Dock on the lake with ground current

[winnie]

There are two possible sources of the current flowing in the lake: neutral current from the high voltage distribution system supplying power to the distribution transformers, or a fault to earth on the low voltage (120/240V) usage side of the power distribution system.

We are quick to jump to the conclusion that the problem is the high voltage neutral, because as normally designed these systems always inject a little bit of current into the soil.

However faults from the low voltage side of things to soil can also inject current into the ground and water. This current will be finding its way back to the neutral of the distribution transformer via all of the various grounding electrodes.

A specific risk for this is well pump wiring. An underground well casing is an excellent grounding electrode. If the well casing is not properly bonded back to the service, and the well wiring faults to the case, then the well can inject quite a bit of current into the soil.

Another known risk are pumps in lakes used as water sources. If there isn't proper bonding, and there is a fault, then the pump can inject current into the surrounding water. There was a thread recently about drowning risks from these pumps.

-Jonathan

 

[kwired]

There are two possible sources of the current flowing in the lake: neutral current from the high voltage distribution system supplying power to the distribution transformers, or a fault to earth on the low voltage (120/240V) usage side of the power distribution system.

We are quick to jump to the conclusion that the problem is the high voltage neutral, because as normally designed these systems always inject a little bit of current into the soil.

However faults from the low voltage side of things to soil can also inject current into the ground and water. This current will be finding its way back to the neutral of the distribution transformer via all of the various grounding electrodes.

A specific risk for this is well pump wiring. An underground well casing is an excellent grounding electrode. If the well casing is not properly bonded back to the service, and the well wiring faults to the case, then the well can inject quite a bit of current into the soil.

Another known risk are pumps in lakes used as water sources. If there isn't proper bonding, and there is a fault, then the pump can inject current into the surrounding water. There was a thread recently about drowning risks from these pumps.

-Jonathan

Other than if you are swimming in vicinity near such pumps are they really any more risk than a submersible in a well casing on the shore? Or even jet pump type shallow well on the shore with metallic piping as the well?

Any of those things will have a voltage gradient in the vicinity of said "thing" and further away you get the more things become same as true earth potential. Most these that gradient drops off in pretty short distance, which is the thing that makes a hazard when near them as you can touch different potential zones at the same time.

 

[ptonsparky]

I wonder how many are hung on plastic with no EG.
Found more than one ’leaking’ back in my stray voltage & dairy barn days.

 

[tortuga]

I spoke with the POCO who confirmed he has personally checked all the wires from our point (end of the line) back to the substation. He confirmed this issue tends to be worse when it’s dry (lower earth conductivity, already poor due to rocky soil) and we’ve been in a 2-3 week hot and dry spell. It doesn’t help that in the 3 communities served by this long single line homes are continually being expanded or rebuilt so electrical load is going up.

Can you post a pic of one of the distribution transformers? Do we know is this overhead or underground? Is the primary is wired Line to neutral?

 

[winnie]

Other than if you are swimming in vicinity near such pumps are they really any more risk than a submersible in a well casing on the shore? Or even jet pump type shallow well on the shore with metallic piping as the well?

Any of those things will have a voltage gradient in the vicinity of said "thing" and further away you get the more things become same as true earth potential. Most these that gradient drops off in pretty short distance, which is the thing that makes a hazard when near them as you can touch different potential zones at the same time.

I don't know the relative risks, and am not sure there is good data available.

You might poke around the Army Corps of Engineers to see if they have data; they do have a policy prohibiting submersible pumps in lakes:

https://www.swf-wc.usace.army.mil/Belton/images/ElectricSubmersiblePumpInformation.pdf

 

[tortuga]

Here is a interesting youtube video where a guy experiments with a few voltages thru ground, note only the 120 volt would apply to residential as residential here is split phase with only 120 to ground. I think he uses a 75VA control transformer in reverse appears to use a distance of 200'.

 

[kwired]

I don't know the relative risks, and am not sure there is good data available.

You might poke around the Army Corps of Engineers to see if they have data; they do have a policy prohibiting submersible pumps in lakes:

https://www.swf-wc.usace.army.mil/Belton/images/ElectricSubmersiblePumpInformation.pdf

Often the "water table" below land is basically same water as what it in the nearby lake or stream, especially in my neck of the woods. This mostly goes for shallow wells that are capable of being pumped from with a jet pump.

There are deeper wells that get into better quality water.

I still don't really see that there should be that much difference in effects to someone swimming in the lake. These things have a voltage gradient in the water or earth that is nearby exposed metallic objects that are at other than earth potential, but it always drops off pretty rapidly. If you are at least 10 feet away from items operating at just 2 to 10 volts to earth you shouldn't be exposed to anything that should be harmful or likely won't even be able to feel anything.

 

[GoldDigger]

There are two possible sources of the current flowing in the lake: neutral current from the high voltage distribution system supplying power to the distribution transformers, or a fault to earth on the low voltage (120/240V) usage side of the power distribution system.

