Ground Loops

[JohnRodriguez]

Chuck the reason you get shocked in this situation, is that with the neutral tied to the frame, the only path to ground was tru the water, and when a body touched the dock, you became a better conductor than the water, hence the current/shock going tru youl, back to the water on to ground. That's why you don't tie the neutral to anything. one other bad thing about sharing 1 neutral between 2 hots on different phases (this is a common thing in house wiring, it save money and time to run 12-3 piece of romex wire around a living room) if you lift the neutral or lose the neutral some how, you will put 240 volts on your tv set, stereo, etc, and they don't like that.

I guess this is a EE gathering discussion, sort off. I left NMSU in 95 with 18 hours left to get my EE in digital microelectonics. got burned out so I figured i'd go work construction again for a couple of year, somehow ended up as a mine electrician and haven't been able to get away form the sunshine and clean air (after they shut down our smelter) and pay. Now i'm to onery to put up with a professor, especially some of the jerks I had 10 years ago. On the plus not I attended a class a couple of years ago for power generation and distriution for our power house (gas boilers and gas turbine units) the instuctor was from Cadick corporation and the instructor explained in two days what I was supposed to have learn in EE214 and 314 (power systems) This guy was a power grid operator in NY for 35 years and now he certifies all the system operator in the nation, something to be said for on the job learning

GG you might try a sheet of SS plate about a 10 guage, our SX/EX (giant 4160 battery) uses them and they seem to work pretty good. The limestone might be acidic enough to keep alge from growing.

[Gun Geek]

Chuck the reason you get shocked in this situation, is that with the neutral tied to the frame, the only path to ground was tru the water, and when a body touched the dock, you became a better conductor than the water, hence the current/shock going tru youl, back to the water on to ground.  That's why you don't tie the neutral to anything.  one other bad thing about sharing 1 neutral between 2 hots on different phases (this is a common thing in house wiring, it save money and time to run 12-3 piece of romex wire around a living room)  if you lift the neutral or lose the neutral some how, you will put 240 volts on your tv set, stereo, etc, and they don't like that.

I guess this is a EE gathering discussion, sort off.  I left NMSU in 95 with 18 hours left to get my EE in digital microelectonics.  got burned out so I figured i'd go work construction again for a couple of year, somehow ended up as a mine electrician and haven't been able to get away form the sunshine and clean air (after they shut down our smelter) and pay.  Now i'm to onery to put up with a professor, especially some of the jerks I had 10 years ago.  On the plus not I attended a class a couple of years ago for power generation and distriution for our power house (gas boilers and gas turbine units)  the instuctor was from Cadick corporation and the instructor explained in two days what I was supposed to have learn in EE214 and 314 (power systems)  This guy was a power grid operator in NY for 35 years and now he certifies all the system operator in the nation, something to be said for on the job learning

GG you might try a sheet of SS plate about a 10 guage, our SX/EX (giant 4160 battery) uses them and they seem to work pretty good.  The limestone might be acidic enough to keep alge from growing.

<{POST_SNAPBACK}>

Just to be clear: the neutral is NOT tied to the frame, the ground wire is tied to the frame (which is exactly what most electricians will tell you to do). You still get shocked if the power is turned off. The shock is not associated with the AC power. It is associated with 2 points on the earth ground being at a different potential.

That's why this is an interesting problem - you do stuff like you are supposed to do and it produces a shock.

Set it up against code (electrically float the dock by isolating it from from the neutral and the phase) and there is no shock - though it will likely be be unsafe if there is a problem.

[George]

You do not get a shock if you disconnect both the neutral and the ground wire (did this only with the phases off) Re-connect the either the neutral or ground and the shock comes back

Game over here. Others are saying the same and now that a new data point is on the playing field, the issue is solved, you just have to trace the fault.

- The lake is not charged.

- The ground potential here, or there is no issue.

Bottom line, current is flowing on YOUR EXISTING service ground and you need to find the fault, not re-engineer the dock service tie away from the established construction practices outlined earlier.

The Neutral is either improperly bonded to the service ground between the utility and you, or it is open and the ground is actually doing the return job to the utility transformer and you have a real big loop going!

