Power Line Grounds Near Water

I think you're missing my point here. I'm assuming the issue here is with the copywriter rather than the scientists. I have to assume the scientists know the difference between current and volts!

Here's the quote: "Erler said an electrical current is considered lethal if it's above 15 Volts rms for 8.3 milliseconds."

You do realise 15V rms is not a measure of current, right?

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IMBALANCE! I think at least half your problem is not so much with the science, but with phraseology and plain English comprehension.

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thing," 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."

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! If you pay attention to what they wrote they seem to be finding, not the main current flowing, but transients that cause voltages to show up on the normal routes. The earth ground will have a connection to neutral at the house. 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.

rs as perfect and grounds as perfect. This is not a problem caused by ligh t bulbs and coffee pots.

Did you read any of the article? Do you not understand (which they clearly indicated) that startup transients of motors and such are much larger than the static currents of coffee pots?

cal

I don't know about pools. I don't see how there would be current through t he water in a pool. The pool is electrically isolated within the pool conf inement. Where would the two electrodes be? The concrete is sealed, so cu rrent doesn't go through that.

n challenge the assumptions we commonly make regarding our utilities.

What assumptions would those be?

Yeah, what's your point? They evaluated existing installations and also in stallations which were then brought up to code. They said the upgraded ins tallations were actually worse. I'm not sure what code changes were requir ed.

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Rick C

WTF is a "static current"??

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s,

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cle talked about "with the lift in the water", not energized. The metallic cables of the lift conducted the ground circuit to the water.

it, but

d hot wires. I don't follow what you are saying about cutting the ground w ire. Where do you cut it? I believe this no longer adheres to code no mat ter what... unless you are talking about providing a separate ground rod fo r the dock.

What he's saying is to use a GFCI on the dock circuit, which has been required in code for decades and to cut the ground wire that runs to the house panel. The GFCI will protect if there is any f ault by detecting the current imbalance. I would also install at least one good ground rod at the dock and bond that to the electric grounds there instead of having it tied to the house ground system. Of course that is not code compliant, but it appears better to me than the alternative and if you include the new ground rod at the dock, it's what the guys in that article are trying to get implemented.

Of course we haven't heard the other side of the story, ie why the NEC folks don't appear to buy into it, what their concerns are. In issues like this, there frequently isn't an ideal solution, you're frequently having to trade off one potential problem for another, but reducing the chances of getting a shock, you would think would override most other concerns.

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Whoey Louie

I realize the dangerous current happens when the voltage is above 15 volts.

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and hot wires. I don't follow what you are saying about cutting the ground wire. Where do you cut it? I believe this no longer adheres to code no m atter what... unless you are talking about providing a separate ground rod for the dock.

fault

The sources of the transients are not actually known. It may be that there are issues with grounding at the source and there are transients on both t he hot and neutral lines. A GFCI won't prevent common mode currents from f lowing in both sides of the power line.

From the article the NEC guys just don't want to hear about it. I get that . I expect they hear from any number of individuals with suggestions. If these guys get enough attention from the Virginia legislature maybe the NEC will pick up the ball and run with it. Maybe these guys are wrong about s ome aspects of the problem. But *something* kills people in the water arou nd docks and these guys have measured dangerous voltages which should be in vestigated.

I have read reports of this before including people who died trying to save others. The news reports are not investigations and the assumption is alw ays that there is something wrong with the wiring.

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l and hot wires. I don't follow what you are saying about cutting the grou nd wire. Where do you cut it? I believe this no longer adheres to code no matter what... unless you are talking about providing a separate ground ro d for the dock.

ny fault

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I noted that and that there was no indication that any attempt was made to find the source.

I specifically noted that when I said there is no indication they even examined the grounding electrode system or took any measurements there.

prevent common mode currents from flowing in both sides of the power line.

Nor will it prevent a large static neutral current from generating a voltage capable of shocking at the dock.

I find that hard to believe, as they are updating the code every year and from all that I see, they are very concerned about safety, so I would think they looked into the merits of this. What their position is, we don't know.

stions.