We are quick to jump to the conclusion that the problem is the high voltage neutral, because as normally designed these systems always inject a little bit of current into the soil.

However faults from the low voltage side of things to soil can also inject current into the ground and water. This current will be finding its way back to the neutral of the distribution transformer via all of the various grounding electrodes.

A specific risk for this is well pump wiring. An underground well casing is an excellent grounding electrode. If the well casing is not properly bonded back to the service, and the well wiring faults to the case, then the well can inject quite a bit of current into the soil.

Another known risk are pumps in lakes used as water sources. If there isn't proper bonding, and there is a fault, then the pump can inject current into the surrounding water. There was a thread recently about drowning risks from these pumps.

-Jonathan

A fault to casing in a well with a submersible pump can also potentially draw enough extra current to substantially raise your electric bill without tripping any OCPD for the pump. Some sort of ground fault protection (not as sensitive as GFCI, since some stray current capacitive current from long conductors immersed in water could easily trip those) would be a good idea for several reasons.
The higher the standing water level above the pump, the worse the potential problem will be.

 

[gaspower]

This is a mountain lake. The soil is rocky, the lake shoreline is steep (30-40' water depth in the boat slip of my dock) and the wells are deep. There is only one well within 0.5mi of my dock and it serves a 10k gallon storage tank so it runs intermittently. It would only be able to inject current into the ground when the pump is running and I have not observed any intermittent behavior.

never say never but the POCO also believes it is the high voltage neutral causing the issue.

Can you post a pic of one of the distribution transformers? Do we know is this overhead or underground? Is the primary is wired Line to neutral?

The communities are underground with pad mount transformers 14.4kV to 240VAC and the service to the community from the 25mi away substation is overhead. I'll take pics Wednesday when I am back up there.

 

[mm2]

So I am still confused with the application of the code for docks. Our county is still on the 2017 code but is expected to move to the 2020 code sometime this summer. Regardless I was asked to check out a dock that was put in about a year ago. There is no RCD in the main panel that feeds the sub panel on the dock. There are no RCDs in the dock sub panel. Outlets on the dock are all Class A GFCI protected at the outlets. But there is zero RCD protection for any of the equipment that is not at a convenience outlet - the boat lift motors, the water pump, etc. 18 year old high school quarterback just electrocuted somewhere else on the lake but don't have details. Seems to me even the 2017 code does not permit anything on the dock to operate without RCD protection yet the county is signing off. Seems that even residential single family dock under 2017 code requires 100mA RCD in the main panel for the sub panel on the dock. And then I think the code permits outlet level RCD (vice branch RCD) provided ALL the dock is protected. And I think I see a code difference between a shore power terminal for a boat (requires 30mA RCD) and a convenience outlet (requires 6mA RCD). Few of our residential docks have or need shore power terminals. But damn if I can figure out if the 6mA RCD can be satisfied at just the convenience outlets or if it has to be at the branch circuit level in the dock sub panel. Clearly the county has NO requirement for any RCDs for boat lifts for example.

 

[GoldDigger]

It basically comes down to whether the code refers to "outlets", which would definitely cover even hard wired boat lifts, or "receptacles", which wouldn't.
Historically, I suspect more investigated electrocutions result from boat lift faults than from any other single load type.

 

[kwired]

So I am still confused with the application of the code for docks. Our county is still on the 2017 code but is expected to move to the 2020 code sometime this summer. Regardless I was asked to check out a dock that was put in about a year ago. There is no RCD in the main panel that feeds the sub panel on the dock. There are no RCDs in the dock sub panel. Outlets on the dock are all Class A GFCI protected at the outlets. But there is zero RCD protection for any of the equipment that is not at a convenience outlet - the boat lift motors, the water pump, etc. 18 year old high school quarterback just electrocuted somewhere else on the lake but don't have details. Seems to me even the 2017 code does not permit anything on the dock to operate without RCD protection yet the county is signing off. Seems that even residential single family dock under 2017 code requires 100mA RCD in the main panel for the sub panel on the dock. And then I think the code permits outlet level RCD (vice branch RCD) provided ALL the dock is protected. And I think I see a code difference between a shore power terminal for a boat (requires 30mA RCD) and a convenience outlet (requires 6mA RCD). Few of our residential docks have or need shore power terminals. But damn if I can figure out if the 6mA RCD can be satisfied at just the convenience outlets or if it has to be at the branch circuit level in the dock sub panel. Clearly the county has NO requirement for any RCDs for boat lifts for example.

Thing is many these electrocutions and shock incidents on docks are mostly because of neutral to earth voltage (NEV) on the grounded service conductor, which inherently puts that same voltage on equipment grounding conductors beyond the service equipment. GFCI, GFPE, RCD's do not detect or respond to this voltage, they only detect situations where current is not following intended paths. It is not a problem in article 680 applications as we have equipotential bonding rules for most anything covered in art 680. Hard to have any kind of effective equipotential bonding on natural bodies of water or even large man made bodies of water.

