electric leakage - marina boat dock

mgookin

Senior Member
Location
Fort Myers, FL
Did the boat lift have GFCI protection (like it should have)?

I've seen the service neutral/ground be at an elevated voltage from the waterway. When the mains were shut off, the voltage was still there, lift the incoming service neutral from the meter bus and it was gone. If that condition existed, having GFCI protection would not prevent the grounded boat lift from shocking those 2 boys. Was there an investigation to determine what the cause of the ESD was?

Edit: Since I observed that condition, I've driven 20' of ground rod near the waterway and tied it back to the service neutral for all jobs I work on. The PoCo does not consider this there problem (which I can't understand how it's not their problem).
I don't know if the lift had GFCI or how old it was. Lifts have been around for a very long time. That lift may have been new or maybe not; I don't know.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Did the boat lift have GFCI protection (like it should have)?

I've seen the service neutral/ground be at an elevated voltage from the waterway. When the mains were shut off, the voltage was still there, lift the incoming service neutral from the meter bus and it was gone. If that condition existed, having GFCI protection would not prevent the grounded boat lift from shocking those 2 boys. Was there an investigation to determine what the cause of the ESD was?

Edit: Since I observed that condition, I've driven 20' of ground rod near the waterway and tied it back to the service neutral for all jobs I work on. The PoCo does not consider this there problem (which I can't understand how it's not their problem).
That doesn't really do anything to solve the problem. That only raises the voltage of the earth for a small area around the ground rod.
 

oldsparky52

Senior Member
That doesn't really do anything to solve the problem. That only raises the voltage of the earth for a small area around the ground rod.
I understand and agree, but if the PoCo won't investigate and says you have a grounding problem ..... ????

My thinking was the water is such a good conductor (our water is salt water) that driving a GR close to the water would have the GR in the water under the sand surface and make a better electrical connection between the service neutral and the water. I have concern that I don't know if I'm aggravating the situation or not.

What would you suggest be done with a PoCo that won't act on something like this?
 

mgookin

Senior Member
Location
Fort Myers, FL
I understand and agree, but if the PoCo won't investigate and says you have a grounding problem ..... ????

My thinking was the water is such a good conductor (our water is salt water) that driving a GR close to the water would have the GR in the water under the sand surface and make a better electrical connection between the service neutral and the water. I have concern that I don't know if I'm aggravating the situation or not.

What would you suggest be done with a PoCo that won't act on something like this?
Is it possible (or probable) that the problem comes from a neighbor on the same tranny?
 

oldsparky52

Senior Member
Does anyone have a sketch of the current path that shows this diagrammatically?
We are discussing a couple of different issues, one of them being a leakage from a piece of electrical equipment, leakage from a conductor, and then the PoCo multi grounded distribution that a deteriorating neutral connection that can send current to the water as a parallel path back to the source.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
I understand and agree, but if the PoCo won't investigate and says you have a grounding problem ..... ????

My thinking was the water is such a good conductor (our water is salt water) that driving a GR close to the water would have the GR in the water under the sand surface and make a better electrical connection between the service neutral and the water. I have concern that I don't know if I'm aggravating the situation or not.

What would you suggest be done with a PoCo that won't act on something like this?
In some rural areas where this same issue causes problems for livestock, sometimes you can get a neutral blocker installed to remove the connection between the utility neutral and the electrical equipment.
 

GoldDigger

Moderator
Staff member
In some rural areas where this same issue causes problems for livestock, sometimes you can get a neutral blocker installed to remove the connection between the utility neutral and the electrical equipment.
Unless POCO has a totally degraded neutral and until they can schedule a replacement, the neutral blocker is the best solution you are likely to get.
That allows your working ground to establish a local equipotential without POCO current setting up an earth gradient.
Note carefully that if the earth to neutral voltage offset is more than 22 volts the linked product will not work.
In that case POCO will have no choice but to take real corrective action.
 

oldsparky52

Senior Member
For that neutral blocker to work, does the neutral on the discharge side not get referenced to ground (other than through the neutral blocker circuit back to the line side grounding? I hope that question makes sense.
 