It's not the numbers, it's what the issue they have identified is, whether it;s legitimate and if there is a solution that makes overall safety better. It could be that despite all the measuring, there are few or no cases of people being injured or dead due to this. Isn't it a bit curious that in that article there are no examples, no cites of actual numbers?

If these guys get enough attention from the Virginia legislature maybe the NEC will pick up the ball and run with it. Maybe these guys are wrong abo ut some aspects of the problem. But *something* kills people in the water around docks and these guys have measured dangerous voltages which should b e investigated.

ve others. The news reports are not investigations and the assumption is a lways that there is something wrong with the wiring.

It's almost never an assumption, these fatalities are investigated and the cause usually determined. And in all the lethal shocks that I've seen reported, there has been a fault.

Reply to
Whoey Louie

This is a recognised configuration in UK wiring regulations, and is called a TT system in IEC terminology.

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The US is still using technology considered modern in 1876 as usual.

Reply to
Wolf Bagger

OK, fine. But when I'm reading through an article like that and come across such sloppy writing it really shakes my faith in the veracity of the entire contents and I generally don't bother reading any further. This is something that would never happen fifty or sixty years ago, which is why I prefer text books from the 1930s and 1940s. The clarity and precision of language back then was immeasurably better than what we find today. And it's really no surprise when there are so many writers around nowadays who learned English in the kind of school Bill Sloman would approve of.

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ny fault

o

From your cite:

"TT networkEdit

In a TT (terre-terre) earthing system, the protective earth connection for the consumer is provided by a local earth electrode, (sometimes referred to as the Terra-Firma connection) and there is another independently installe d at the generator. There is no 'earth wire' between the two. "

That exactly describes the system in place in the article, that's showing potentially dangerous voltage at the dock. It's what I have here, it's exactly what just about all homes have in the US. They have a grounding electrode system at the disconnect at the house, there is no ground wire back to the generator. Was there ever? Hello?

Reply to
Whoey Louie

Really? This is a local TV station article, not one published in the IEEE. Actually for something written by a TV reporter, I'd say it's excellent, much better than 99% of the ones I've seen over the ages.

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Whoey Louie

ny fault

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Lol! Yes, I am very familiar with TT installations. They were done to sav e a single conductor in the local power line. I am told they are deprecate d in the UK and most modern installations have the TN-S like the US. Not s ure if that is true. I'm also told many TN-S installations are converted t o TT when the foil used for the earth connections corrodes and not replaced . Then a local ground must be installed and bonded to all earth wires in t he house. I'd rather see them fix the wire.

I'm glad the US uses TN-S. It is the safest of any of the conventions. I think you must be confusing this with something else.

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ny fault

o

Lol! Yes, I am very familiar with TT installations. They were done to sav e a single conductor in the local power line. I am told they are deprecate d in the UK and most modern installations have the TN-S like the US. Not s ure if that is true. I'm also told many TN-S installations are converted t o TT when the foil used for the earth connections corrodes and not replaced . Then a local ground must be installed and bonded to all earth wires in t he house. I'd rather see them fix the wire.

I'm glad the US uses TN-S. It is the safest of any of the conventions. I think you must be confusing this with something else.

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Rick C

any fault

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r the consumer is provided by a local earth electrode, (sometimes referred to as the Terra-Firma connection) and there is another independently instal led at the generator. There is no 'earth wire' between the two. "

You should learn about things before you post. There is no galvanic connec tion to the generator, so it would not matter if it was grounded or not. T he galvanic connection is from the transformer which IS grounded and an ear th wire is provided to the house. There can be another ground at the house , but that is usually to the water or gas line coming in from underground r ather than a separate ground rod connection like they use in a TT system wh ere the ground connection must be below some resistance. One of the proble ms with a TT system is poor soil not providing a good enough ground connect ion.

Hello?

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Oh, a TV reporter? In that case it's an amazingly accurate, beautifully- crafted piece of journalistic excellence!

