boat lift shocking

[hurk27]

There are other forces that can cause current to flow through the earth. Here is one that can last for hours or days:

In the 1970s scientists at the University of Alaska Fairbanks Geophysical Institute during aurora activity measured ten amperes of direct electrical current generated by the aurora in local power lines. Almost all electrical power lines are built to carry only alternating current. Direct current generated in these lines by the aurora causes heating and other problems in the equipment that is used to distribute alternating electrical power. As aurora occurred Geophysical Institute scientists also measured over 2000 amperes of direct current flowing in the Trans-Alaska Pipeline. This electrical current flows in and out of the pipeline where the pipeline touches the ground which causes increased corrosion or loss of metal from the pipeline at that point. Although the electrical current is large the voltage is only a few thousandths of a volt per kilometer, which is not enough to feel if you touch the pipe.

If I am ever in Alaska I am so not going swimming around that pipeline !!

While the current can flow in Earth, it is because of the solar wind, not the aurora, The aurora is the effect of the solar winds. in the peak of sun spot activity, the aurora can be seen very far south. we have seen it here in Indiana when a large solar flair happens and causes a Geo magnetic storm, Transformers explode and many strange things happen, but even then if you were to take voltage readings from two different points on Earth you would find that these events still didn't cause a difference of potential in earth, it causes a difference of potential between the earth and something influenced by the solar wind, such as the pipe line or the transmission wires. it was a big problem with the telegraph system, back in the early days, this was one of the reasons that an earth reference seemed so important.

 

[jeffhornsby]

Had exact same problem

Had exact same problem

I came across the exact same problem.
The Utlity company drives there ground rod about 50'-100' at the poles in this area of Flordia. The Distance from the Transformer to house was around 750 ft then another 750 ft from house to bay.
Because of The distance between the boat lift and the utility transformer
And the utility rod was driven deep enough to hit the water table.
It was enough to cause a 1to 2.5 volt difference between the salt water and the boat lift connected to the house grounding system

A quick way to test to see if that is problem is to get some scrap #10 connect to the ground bar in the boat lift panel then drop the other end in the water and test your voltage.

I cleared the voltage installing a new sub panel about 40 feet from the bay and driving 30' of rod at sub panel and another 30' of rod near the shore. Then feed the Lift from the new sub panel,

 

[glene77is]

... the primary and secondary EGCs must be bonded to the metal parts of the transformer and these EGCs will be bonded to their respective grounded conductors ...

Don,
Good Point.

 

[glene77is]

Ghost,
Thanks for the article in your post.
I've done reading in Stray Voltage for academic purposes.
The effects are astounding.
With current NESC requirements,
the ground currents will only increase over time.

 

[mivey]

I think if you were to pull the GEC conductors and tested the PoCo neutral to the salt water with the earth not involved you would still have the voltage. Actually, the voltage may go up.

If you pulled all of the POCO grounds, yes. I doubt the local ground much impact at all as the local ground is not going to "pull down" the neutral voltage.

 

[mivey]

There is no substantial ground current.

This means that ITC, that now owns these lines, has good neutral conductor connections on the towers.

Maybe, but I think it points more to the lines being closely balanced. If it were single phase lines, I might agree, depending on the system size and loading data.

In any locations I have checked I have not found substantial voltage gradients in the earth.

I'm guessing you don't have a lot of neutral current on the primary distribution. Try to find a long single phase distribution line. Might be something I could do in the next week or so.

 

[mivey]

Don,

The primary and secondary are isolated
by a capacitance shield which is grounded.
No stray voltage leaking across the Prim/Seco core.

On the Secondary load circuit, the only reference is the other leg from the transformer secondary.

Thus, the POCO reference is out of the picture.

This was the typical approach used in hospital ICU applications, where patients are connected intra-venously and are 10 times more sensitive to leakage currents than the standards used for GFCI applications. We tested at 10 microamp increments on our scale.

Comments are welcome.

Are one of you talking about an isolation transformer and the other a neutral isolator?

 

[mivey]

The problem here is we are dealing with water, it doesn't require very much voltage to cause a problem where the human body is in immersed in water, touching something that is just 1 or 2 volts above Earth. we don't hear of all the other times because it doesn't involve the above. so it goes unnoticed.