There is absolutely no way this happens if they are not improperly bonded upstream, or work is forced to return to Neutral through ground (this is an open neutral).

Once you fix this problem, just ground the entire metal assemblage at the water back to the main service box (not the ground stake) and then let the main service box tie to the ground stake be the ONLY tie to actual ground and make sure it is a REAL good one. Use wire of at least #4, or larger for the hots (I am just guessing that the service breakers are 30 amp at max) if the run is more than 150 feet and the current draw is anywhere near the max of the service breakers (75% breaker rating is max constant draw and considered a fully loaded circuit). I like to see a ground be as heavy as possible a gauge of wire. Johns specification of 4-ought is not an outrageous one.

BTW, if you get a lot of Lightning in the area, all bets are off! ;-)

--

Regards,

Edited July 12, 2005 by George

[George]

One more thought.

It doesn't take much more than a single abraded neutral in a grounded conduit somewhere to bond them enough to flow a current out to the lake on either low wire (G/N). So it might not be the utility after all. This type of thing can be tough to trace and usually requires a one by one disconnect of every wire in the service box in a round robin elimination contest.

If you can get a clamp-on ampmeter and check the ground wire for current flow and whether there is any current flow in the incoming neutral at all you might get an idea.

If you shut off your incoming breakers at the utility entrance to your property and then disconnect the neutral there for a test, you should now be able to hook up the dock to the house/service ground and have the neutral and hots connected out to the dock without any shocks happening.

If you get shocks with "cold" wire connected from house service box to dock, then you need a research team out there right away ;-)

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Regards,

Edited July 12, 2005 by George

[Gun Geek]

Did a quickie of a picture (10 minutes).

George does this fit with your understanding?

Shock occurs if G is connected, power on or power off

It does not occur if G is disconnected, power on or power off.

[George]

Neutral and Ground are NOT supposed to be grounded/connected together after the service transformer where the voltage is stepped down to 208/220. If you disconnect the incoming neutral from your service, this should stop the shocks from happening with all wires hooked up to the dock AND the hot utility service breakers OFF.

If the neutral and the service ground are mechanically bonded anywhere past the step down transformer, but ahead of the service box entrance, you have a problem that needs fixin'. Same thing if you have bonded it in the box (I have seen folks use the ground buss bar for the neutral and vice versa).

--

Regards,

Edited July 12, 2005 by George

[EricW]

Geo,

I love ya, but I have to disagree. Ground is not ground is not ground. It's REALLY common to have differing ground potentials even over a short distance. It's a major problem in factories. It's such a problem that industrial machine manufacturers have on board transformers that create their own, isolated ground so their electronics don't freak out.

I have absolutely no problem believing that there is a difference in ground potentials between a house and a nearby body of water. Especially with that kind of geology.

I'm not saying it's impossible for the neutral of the step-down transformer to be floating, but it's pretty unlikely and it would be the last thing I would look at. The electrical utility is also the last entity you want to get involved since it's almost certain that the dock was wired without a permit (among other things) which could run into beacoup bucks if the gubmint gets wind of it.

[EricW]

The only other thing I can think of would be to go to Home Depot and rent an industrial (read: Gigantic) hammer drill and drill a hole for a ground rod deep into the limestone near the dock. Then bond the ground rod into the rock with a conductive epoxy. I have no clue if that would give enough conductivity, but it's the only other thing I can think of besides grounding the dock to the H2O.

[George]

He states he is only getting the shocks when either the ground wire, or the neutral are hooked up. This says that they are one and the same. They should be close in potential, but they should not be one and the same electrically even though work will happen from hot to neutral, or ground. The neutral is grounded somewhere, or open and the current is flowing through ground to his ground point making his ground wire a somewhat resistive neutral ;-)

We use ISO transformers all the time in my biz (portable video and projection). We dump the incoming neutral, pass the ground through and regenerate the hots through the transformer. The transformer then gives us a brand new neutral from the low side of the transformer windings without any crap on it and at exactly ground potential if the loads on the phases are equal. This eliminates problems with other systems and utility faults putting stray currents on our neutral on us. Ground is ground, but neutral is not always ground and sometimes gets itself tangled up with it's 0 volt sibling in a current flow debacle of some magnitude ;-)

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Regards,

[EricW]

Geo,

He states he is only getting the shocks when either the ground wire, or the neutral are hooked up.