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for the consumer is provided by a local earth electrode, (sometimes referre d to as the Terra-Firma connection) and there is another independently inst alled at the generator. There is no 'earth wire' between the two. "

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ection to the generator,

Maybe you should learn terms before you use them. Galvanic ISOLATION is used to avoid corrosion with dissimilar metals, it has nothing whatever to do with earthing of electrical systems, the term is never used. If you're claiming that generators at the power plant are not earthed, I'd like to see some references for that.

More to the point, you have an incredible ability to take something relatively simple and go off into the wilderness, now you're talking about generators, when the dock issue has absolutely nothing to do with generators. It's a simple multi-path earth ground problem. And that house system with dock is earthed at the main disconnect, just like the example of that TT system, that was presented as some European better idea. Capiche?

is from the transformer which IS grounded and an earth wire is provided to the house.

Maybe you should read before you post? NEC says nothing about "galvanic" anything at the panel or at the transformer. And it's wrong too. The transformer is earthed at the street and the house system ground system is earthed at the main disconnect. At both the transformer end and at the house main disconnect end they are bonded to the neutral.

er or gas line coming in from underground rather than a separate ground rod connection like they use in a TT system where the ground connection must b e below some resistance.

More BS. It's required by code that the service be earthed at the main disconnect, there is no option. It's been like that practically forever. And if a metal underground water line is present, it *must* be part of the grounding electrode system. Other permissible ground electrodes include ground rods, Ufers, ground rings, ground plates, etc... One or more of those can be used as the grounding electrode system. Of course we don't know what was used, or if it's even connected correctly in the example from that article, because they showed no interest in anything at the house panel, which is quite remarkable.

ough ground connection.

Yes, hello indeed. That's a potential problem with just about any earthing system. What was the resistance of the grounding electrodes at the system in the dock example? What was used? We don't know, because apparently they didn't bother to check any of that. Maybe that's part of why the NEC folks didn't pay much attention to them?

Reply to
Whoey Louie

any fault

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ave a single conductor in the local power line.

Wrong again. Look at the diagram shown in his link of the TT installation, It shows 3-phase Wye to a consumer, with neutral. The earth is not used to transfer power. What you are talking about now is a single wire earth return, even further off into the wilderness.

I am told they are deprecated in the UK and most modern installations have the TN-S like the US. Not sure if that is true. I'm also told many TN-S installations are converted to TT when the foil used for the earth connecti ons corrodes and not replaced. Then a local ground must be installed and b onded to all earth wires in the house. I'd rather see them fix the wire.

I think you must be confusing this with something else.

Now you're telling us what is safer, when you started this by not being able to understand how there was stray voltage at the dock? And BTW, even the title of the thread is wrong. That article you cited is not about "power lines near docks". There is no power line near the dock. It's about voltages from unintended ground current from the equipment grounding conductor at a dock.

And those diagrams of the power systems are incomplete and misleading. They show a "consumer" and then talk about power being delivered to devices. WTF does any of that mean? Is the consumer boundary at the house panel or the toaster? It's important because in the US there is a huge difference. The US has no separate ground wire between generator or transformer and your house. It's a neutral earthed at the transformer and at the main disconnect at the house. From there into the house, it's a separate neutral and ground. None of those diagrams show that, none show the required earthing at the house, which has been part of code forever. It's wrong, very wrong.

Reply to
Whoey Louie

On 2019-08-11 13:32, Rick C wrote:>

This is what the UK almost universally uses for the primary supply as well (where it was traditionally known as PME - "protective multiple earthing"), with the exception of rural locations which might be supplied by a pole transformer instead of a substation with substantial earthing provision.

TT is still indicated for external locations removed from the primary location where a supply is terminated such as sheds, garages, poolhouses, docks, etc. to deal with problems caused by conductor resistance.

Reply to
Wolf Bagger

I'm pretty sure PME uses a single conductor for earth and neutral from the transformer to the premises. TN-S uses a separate conductors for earth and neutral.

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