I agree. But what I was wondering is if the voltage is often well above 1 or 2 volts.

now as far as the voltage drop problem on power lines using only one of the three phases, remember there is very little current on most power lines

Don't think I'm agreeing with you here. We often have a lot more current than that on our lines.

, 6 or 7 amps at 7200 volts will give you 180 to 210 amps at 240 volts, so if a line only has one or two houses on it, the current on the MGN will be very little, so in most cases the 4 rods per mile do there job and keep the voltage drop on the MGN down to practically nothing. so this is why stray voltage is kind of rare to be a problem, but it does happen.

Don't buy that either. The basic model is that the neutral current leaves the pole and heads toward and away from the direction of the source. It starts dividing a small amount into the earth as it hits each grounding point at the next pole. While the earth has practically zero resistance, our connection to it does not and the earth is only going to share so much of this current.

Actually the highest resistance is found the closest to the connection point of earth, this is because of the small amount of earth around this connection point, as you get further out from this connection point the resistance of earth gets lower because of the greater amount of earth or parallel paths...

agree

It doesn't work this way, the reason is because current takes all paths back to the source, when we start thinking about the paths in earth or a large body of water we must start thinking in three dimensions, not two, and because almost all the voltage will be dropped in the first 26' from the contact point to earth or about 19' in salt water, and as high as 40' in fresh water, after these distances from the connection point to earth/water it can be said the resistance of the rest of the pathway is 0 ohms. now if it is at 0 ohms then the current will take all pathways equal in all directions back to the source, even around the whole globe and even through the earth.
again see the link I posted to hardworkingstiff. about Gary's experiments.

Yeah, I get that. Maybe it is the level of currents involved. At some proximity and some level of current the ground gradient becomes significant.

It would be nice to have Meliopoulos's model that was mentioned in the video. I do have his grounding book at home and I'll have to see if his model is in there.

I have been thinking about making a model to play with. I'm thinking about a 1-2 ohm ground connection at the sub and 25 ohm at the poles. I would include variables for these connections as well as some series impedances for poor splice modeling. I was also thinking using a short transmission line model between each pole would be accurate enough.

 

[mivey]

091022-2308 EST

don:

My home pole transformer is an isolation transformer. Primary side has no neutral, only two posts fed from an essentially delta system. This is not covered by NEC. Lots of these delta systems exist in our area. It may be a Y source at the substation, but from my view point it is three wires only and thus to me looks like a delta.

.

Your primary distribution is delta with no neutral or are you saying you have a two-bushing transformer? I think you may have posted pictures but I'm too lazy to look for them now.

As you know, if the POCO is using two-bushing transformers they are just reducing the neutral current and vdrop.

If they have a neutral, I supsect there is still some neutral voltage, even though it will be much smaller than a system using single-bushing transformers.

 

[mivey]

I came across the exact same problem.
The Utlity company drives there ground rod about 50'-100' at the poles in this area of Flordia. The Distance from the Transformer to house was around 750 ft then another 750 ft from house to bay.
Because of The distance between the boat lift and the utility transformer
And the utility rod was driven deep enough to hit the water table.
It was enough to cause a 1to 2.5 volt difference between the salt water and the boat lift connected to the house grounding system

A quick way to test to see if that is problem is to get some scrap #10 connect to the ground bar in the boat lift panel then drop the other end in the water and test your voltage.

I cleared the voltage installing a new sub panel about 40 feet from the bay and driving 30' of rod at sub panel and another 30' of rod near the shore. Then feed the Lift from the new sub panel,

I missed something. Are you talking about the solar wind currents or the primary neutral with an elevated potential?

 

[mivey]

While there are some rare installations where the code does permit the installation of a truly isolated device, this is not one of them. In most cases, the code rules prohibit true isolation as both the primary and secondary EGCs must be bonded to the metal parts of the transformer and these EGCs will be bonded to their respective grounded conductors so there is no real isolation between the primary and secondary grounded conductors.

And I'm not so sure I trust those neutral isolation devices to re-connect when they are supposed to. Are these things routinely tested or do they just sit out there forever waiting for an event? I guess I need to read up on these devices.

 

[gar]

091023-1139 EST

mivey:

For my home location I have no idea what is at the substation. However, to my neighborhood there is only a three wire primary with no neutral. My transformer is a two bushing primary. The only connection to ground at the pole is from the secondary neutral. This transformer has been in operation since late 1965.

