I am reading 2.8 volts A/C between the aluminum I-beam which is attached to my boat lift motor and the water below. I read the same even with the service main in the off possition. (No power beyond my service main breaker.) I feel certain that the voltage that I am seeing is coming in on the utility neutral but I have not had the utility neutral disconnected from the service to check it. I allowed the utility engineer to steer me in another direction when I should have insisted on disconnecting the neutral from my service but anyway.. His reponse was What will that prove? I plan on inviteing the utility guys back and verifying this but with that being said, assuming the voltage is actually coming in on the utility neutral, I was thinking that if I could convence the utility company to drive additional ground rods at the base of the utility pole the voltage should decrease as the resitance decreases.. Any thoughts or suggestions?
Neutral to Ground Voltage @ Boat Lift
- Thread starter rutsd
- Start date
- Status
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
110527-1300 EDT
Do some more experiments. Use a 10 megohm input impedance meter that has a millivolt capability. I have both a Fluke, 27 and 87, and a Beckman 4410. I use 10 or 12 inch long screwdrivers for probes.
Hopefully the power company transformer is not a 1000 ft away. Its distance will determine how long a wire you need to extend your meter test lead. Find the transformer ground rod and connect it to one meter input. This becomes your reference point.
(1) Measure the voltage to the main panel ground rod or whatever the electrode is.
(2) To the main panel neutral.
(3) To the water.
(4) To the boat lift frame.
How is the boat lift frame grounded?
(5) Pick some various points in the earth for voltage measurements.
(6) With 20 to 50 ft of wire make some measurements between a point in the water near the lift and some surrounding earth points.
Report back.
.
Do some more experiments. Use a 10 megohm input impedance meter that has a millivolt capability. I have both a Fluke, 27 and 87, and a Beckman 4410. I use 10 or 12 inch long screwdrivers for probes.
Hopefully the power company transformer is not a 1000 ft away. Its distance will determine how long a wire you need to extend your meter test lead. Find the transformer ground rod and connect it to one meter input. This becomes your reference point.
(1) Measure the voltage to the main panel ground rod or whatever the electrode is.
(2) To the main panel neutral.
(3) To the water.
(4) To the boat lift frame.
How is the boat lift frame grounded?
(5) Pick some various points in the earth for voltage measurements.
(6) With 20 to 50 ft of wire make some measurements between a point in the water near the lift and some surrounding earth points.
Report back.
.
- Location
- Illinois
- Occupation
- retired electrician
Driving additional ground rods will not change this voltage. This voltage is the voltage drop on the primary and secondary grounded conductors. The only thing that will get rid of it is some type of neutral isolation device.
Boat Lift
Boat Lift
When the utility guys came to visit they were very interested for the first hour but after inspecting all of my connections they did some test using the utility ground rod, a piece of THHN wire & a seperate ground rod. The voltage near the pole between the two rods was approximately .2-volt less than what we are reading 450-feet away between the boat lift to water.
There are two homes fed from this utility transformer & both appear to see about the same voltage readings between lift & water. The utility guys say to go ahead & bond the motor with a piece of bare copper wire & drop that into the salt water. (Put voltage into the water so it isnt detected.) Not sure if there is a better way.
Boat Lift
When the utility guys came to visit they were very interested for the first hour but after inspecting all of my connections they did some test using the utility ground rod, a piece of THHN wire & a seperate ground rod. The voltage near the pole between the two rods was approximately .2-volt less than what we are reading 450-feet away between the boat lift to water.
There are two homes fed from this utility transformer & both appear to see about the same voltage readings between lift & water. The utility guys say to go ahead & bond the motor with a piece of bare copper wire & drop that into the salt water. (Put voltage into the water so it isnt detected.) Not sure if there is a better way.
- Location
- Illinois
- Occupation
- retired electrician
That will only make a difference for a small area around the wire that is in the water.
The reason I thought the additional ground rods @ the base of the pole mounted utility transformer would be the ticket is because the first time I measured the voltage between I-beam & water, the soil conditions around the utility ground rod were extremly dry however the next time I checked the voltage the soil was saturated and the voltage had dropped about 1 volt. To me the damp soil would lower the resistance at the utility ground rod. (E=IxR) If the actual resistance @ the ground rods was 0 wouldn't the voltage be the same?
- Location
- Illinois
- Occupation
- retired electrician
There could be a lot of reasons why you measured a lower voltage and one of those could be the soil conditions, but more likely it was the utility load. This voltage is most likely the voltage drop on the utility primary grounded conductor and a lower load would mean a lower voltage drop. Some of it could also be the voltage drop on the service grounded conductor.
The ground rods are only placing the earth in parallel with the grounded conductor and additional rods won't lower the resistance of the parallel path to make much of a difference. The utility grounded conductor is connected to earth every 1/4 mile and at every transformer. A rain storm in the general area could make a difference as it would lower the resistance at all of these grounding electrodes.
Thanks for all your help with this unusual voltage problem. Seems as if the neutral isolation device is a possible solution to the 2-volts that we are seeing between the water and the aluminum lift beam. I dont have experience with this type of equipment and would have to assume that this would be something that would be installed by the utility company. Can anyone explain how I would go about installing or having one installed?