Exactly.

The voltage creating the shocks is between the ground potential that is the H20 and the ground potential that is the stake in the ground at his electrical service box. It's common phenomena. All grounds are not necessarily equipotential.

Remove the ground wire from the dock and you've effectively disconnected the battery.

[Gun Geek]

Just to be sure I've conveyed this right:

When the N was connected to the dock frame, shock occured, power on or power off.

A ground wire was added - it connects directly to the ground rod. The N is NOT now connected to the frame. The G is connected to the frame.

Shock occurs with the G connected to the frame power on or power off.

The G & N are connected (bonded in the vernacular) - in this case at the meter where the service enters the house. After that they do not touch. In the main breaker box of the house, they are at the same potential (0v on a meter) and 0 ohms resistance when measured with a meter. Check out these diagrams - they are not my work (this upload stuff is cool).

[George]

Here is a much more correct diagram showing how power really is distributed and wired for both industry and household usage. Note the N-G bond occurs at the XFMR, I shudder when I see this bonded in service boxes, or right to the cold water/earth ground point the service box connects to. Nooooooooo! Always let theutility do that at the pole! Get your service ground from the ground, or a cold water pipe right at your service entry point. Don't re-bond the neutral to it, sheeeesh!

[Gun Geek]

Here is a much more correct diagram showing how power really is distributed and wired for both industry and household usage. Note the N-G bond occurs at the XFMR, I shudder when I see this bonded in service boxes, or right to the cold water/earth ground point the service box connects to. Nooooooooo! Always do it at the pole!

<{POST_SNAPBACK}>

George:

I think grounding at the service is common practice - maybe even recommended practice. Check the graphic below, the source is: http://www.enm.com/training/siemenscourses/load_2.pdf. This is exactly how my dock is now wired. Where they have a "Downstream Loadcenter" is the loadcenter on the dock. They show it bonded to the enclosure and to an enclosure around a load - the frame of the dock.

[George]

Also to remember, if the ground and neutral really were the same thing, you would only need one of them. You really do need both and they really do have to be separate paths right to the utility xfmr. Every single UL rated metal boxed electrically powered product made has the metal shell attached to ground. Not a single one has the Neutral connected to the chassis box!

--

Regards,

[Too_Slow]

George,

In my area it is code that you have to have a ground rod at the meter and you also tie to the cold water pipes inside for home wiring. It is a little bit different for industry though.

[George]

Maybe yes common in homes, but only for single phase. Definitely not safe in a 3 phase (delta) system where the neutral can carry significant current when the loads are unbalanced (they are never really balanced).

I increased the quality of my ground point at my home (semi-urban area) by re-bonding the can with a piece of #2 welding cable right to where the cold water pipe enters from underground to the street and removed the jumper that was connecting the neutral bar with the service can. All my phone lines got a lot quieter (they are grounded with my AC system) and I get less bips and hits in audio and video recordings now.

Try removing the neutral/ground strap in your service can and seeing if a voltage potential develops between them under load. If it's big (5-10 volts, or more) leave them bonded for safety's sake and think about re-thinking your ground scheme, or seeing if the utilities neutral really is the whole 115 (or whatever) volts away from the hot that the ground is. If it's a small (.5-1 volt) difference with the neutral un-bonded, leave it float and try the dock setup again.

It would be interesting to see what voltage a piece of wire long enough to make it to the lake from a hot breaker in your service box would show referenced to the ground point without the neutral bonded to it. Then take that same hot wire to the lake and try it against the dock just as it is to see what voltage exists from it to the dock. This will tell you the potential differential in volts between your service ground and the docks natural water ground without the upstream neutral bond raising/lowering the reading

I am still of the opinion that the local N/G bond is giving you the current flow. I have seen this type of craziness in places where the utility is letting phases slip outa whack and the transformers generate a strange neutral that actually has voltage of it's own to ground.