The photos are at:
P4 is transformer primary.
P5 is three primary wires to other customers further from the substation.
www.beta-a2.com/misc_TMP_photos.html

At the shop location I mentioned above in this thread the primary supply is a 4 wire Y. Two phase wires and neutral from this primary, therefore 3 wires, feed the two primaries of the two transformers. The secondaries are connected open delta. The single phase transformer of this pair is 100 KVA, and the other has no label and is about 50 KVA. It is important to note that the ground voltage vectors tend to point toward the substation and other primary grounding points.

To repeat these vectors were:
N 21 MV
NE 44 MV
E 132 MV
SE 109 MV
S 167 MV
SW 109 MV the direction of the substation
W 80 MV
NW 48 MV

The center of these measurements was the pole ground rod.



If a Y distribution system supplies a two bushing transformer and there is no external connection of the primary neutral to the secondary neutral, then this is an isolation transformer. If the primary neutral is not grounded at the pole with the transformer, but one or more poles away from the transformer, and the secondary of the pole transformer is grounded at the transformer pole, then there should be little effect on ground voltage difference from the pole transformer ground point to the main panel ground point other than the voltage drop on the neutral from the transformer to the main panel.

.

 

[mivey]

The photos are at...

Thanks. For some reason your specific primary setup did not stick in my brain.

If a Y distribution system supplies a two bushing transformer and there is no external connection of the primary neutral to the secondary neutral, then this is an isolation transformer. If the primary neutral is not grounded at the pole with the transformer, but one or more poles away from the transformer, and the secondary of the pole transformer is grounded at the transformer pole, then there should be little effect on ground voltage difference from the pole transformer ground point to the main panel ground point other than the voltage drop on the neutral from the transformer to the main panel.

Agreed. In this case you have isolated the secondary neutral from the primary neutral. The 3 volt primary neutral, even though it is sitting on the pole, has no connection at the transformer pole.

That said, I can't imagine the POCO would not ground the neutral at the transformer pole. They might ground it through one of those neutral isolation devices (I still have not read up on those).

You have described the neutral isolation device scenario except with the device disconnected. And your scenario wouldn't stick/fail in the closed position (but is permanently "stuck" in the open position).

 

[wirenut1980]

And I'm not so sure I trust those neutral isolation devices to re-connect when they are supposed to. Are these things routinely tested or do they just sit out there forever waiting for an event? I guess I need to read up on these devices.

We inspect our neutral isolators annually. I agree with many that the issue is the dock has 1.3 V on it with respect to the water. The 1.3 V is the primary utility neutral voltage drop. With only 1.3 V, I doubt there are any bad connections on the primary neutral, but it wouldn't hurt for the utility to check. A neutral isolator is the solution as many have said.

 

[hurk27]

091023-1139 EST

mivey:

For my home location I have no idea what is at the substation. However, to my neighborhood there is only a three wire primary with no neutral. My transformer is a two bushing primary. The only connection to ground at the pole is from the secondary neutral. This transformer has been in operation since late 1965.

The photos are at:
P4 is transformer primary.
P5 is three primary wires to other customers further from the substation.
www.beta-a2.com/misc_TMP_photos.html

All I can say is WOW!, I have never seen just phase conductors running down poles with no MGN?

I'll bet your power company plays heck with lightning strikes to the phase conductors, and Geo-magnetic storm's cause problems in your area, with no MGN to drain static voltage off.
Those lines to Earth reference will be all over the place.
here all poles have an MGN running down them, its the bottom line.
In Florida it's the top line, and it's the highest because of the lightning down there, it acts like an interceptor line such like Ufer would place running above explosive storage areas.

I just never seen none at all?

Guess that is why I was so confused in other threads when you mentioned this.

we have two bushing transformers for single phase loads but they are rare. and even then there is still a MGN on the pole, it will have single bushing transformers on it from transformers down the road, so there can still be voltage drop on the MGN which every secondary X0 is bonded to.

I'll try to get out and take some photo's this week end if the weather clears up.

 

[gar]

091023-1751 EST

hurk27:

I can drive all around our area and find many areas with primaries like mine. I suspect the substations have Ys and the only ground would be there. And yes there are many that have MGN systems. I can go 1/2 mile from my house and find a Y system feeding single bushing transformers. Also we have a lot of open delta secondaries.