Where I work we have a RV park. We had a situation where a child was recieving an electrical shock when he touched one of the RV pedistals. The electricians discoverd that the problem was common throughout the park at all the pedistals. After hours of head scratching they found that the 3-volts that they were reading was coming from one of the CATV utility companys amplifiers at the parks entrance. The cable company removed & replaced the device with a new one in a new location and the problem went away. I thought this was interesting and might be helpful.
Where I work we have a RV park. We had a situation where a child was recieving an electrical shock when he touched one of the RV pedistals. The electricians discoverd that the problem was common throughout the park at all the pedistals. After hours of head scratching they found that the 3-volts that they were reading was coming from one of the CATV utility companys amplifiers at the parks entrance. The cable company removed & replaced the device with a new one in a new location and the problem went away. I thought this was interesting and might be helpful.
- Location
- Illinois
- Occupation
- retired electrician
Utilities are often very reluctant to install a neutral isolator.
Thats kinda what I thought. The utility company frowns on these devices attached to there transformers. It would seem to me that when there is any amount of voltage that originates from the power company in the area near the water that they would want to remove it from the system if possible. I guess they already realize that this is a common problem around boat houses and feel that there isn't enough voltage to endanger the residents. The only problem is that I have a 8-year old niece that plays around the dock & the very thought of voltage in and around the water disturbs me! What do other electricians and contractors do when they encounter this problem? From what I have read from other instances like this, the utility company makes a showing, inspects the customers electrical system and when the voltage originates from utilty companys system and they test there transformer to make sure its ok, there out of there. Oh yea, as there driving off they might say, "Its just a differance in potential." What there saying is there's voltage on our neutral and you can fix this problem by installing a piece of wire between the grounded frame of your motor and the water. Now you are at the same potential with the same voltage in the water and at the lift, only now you wont feel it! Sounds like it starting to eat at me doesn't it?
- Location
- Illinois
- Occupation
- retired electrician
Bonding the water will not solve this problem. It will only raise the voltage of the water for a very small area around the bonding conductor.
With a creative application of 250.110 and a 240 to 120/240 volt transformer, you can create a system that does not have a direct connection to the utility grounded conductor.
kwired
Electron manager
- Location
- NE Nebraska
I would disconnect the boat hoist and EGC until the issue is resolved. Not worth getting someone killed. I would also bring the matter to the attention of POCO, if they don't want to do anything about it, contact someone higher up the chain of command. If you still can't get anything done go to public health and safety officials. Before doing any of this I may see if any neighbors have similar problems - they likely do.
Around here if there is that kind of voltage potential between objects like that around a dairy farm POCO is there right away trying to find out if it is their problem of customers problem. Dairy cows are very sensitive to pretty low currents and causes health and production problems. If POCO eventually is found to be the source of problem they are subject to lawsuits.
If all connections are good and problem is just voltage drop on primary neutral they can reduce neutral current by better balancing load. Better than getting someone killed just because they did not want to do anything about it.
- Location
- Illinois
- Occupation
- retired electrician
But the issue is that at primary distribution voltages the drop is very very small in percent. A 10 volt drop on the grounded conductor of a 13.8 kV distribution system is a 0.000007% drop. The real answer is for the utility not to use line to neutral transformers. If the distribution transformers are all connected line to line, there is no voltage drop on the primary grounded conductor.
mivey
Senior Member
Balancing the single-phase loads also helps. Not an option with a long single-phase line but it will help up to the point of the single-phase take-offs.
kwired
Electron manager
- Location
- NE Nebraska
Does not matter, they are still introducing hazardous voltage to the general public - might as well run their distribution system on 6 foot tall poles and not guard them with anything will be about the same level of safety as is it is for anyone swimming near the boat hoist.
Not using the primary grounded neutral would work, but then they would be tempted to just use a grounded phase system and still have the same problem.
mivey
Senior Member
There are not always simple choices.
Not even in the same solar system as far as hazards go.
The POCOs would be willing to make things as safe as the users and regulating authorities would be willing to let the rates allow. The problem is that the end users eventually protest at the cost so a decision is made about how much safety can you afford. The economics drive the boat. Think about how many POCOs are customer owned and operated and guess what: they run they same way as the others.
There are varying degrees of safety and concerns at one level vs. another. There are many debates on farm and water safety and MH has had several newsletters and discussions that cover the topic nicely. From what I have observed, Mike has learned a lot over the years.
kwired
Electron manager
- Location
- NE Nebraska
Try telling that to the family of someone that has been electrocuted. Their relative is just as dead either way.
kwired
Electron manager
- Location
- NE Nebraska
All POCO around here are publicly owned. And I believe all of them would be investigating the cause of the OP's problem immediately, if anything to ensure that their equipment is not the source of trouble so that from a liability point of view they are not responsible for what could happen. If they find that the problem is on customer premisis wiring they will inform them of that, even if it is not the customer that called with the original complaint.
POCO is required to deliver safe power. They are just doing their job to ensure that it is safe when something like this happens.
I am willing to guess that the non publicly owned POCO's are the ones that are more likely put off any investigation because of what it may cost in preference of profits.
- Location
- Illinois
- Occupation
- retired electrician
In general the small neutral to earth voltage is not a hazard. It can become one where there is water involved such as this case and with pools. The small amount of voltage drop that would create 5 to 10 volts of voltage drop on a system operating at 13.8 kV or higher is almost impossible to get rid of without taking extraordinary steps such as a neutral isolator. It is also some what difficult to eliminate on the load side of the service and still have a safe system that is in compliance with the NEC.
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