehorses can get electrocuted from the earth by a potential difference arising between their front and back legs when a nearby underground cable sheath breaks. This doesn't affect humans, however, as our feet are normally always too close together.
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Yeah, someone doesn't know what they're talking about:
"Erler said an electrical current is considered lethal if it's above 15 Volts rms for 8.3 milliseconds. In the case he presented Thursday night, he measured a blip of current at 18.7 Volts rms for 40 milliseconds, far over the lethal amount. "
Not exactly confidence inspiring!
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From a utility company engineer, relating to local house flooding issues at a meeting of residents. Apparently fresh-water flooding is worse than sea-water flooding, as a/ sea-water is more likely to trip protection devices and quicker b/ the area of electrified water is much greater for fresh water
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Much lower voltages than that can be unpleasant if you are partly immersed in water. I once had a very painful shock from two series- connected 9V batteries in a hydrophone amplifier when I was standing waist deep in sea water. (I was fitting new batteries to the amplifier which was in a waterproof housing floating above a coral reef. The battery negative was grounded to the seawater through defects in the outer sheath of the shielded cable which was a few hundred metres long and I touched the positive terminal which would have been at about +20Vdc.)
In the old days the standard method to determine why a flashlight did not work, was the bulb dead or the battery empty. Just touch both electrodes of the 4.5 V flashlight battery with your tongue. If you get an unpleasant jolt, the battery was OK, hence the bulb was faulty.
On Saturday, August 10, 2019 at 1:05:39 AM UTC-4, Rick C wrote:
power connections. Some researchers say the ground connection which goes all the way back to the power line transformer allows power surges to reach the dock where it can find its way into the water.
the house and at the dock. It's hard to imagine that even without any defe cts any sort of voltage would be transferred to the water.
Google for "stray voltage". This has been a known problem in some areas for decades. An example is people getting shocks touching metal near pools at their homes. Many times the power companies have investigated and can't even figure out what is wrong, but it appears to be power taking unexpected paths that result in some unintended things becoming energized. The cases I've heard of though have not been fatal or even enough to give a serious shock, more of a tingle. But I can see it potentially being worse in water. In these cases, what they are saying is that by having the equipment grounding conductor at the dock connected to the house the wet area at the lake could be a better ground than the grounding electr ode system at the house. Part of the neutral current from the house will always flow through the ground rod system, back to the utility transformer, instead of over the neutral wire. In this case, the grounded metal of the electric system of the dock, through you, to the water, becomes an alternate path. The rest depends on the relative resistances of the grounding electrode system path at the house and the resistance of the path that you are in. That's why they are proposing that dock systems be separately grounded at the dock, not bonded to the grounding system at the house panel. Even if the grounding electrode system at the house is very good, the total resistance of the path to the transformer depends on the earth in between. If that resistance is high, then more voltage could appear on the alternate path through the metal at the lake, through you and into the water.
But their standard of 15 volts seems very low and while I guess it might be capable of somehow being lethal, I've never heard of a case with voltage that low. 24V is used for all kinds of low voltage systems, eg door bells, HVAC control, etc. I've never heard of anyone being electrocuted from that .
You seem to have gone off half cocked... I have a friend who is knowledgeab le and told me about early firearms. I now know where this expression came from. Half cocked is a safety position in flintlocks where the flint is n o longer near the pan, but the trigger is locked and so not capable of firi ng until the hammer is fully cocked. So going off half cocked means firing for no good reason and potentially causing damage or harm... go figure.
All the data you posted above do not apply when a person is immersed in wat er. Note the title of the article you reference... "Small Contact Voltage Exposures". Small contact is used to specifically exclude situations where the current can enter the skin over larger areas such as when wet or in wa ter.
Then there is this statement by the author...
"Work by Charles F. Dalziel, Richard H. Kaufmann, Edward C. Cantwell, and o thers have shown that it is the volt-amps (VA) energy, or power measured in watt-seconds (W-sec), that ultimately determines if an electrical shock wi ll be lethal"
Maybe you can tell me what is wrong with it? I think such a mistake preclu des believing much the author has to say. Heck, the author doubles down by making the same mistake elsewhere showing it is not a simple typo.
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th power connections. Some researchers say the ground connection which goe s all the way back to the power line transformer allows power surges to rea ch the dock where it can find its way into the water.
, the house and at the dock. It's hard to imagine that even without any de fects any sort of voltage would be transferred to the water.
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Great explanation. I've never actually understood the reason for "groundin g" electrical systems. Everything done by grounding can be accomplished by using a "safety" wire which is essentially a backup neutral. As long as n eutral faults can be detected such as by GFCI, why does connecting to liter al "earth" make a difference?
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Yes, because not many use such devices while up to their necks in water. I believe the voltages referred to in the article are measured across the bo dy, not at the source.
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Rick C.
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"We tested the water in one where there had been a shock and found nothing," Harrington said. "We then put the lift down in the water as it had been described when the shock happened, and the device lit right up."
I don't see how this would happen with a properly wired system. It would seem it has to have a fault. With no fault, the current path would be from the house hot to the dock, through the lift motor, back to the house on the neutral. At that point it's just like any other load in the house, so what's going on at the dock, the metal getting energized, should not depend on that lift motor being energized or not, unless it has a fault. And code has required GFCI at docks for decades now, it would trip in this case and even if it's an old installation, it's easy to add GFCI and you'd be a fool not to.
That from everything we know, including from our own personal experience,
15 volts isn't lethal period, forget about the 8 milliseconds? I suppose maybe you could find someone with some underlying heart problems where if you managed to apply it just right, 15V could be lethal, but I've never heard of such a thing. So, where did these guys come up with that standard? Why is there no number for current?
Safety grounding seeks to put every conductor within reach at the same potential, so that anyone touching two things at once won't be subjected to a potential difference. In most cases, the earth is within reach, so that it too must be connected to the safety ground. Obviously, vehicles do not need to have their safety ground connected to earth, except maybe when stationary and connected to other systems.
The current flowing through electrical appliances should flow from hot to neutral, never to earth. If the earth conductor has a current, that's a fault! The neutral conductor is called that way because at some point, it's connected to ground too, however, since it has a finite resistance and conducts a current, its potential is not necessarily the same as the safety ground.
g," Harrington said. "We then put the lift down in the water as it had been described when the shock happened, and the device lit right up."
I guess that's why people are not shocked at docks. Oh, wait, they are! I f you pay attention to what they wrote they seem to be finding, not the mai n current flowing, but transients that cause voltages to show up on the nor mal routes. The earth ground will have a connection to neutral at the hous e. Any voltage showing up along the resistance of the neutral can show up on the protective earth wire which can lead right to the water.
Yes, clearly this is not an event that happens if you think of conductors a s perfect and grounds as perfect. This is not a problem caused by light bu lbs and coffee pots. The transients in question are short duration but hig h current which then challenge the assumptions we commonly make regarding o ur utilities.
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Does your standard of something higher than 15 volts apply when you are up to your armpits in water? Have you read any of the other posts in this thread where this is explained?
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Rick C.
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