Most problems here are trees. And they fall across the lines bringing them down.

.

 

[SG-1]

While the current can flow in Earth, it is because of the solar wind, not the aurora, The aurora is the effect of the solar winds. in the peak of sun spot activity, the aurora can be seen very far south. we have seen it here in Indiana when a large solar flair happens and causes a Geo magnetic storm, Transformers explode and many strange things happen, but even then if you were to take voltage readings from two different points on Earth you would find that these events still didn't cause a difference of potential in earth, it causes a difference of potential between the earth and something influenced by the solar wind, such as the pipe line or the transmission wires. it was a big problem with the telegraph system, back in the early days, this was one of the reasons that an earth reference seemed so important.

I agree the current is caused by the solar wind buffeting the earth's geomagnetic field. The aurora is a beautiful product of that. I was in contact with a man that has ground rods set up to alert him of aurora activity. I seem to remember that a few milliVolts were measured between rods a hundred meters apart. He lives at a very high latitude.

 

[mivey]

it can be said the resistance of the rest of the pathway is 0 ohms. now if it is at 0 ohms then the current will take all pathways equal in all directions back to the source, even around the whole globe and even through the earth.
again see the link I posted to hardworkingstiff. about Gary's experiments.

FWIW, while it might be fun to say this for illustrative purposes, it is an exaggeration. The earth resistance is not really zero and the current will not evenly disperse and travel around the globe and through the earth (I guess unless the source and load are on opposite sides of the earth).

 

[wirenut1980]

All I can say is WOW!, I have never seen just phase conductors running down poles with no MGN?

I'll bet your power company plays heck with lightning strikes to the phase conductors, and Geo-magnetic storm's cause problems in your area, with no MGN to drain static voltage off.
Those lines to Earth reference will be all over the place.
here all poles have an MGN running down them, its the bottom line.
In Florida it's the top line, and it's the highest because of the lightning down there, it acts like an interceptor line such like Ufer would place running above explosive storage areas.

I just never seen none at all?

Guess that is why I was so confused in other threads when you mentioned this.

we have two bushing transformers for single phase loads but they are rare. and even then there is still a MGN on the pole, it will have single bushing transformers on it from transformers down the road, so there can still be voltage drop on the MGN which every secondary X0 is bonded to.

I'll try to get out and take some photo's this week end if the weather clears up.

I have dealt with these systems before while working for a utility in Missouri. Gar is correct, the system is a delta with no MGN.

The only systems I have seen are old and in rural areas, with voltages either 2.4 kV or 4.16 kV in small towns. These systems are getting fewer and farther between.

 

[gar]

091025-0935 EST

jeffhornsby:

In reference to your post #42.

Is this your home? If not, then is it close? Would the homeowner be willing to let you do some voltage measurements?

What does

The Utlity company drives there ground rod about 50'-100' at the poles in this area of Flordia.

mean? Are the ground rods 50 to 100 ft long and driven vertically into the ground? Or are the rods 8 ft long and the spacing of rods is 50 to 100 ft? The later would mean the water table is close to the earth's surface.

If you were to get a long wire, connect this wire to the ground rod at the transformer pole, use the wire as one test lead to a high impedance voltmeter (millivolt as well), then what are the voltages to a screwdriver probe as you follow a path from the pole to the water staying somewhat away from the ground rods at the house and those you put near the water?

If your theory is correct that the power company ground rod at the pole transformer is creating a low impedance path out to the salt water, then these probe voltage measurements relative to the pole ground rod should be quite small, maybe 100 MV or less. My 100 millivolts criteria is sort of arbitrary at this time.

Before you drove your ground rods at the dock area the voltage difference from the water to the EGC at the dock was 1 to 2.5 V. If all load at the house and the dock was disconnected, then did this voltage difference drop to zero? If it did not drop to zero or near zero, then there was not a low impedance path from the transformer pole ground rod to the sea water. By removing all load there is no current in the neutral from the house to the pole from loads of the house and beyond, and therefore no voltage drop from load current. There may, and probably is, current in the neutral from power system neutral current flowing to the ground rod at the house main panel. This is probably not large enough to produce much drop on the transformer to house neutral.

More experiments and information from you could be very useful.

.