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Regards,

[cking]

A little history note you don't need the neutral. Feston lighting, during early days killed alot of people because it was one hot wire and at the end they drove a stake in ground. So in effect the neutral and grounds are all for safety. The neutral is designed to return the juice to safe point instead of you becoming the safe point. Because connections get corroded over time, the neutral became hot some what and carried a potential, so more people died. Then came grounding wire green, not supposed to carry any juice and supposed to be a better ground than you could ever be even if standing in a puddle. Again it suffers from connection point resistence.

Ground loops, is caused by different potentials of multiple grounds. If you look at todays power poles you see that every one of them has copper wire down side around bottom this connects to neutral, then goes up and works as lightening arrest for hot wire usual about 4 inch standoff.

Three phase is little different animal, in that you don't need a neutral big enough to carry the total current from all three phases. because when they meet on neutral they cancel each other out.

Even on single phase 220 houses feeds they let you derate the neutral.

So on your dock, don't strap the neutral and ground together. Put a ground stake in and tie all the green third prongs to that and your shock problem will go away without a lot of digging and work. I would still put a Gfi on that circuit so some fool who uses a power and falls in water with it won't die. Nice 10 foot ground rod on edge of lack will make a wonderful ground, however if you strap neutral and grounds together you may have best ground in neighborhood and have lots of juice flowing towards it.

It just like water all seeking the lowest potential.

[EricW]

So in effect the neutral and grounds are all for safety. The neutral is designed to return the juice to safe point instead of you becoming the safe point.

Not quite. The neutral is a by-product of the Delta-Wye stepdown transformer used to go from line voltage to service voltage.

If you look at todays power poles you see that every one of them has copper wire down side around bottom this connects to neutral, then goes up and works as lightening arrest for hot wire usual about 4 inch standoff.

I have to disagree. Unless there is a transformer bank on the pole, that ground wire is for lightning protection only. Power is typically transmitted between transformers wired in Delta - for which there is no neutral. The 4th or 5th wires that you see above the a,b,c phases are to absorb lightning strikes. The neutral is created at the step-down transformer bank.

[/Not an electrician, but I paid a lot of money to pretend I'm one Mode]

[Gun Geek]

So on your dock, don't strap the neutral and ground together. Put a ground stake in and tie all the green third prongs to that and your shock problem will go away without a lot of digging and work. I would still put a Gfi on that circuit so some fool who uses a power and falls in water with it won't die. Nice 10 foot ground rod on edge of lack will make a wonderful ground, however if you strap neutral and grounds together you may have best ground in neighborhood and have lots of juice flowing towards it.

It just like water all seeking the lowest potential.

<{POST_SNAPBACK}>

Ahhhhh, nobody's listening, I'll go over this again...

The N & G are NOT tied together - they never have been.

At one time there was no G - The N was tied to the frame of the dock (this is really bad). Now the N is isolated and the G is tied to the dock. The G comes directly off of the ground rod up the hill.

You still get shocked, even if the power is shut off and the N is disconnected (leaving only the G connected). Disconnect the G and the shock goes away.

Putting in a ground stake on the shore is not an option (unless I rent one of those self propelled drills they use to make blast holes for clearing road right of way). The shore of the lake is solid limestone.

I don't have 10' of topsoil at the top of the hill for a ground rod only 3 or 4' then you hit limestone.

All plugs are GFCI, and I have tested them by dropping a hot wire into the water.

Not picking on you cking - this thread has gotten a little hard to follow, but it is very interesting, so keep it all coming!

[EricW]

GG,

You might try contacting your electrical utility under a pseudonym to see if they have any solutions/ideas for achieving a solid ground into limestone. This can't be the first time this has happened. We have lots of basalt where I live, so I'm sure that this issue has been dealt with before.

FWIW, I do understand what your problem is.

[Gun Geek]

GG,

You might try contacting your electrical utility under a pseudonym to see if they have any solutions/ideas for achieving a solid ground into limestone.  This can't be the first time this has happened.  We have lots of basalt where I live, so I'm sure that this issue has been dealt with before. 