GoldDigger

Moderator
Staff member
For that neutral blocker to work, does the neutral on the discharge side not get referenced to ground (other than through the neutral blocker circuit back to the line side grounding? I hope that question makes sense.
The operation of the neutral blocker, AFAIK, is that the POCO secondary neutral goes directly to the customer where it is bonded to ground but it's connection to the primary side MGN is through the neutral blocker.
The result is that fault current from lightning or a primary hot wire falling on secondary wiring goes through the neutral blocker to the MGN so that there is a metallic fault path to trip any primary side overcurrent protection. But as long as the MGN to remote earth voltage does not go above 22 volts the secondary circuit has its own ground reference at the service disconnect. And that ground electrode is not forced to carry primary voltage operating current (which would otherwise take that path because of a degraded primary neutral or other problem.)
 

oldsparky52

Senior Member
The operation of the neutral blocker, AFAIK, is that the POCO secondary neutral goes directly to the customer where it is bonded to ground but it's connection to the primary side MGN is through the neutral blocker.
The result is that fault current from lightning or a primary hot wire falling on secondary wiring goes through the neutral blocker to the MGN so that there is a metallic fault path to trip any primary side overcurrent protection. But as long as the MGN to remote earth voltage does not go above 22 volts the secondary circuit has its own ground reference at the service disconnect. And that ground electrode is not forced to carry primary voltage operating current (which would otherwise take that path because of a degraded primary neutral or other problem.)
Thank you for that explanation. Very nice.
 

luckylerado

Senior Member
The answer is proper grounding and bonding, providing GFCI protection, using a durable wiring method and making sure there is a proper neutral to ground connection at the service. If all of that is done every time then the chances of something like this happening would be nill.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
The answer is proper grounding and bonding, providing GFCI protection, using a durable wiring method and making sure there is a proper neutral to ground connection at the service. If all of that is done every time then the chances of something like this happening would be nill.
While that takes care of a large percentage of the issues, none of that does anything for problems caused by an elevated neutral to earth voltage.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I would like to read an article that reported drowning from swimming in a salt water marina, if someone has a link, please share.
This is a Mike Holt article that I republished for my contractors association. In no cases were salt water electrical shocks cited :

http://www.pceca.net/images/stories/mike holt electric shock drownings.pdf

This is an article from the March 2014 edition of EC Magazine by Mike Lamendola regarding wiring for marinas and boat yards :

http://www.pceca.net/images/stories/wiring requirements for marinas and boatyards.pdf

Hope this is helpful.
 

oldsparky52

Senior Member
This is a Mike Holt article that I republished for my contractors association. In no cases were salt water electrical shocks cited :
I think that's what Fitzdrew516 and I were trying to point out. This problem does not seem to be reported in salt water conditions. The ESD problem that is, if you have a boat lift with a ground fault, that is a different story.

Most ESD's as I understand it work off the same principle as step voltage shock (like that video someone posted a while back about a guy getting out of his car with energized wires on the ground). Since salt water has a much lower resistance, a swimmer will not have as much current passing through it's body as they would under the same voltage conditions in fresh water.

This is not to say that I think we should not be heading towards where the code is taking this. Safety around water is paramount. My concern is they (code) are not doing anything about detecting elevated neutral/ground to water voltages that are not coming from the dock wiring. Most people don't seem to even understand that this can be a concern.
 

Fitzdrew516

Senior Member
Location
Cincinnati, OH
I think that's what Fitzdrew516 and I were trying to point out. This problem does not seem to be reported in salt water conditions. The ESD problem that is, if you have a boat lift with a ground fault, that is a different story.

Most ESD's as I understand it work off the same principle as step voltage shock (like that video someone posted a while back about a guy getting out of his car with energized wires on the ground). Since salt water has a much lower resistance, a swimmer will not have as much current passing through it's body as they would under the same voltage conditions in fresh water.

This is not to say that I think we should not be heading towards where the code is taking this. Safety around water is paramount. My concern is they (code) are not doing anything about detecting elevated neutral/ground to water voltages that are not coming from the dock wiring. Most people don't seem to even understand that this can be a concern.
Yes. Exactly. The only possible way I could think of ESD occurring in anything other than freshwater is if it were to occur in brackish water - Especially brackish water with a low salinity. But in true "salt water" I can't see this happening due to the high conductivity of the water itself. In saltwater applications the current running through the water, when it reaches a would be victim, the vast majority of the current would travel through the water instead of the human (water is the less resistive load).
So again thinking of this - I think maybe if it was a small child in brackish water (depending on the salinity) it may pose a risk due to the child having a lot less resistance than the normal human. Can anyone else think of instances where saltwater could harbor the effects of ESD?
 

kwired

Electron manager
Location
NE Nebraska
The best advice is that no one is in the water within a 100' from the dock. One of the issues is an elevated neutral to ground voltage that also acts to elevate the voltage of the EGC and can cause problems.
Best answer IMO. You have no control over what voltage to ground may be on the utility side of your service, and because it is bonded to the customer side grounded conductor it is on all equipment grounding conductors.

No one needs to be swimming in the area around the docks for other safety reasons anyway, especially public dock areas.

As far as salt water - the fact it is more conductive means voltage gradients that do exist are in larger zones and it is harder to physically reach across enough zone to be exposed to enough potential to be a problem.
 
The higher conductivity of saltwater may protect against electric-shock drownings (ESD) in the water, but increases the hazard of incidental contact such as grasping an energized handrail or wire rope dangling from a winch.
 
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