Ok troubleshooting wizards

[hardworkingstiff]

Got a call about someone getting shocked when they put their hand in the water at a homeowners association's docks. It's one that I helped remodel back in February. Marina Power and light power centers with a light and GFI receptacle only (no shore power for boats, they are small boats). Panel is about 150? from the ramp to the floating docks. Ramp is aluminum. I ran 4 #6?s (cu.) in PVC and non-metallic flex from the existing panel to the dock and loop fed the power centers with ? of the pedestals on one circuit and the other ? on the other (used 30-amp breakers). I also bonded the aluminum ramp to the ground wire I ran for the power centers.

Here is what I found. With one test lead in the water and one on the ramp, I found 1.9 volts AC. Switched to DC and found less than .01-volts (discounted it as meter sensitivity). I turned off the 200-amp MB in the panel and found the 1.9-volts still present.

I quickly dipped my hand in the water while holding the ramp and felt a little tingle. It was weird though, like only on one finger in one certain area of the finger. I bent that one over and dipped the other three fingers and no sense of shock. I put the ?shocking? finger back in and again the tingle (fairly strong). It turns out that I have about a ?? diameter abrasion from work this week and the 1.9-volts caused the tingling there, but not on my normal skin.

Love to hear comments please.

Thanks,
Lou

 

[77401]

Main breaker off & still the tingle?

OK leave the MB off & then disconnect the ground/bond/neutral at the fartherst point the the feed is originating from.

In other words disconnect everything you did!

It might be coming from another Marina & all thats left is 1.9V by the time it gets to you?

 

[hardworkingstiff]

Main breaker off & still the tingle?

It might be coming from another Marina & all thats left is 1.9V by the time it gets to you?

Nothing very close.

I'm wondering if the ICW (Intra Coastal Waterway) is a better path (or at least a path) back to the substation than the wiring.

 

[77401]

A broken neutral upstream from your install could be using your ground(s) for a path. Thats why I suggest disconnecting all of your new install and rechecking it.
Also from a liability aspect it will protect you in case someone get hurts later from a higher voltage.

 

[e57]

I would doubt the other marina idea....

The panel sounds a bit far away, in light of 555.7, but thats subjective. But this distance could lead to another problem.

I think you might have a difference in (Earth) ground potential. Is there any electrodes at the ramp, say in close proximity to the water. I don't do any marina work (Except for house boats years ago) but would think it could be looked at as a seperate strucure, and need an electrode, and other bonding as if it were.

Add: Your ground at the ramp is an extention of the ground system that goes back to the electrodes at the main, (connected at neutral bond) and also connected to the transformer for the area, making it a touch or step potential hazard. If there isn't an electrode there, adding one may eliminate it.

 

[gobblerhuntr]

I have had a similar setup but at a pool at a house. Tingle coming from the water to the ladder. Measured less than 10v ac. We pulled the POCO meter outta the house and the problem was still there. Eventually we found a bad neutral connection on the distribution lines down the street. The return was going to any place it could find. I work for the POCO so we could pull the meter test it that way. We did cut the neutral loose from the weatherhead and all grounds and that stopped it. I would think that your problem could be coming from a neighbor with a problem and not you. I would isolate all incoming power, including neutals and ground (including telephone and cable tv) and see if the problem was still there and see if you are generating the problem.

 

[hillbilly]

I would doubt the other marina idea....

The panel sounds a bit far away, in light of 555.7, but thats subjective. But this distance could lead to another problem.

I think you might have a difference in (Earth) ground potential. Is there any electrodes at the ramp, say in close proximity to the water. I don't do any marina work (Except for house boats years ago) but would think it could be looked at as a seperate strucure, and need an electrode, and other bonding as if it were.

Add: Your ground at the ramp is an extention of the ground system that goes back to the electrodes at the main, (connected at neutral bond) and also connected to the transformer for the area, making it a touch or step potential hazard. If there isn't an electrode there, adding one may eliminate it.

A agree with e57. IMO you should treat your installation as a seperate structure and install a grounding electrode and bond as required.
steve

 

[77401]

Eventually we found a bad neutral connection on the distribution lines down the street. The return was going to any place it could find.

I understand this! It makes sense.
Was the bad neutral on the line side of a transformer?
Any more details would be very interesting.

 

[George Stolz]

This PDF (courtesy of Mike Holt's newsletter) structures how to test for stray voltage.

It's written with farms in mind, but might be helpful as you track down the stray voltage passing through your area.

Good luck!

 

[gobblerhuntr]

I understand this! It makes sense.
Was the bad neutral on the line side of a transformer?
Any more details would be very interesting.