Equipment with ground faults on docks and similar situations are not as much of an issue for shock/electrocution as those will be interrupted if GFCI, GFPE or RCD's are used and current exceeds their trip threshold.

 

[mtnelect]

Thing is many these electrocutions and shock incidents on docks are mostly because of neutral to earth voltage (NEV) on the grounded service conductor, which inherently puts that same voltage on equipment grounding conductors beyond the service equipment. GFCI, GFPE, RCD's do not detect or respond to this voltage, they only detect situations where current is not following intended paths. It is not a problem in article 680 applications as we have equipotential bonding rules for most anything covered in art 680. Hard to have any kind of effective equipotential bonding on natural bodies of water or even large man made bodies of water.

Equipment with ground faults on docks and similar situations are not as much of an issue for shock/electrocution as those will be interrupted if GFCI, GFPE or RCD's are used and current exceeds their trip threshold.

It is my position that homeowners (especially with swimming pools) shouldn't have to pay for "equipotential bonding" since the utilities MGN are responsible for "Strey Current" in the first place. The utilities should be paying homeowners for using their neutral/ground system.

 

[tortuga]

A 12.5kv source can push more electrons thru dirt than a 240V source so if its a utility issue the likely culprit is the primary side neutral not the grounded neutral on the secondary side.
We should call it what it is 'electrical trespassing'.
The fix is to use L-L distribution, a transformer with two bushings on the primary side.

 

[electrofelon]

Wish they made some sort of dye that you could use to dye the electrons to figure out where they are coming from. A mechanic did that to the oil in my car to find a leak.

 

[winnie]

You could have something like an RC boat with current and voltage probes, mapping the electric and current fields.

 

[kwired]

A 12.5kv source can push more electrons thru dirt than a 240V source so if its a utility issue the likely culprit is the primary side neutral not the grounded neutral on the secondary side.
We should call it what it is 'electrical trespassing'.
The fix is to use L-L distribution, a transformer with two bushings on the primary side.

True, but at same time 12.5 kV isn't the issue it is the voltage drop on the MGN of only a few volts. Not using the grounded conductor as a current carrying conductor would help quite a bit though.

 

[winnie]

True, but at same time 12.5 kV isn't the issue it is the voltage drop on the MGN of only a few volts. Not using the grounded conductor as a current carrying conductor would help quite a bit though.

If there is a break somewhere in the intended neutral path, you might have a system where the full primary current is getting injected into the soil. Unintentional SWER.

 

[hornetd]

That’s fair, it’s a dock for our house, no one uses it but our family. No one else but me is empowered or physically capable of plugging it in (kids can’t reach)

Have you considered replacing the conductive ladder with a non conductive one and placing an insulating mat on the Aluminum dock deck? The ladder itself may be the conductor that is allowing the utility's excess neutral current to get into the water.

You can identify the source of the stray current by opening your Service Disconnecting means and testing for current on your Service Grounded (neutral) conductor. You will need a current transformer that is compatible with your multimeter.

These can cost as much or more than the multimeter so it is often more cost effective to buy a multimeter with the current clamp built in.

If there is current flowing on the neutral with your service disconnect open it can only be coming from something off of your property. A call to your State's public utility regulating agency is one tool for addressing this. I had a couple of clients in upstate New York that had stray neutral current problems. As soon as I showed the regulatory engineer that current could be detected on the Service Entry Conductor neutral with the service disconnect open he ordered the utility to make the needed repairs or to take "Other effective measures" to prevent the neutral current from flowing onto the clients property. They had trouble crews out the same day. Every time a utility wants a rate increase the utility regulating agency's board or similar body has to vote to allow or prohibit the increase. Utility management does not dare provoke them. The regulators are very responsive to calls from state delegates or senators.

What devices like the Ronk and its cousins do is to create a high impedance to the portion of the neutral current that is not balanced with the current on the energized conductors. As long as the current flow is balanced the magnetic fields of all of the currents flowing in the service entry conductors cancel each other out so that no magnetic field is available to cause the material in the isolator to develop an opposing magnetic field in the isolator. The strength of the opposing magnetic field that is generated in the isolator is directly proportional to the amount of imbalanced current flowing on the neutral service entry conductor. The only issue is who pays for the isolator.

In some portions of the Midwest you will encounter utility transformers that are painted like the hide of a Guernsey cow. Those transformers are wired as Isolation transformers so that the neutral of the premises wiring is not connected to the utility's distribution system's multi grounded neutral. That is an absolute preventative to utility neutral current going to ground through a property's Grounding Electrode System but it is expensive. So neutral current chokes like the Ronk were developed to replace them.

Tom Horne