FWIW,  I do understand what your problem is. 

<{POST_SNAPBACK}>

It is good to be understood.

I talked to the U Co this morning. Their answer was call an electrician. I think this is a standard to keep themselves from getting sued.

I'm working to find an electrician who will help with out turning me over to the fuzz. Actually I don't think you can get "turned in". What happens is that if you need help from the U Co they won't give it to you unless there is an electrican involved and things are already up to snuff. Which, I guess makes sense...

[George]

If you DIY, it obviously can't be up to code ;-) That's why your friendly neighborhood utility company won't pay any attention to you until a licensed contractor says so for you.

cking, Eric is right about only the poles with transformers having a real grounding wire to the neutral. And there are no neutrals ahead of the transformers, neutrals are all figments of induction and generated locally when needed ;-)

The whole idea of the ground and neutral being tied again in the service box after they are already tied at the pole/transformer and the dock getting it's ground wire directly from the ground rod instead of through the main service can flys in the face of any single point ground strategy.

Take it from me. The utility has a ground strap from neutral right at your transformer secondary. You should only take the ground for the dock from the buss in the service box, which then gets it's ground right from the ground stake. Any other method will allow for multiple ground paths of varying resistance and will bite you in the butt from behind ;-)

The neutral strap at the service box is NOT really needed if you have a real solid ground in the first place and your house wiring carries it everywhere on actual wire, not just with conduit. It is just a code afterthought to prevent lousy connections from causing a high neutral. A bandaid fix in effect.

Any electrician you hire will agree with me overall (although he may have to do the G/N strap according to your local code, you can remove it later if you don't find a voltage potential across G/N like I mentioned in a previous post).

In the long run the contractor you choose just might wind up recommending my first suggestion of using all plastic distribution hardware and floating the whole sumbich with the ground lug, the neutral and the hots in the GFCI outlets going right straight back to the service box on properly gauged, rated and protected cabling. You will probably also wind up with a sub-panel at the dock with local breakers to protect the long wire runs from the main service.

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Regards,

[bgary]

This is a well known and well documented problem around marinas (and one of the reasons you're not supposed to swim around them).

Especially salt-water marinas.

Most boats in salt water have sacrificial zincs, so that the galvanic corrosion that *is* going to happen will happen to something cheap, rather than, oh, say, the motor, the mast, etc.

Most places, a right-sized zinc will last 6 months to a year. I've been in some marinas where the same zinc would be gone in a week... usually traceable to some yahoo down the way who grounded everything to a copper plate and left the shore power attached.... making the whole marina "hot".

Bruce

[George]

They show it bonded to the enclosure and to an enclosure around a load - the frame of the dock.

BTW GG, the dock is not an enclosure at all and is more like a metal work bench in this instance. The grounded metal shell would be the case of a toaster, fridge, electric drill etc...., not the dock. In fact, if the dock is grounded and voltage faults to the grounded chassis of an object being held by someone standing on the metal dock with bare/wet feet, the ground path will probably become the person, not the ground wire attached to the device.

Based on this possible scenario I still recommend floating the dock (every pun intended) and just grounding the devices used through the ground lug on the outlet they are plugged into. That way fault current only has ONE path to ground and it will NOT be through a person.

Dropping a power drill in water is what the GFCI's are for, not a grounded dock.

--

Regards,

[lefty45]

GG you might look into the NEC as a reference for bonding/not bonding the dock to the grounding electrode system. In most cases, all non current carrying metal parts that might become energized are to be bonded to the grounding electrode system. Although art. 553 "floating building" might not not exactly apply, It might get you started in the right direction, look at 553.11. art 555 Marinas and boatyards doesn't apply to single family dwelling docks. art 250 would apply.

One thing to keep in mind is that the NEC is a minimum standard for practical safeguarding from the hazards of the use of electricity. as we say it is a D- just to pass an inspection.

there are several online forums for the electrical industry that might be a place to find some advice. MikeHolt.com is a good one

any conversation with the neighbors?

If I were a little closer I would be there to look at this very interesting situation.