The bad connection was about 3 or 4 spans away back toward the source (substation). It was almost burnt completely into the guy said that replaced it. I was on a single phase tap that had a minimum load on it, and also was about 4 miles from the substation.

 

[ramsy]

Main breaker off & still the tingle? OK leave the MB off & then disconnect the ground/bond/neutral.. It might be coming from (somewhere else)

Since all the good idea's are already taken, you guys leave me with nearby vessels leaking AC from their hulls.

Boats with conductive parts in the water leaking their generator or DC-to-AC inverter power into the water, close to the aluminum dock that "hardstiff" bonded with his EGC.

I'd monitor the 1.9vac with a logging meter, tell the marina to log each vessel's dock & departure, or manual power down if moored, then try to match the meter's 1.9vac record with an offending vessel.

If that 1.9vac dissapears when that dock bond is liftted, then you know some other source is using your bonding path, and if your lights don't dim, after lifting that bond from the aluminum dock, then your neutral is not likely damaged.

 

[hardworkingstiff]

Met with the PoCo service man today. There was 1.5 volts between the ramp and the water today. I asked him to lift the neutral to the meterbase and when he did the voltage went away between the ramp and ICW. The service man said they would check their cable for leakage and if it tested OK, the problem will be the customer's.

 

[LarryFine]

Met with the PoCo service man today. There was 1.5 volts between the ramp and the water today. I asked him to lift the neutral to the meterbase and when he did the voltage went away between the ramp and ICW. The service man said they would check their cable for leakage and if it tested OK, the problem will be the customer's.

Couldn't you have tested between a temporary local ground (even a large screwdriver) and both sides of the lifted neutral as an additional test?

 

[hardworkingstiff]

Couldn't you have tested between a temporary local ground (even a large screwdriver) and both sides of the lifted neutral as an additional test?

Sure, but I'm curious, what would the test results tell you?

 

[gobblerhuntr]

Right after posting I got a call at work with another one of these pool stray voltage problems. Went over there and determined that it was not coming from the homeowner and lifted the service neutral from our system neutral on the pole and the voltage went away. So backed up and killed the primary distrubution line feeding the street and the voltage was still on it. Killed another section of line that fed on to the back of the subdivision and the voltage was still there. My next step it to kill the whole subdivision and see if the voltage is being generated from somewhere in the subdivision. If that doesn't do it we are going to purchase a Ronk "blocker" on the service. I have a adjoining POCO that has used these on dairy barns and swimming pools with the same problem and it has taken the voltage away. If anyone is interested in these blockers, do a google on Ronk and look under products and it is described there. Hope this helps.....

 

[George Stolz]

If anyone is interested in these blockers, do a google on Ronk and look under products and it is described there. Hope this helps.....

I did, and here's the link for those who're lazier than I am:
http://www.ronkelectrical.com/pages/otherproducts.html

I'm very curious how it works, though?

 

[LarryFine]

Sure, but I'm curious, what would the test results tell you?

I would think that the opened neutral on the side of the source of the stray voltage would produce a voltage reading to earth, while the other neutral would have no voltage-to-earth reading. This would, of course, require a high-impedance meter, and not a solenoid tester.

 

[e57]

Can some explain what "Stray Voltage" is... I really dont think this voltage is wandering around on its own.

In the OP scenario he has a difference in potential between is EGC that is run from a considerable distance away. Which is grounded to earth in close proximity to the panel there on 'terra firma', dry land. I imagine that this same voltage reading is not being measured there?

 

[George Stolz]

Can some explain what "Stray Voltage" is... I really dont think this voltage is wandering around on its own.

Here is one of Mike Holt's newsletters that goes into detail. More can be found here.

Edit to add:

A very simplified way to look at this is to examine a circuit with a current source (neutral return current) and two current paths (neutral path and earth path). All else being equal, current will follow all return paths in proportion to the conducting path impedances. Therefore, reducing the impedance of the neutral effectively reduces the amount of current flowing through the earth path and lowers corresponding NEV (neutral to remote earth voltage) at that neutral-to-ground bonding point.

 

[e57]

Thanks for that George.

One article in particular about the varying and vague definitions of stray voltage caught my eye.

http://www.mikeholt.com/newsletters.php?action=display&letterID=176

Another which describes simular situations to this one as "Neutral to Earth Voltage" ~ http://www.mikeholt.com/newsletters.php?action=display&letterID=68

This voltage potential can be metallically transmitted over to a remote earth point through code-required grounding and bonding of water pipes, neutrals and other metallic objects. It is important to note that NEV is a normal occurrence caused by the intentional grounding of the power system.

Still think dropping a rod near the ramp will minimize or eliminate the problem. And code requires it as it is a seperate structure with more than one circuit.

Edit: (Actually a few of those articles start with the vaguaries of the definition of the term.)